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What is the speed of light? Here’s the history, discovery of the cosmic speed limit

Time travel is one of the most intriguing topics in science.

On one hand, the speed of light is just a number: 299,792,458 meters per second. And on the other, it’s one of the most important constants that appears in nature and defines the relationship of causality itself.

As far as we can measure, it is a constant. It is the same speed for every observer in the entire universe. This constancy was first established in the late 1800’s with the experiments of Albert Michelson and Edward Morley at Case Western Reserve University . They attempted to measure changes in the speed of light as the Earth orbited around the Sun. They found no such variation, and no experiment ever since then has either.

Observations of the cosmic microwave background, the light released when the universe was 380,000 years old, show that the speed of light hasn’t measurably changed in over 13.8 billion years.

In fact, we now define the speed of light to be a constant, with a precise speed of 299,792,458 meters per second. While it remains a remote possibility in deeply theoretical physics that light may not be a constant, for all known purposes it is a constant, so it’s better to just define it and move on with life.

How was the speed of light first measured?

In 1676 the Danish astronomer Ole Christensen Romer made the first quantitative measurement of how fast light travels. He carefully observed the orbit of Io, the innermost moon of Jupiter. As the Earth circles the Sun in its own orbit, sometimes it approaches Jupiter and sometimes it recedes away from it. When the Earth is approaching Jupiter, the path that light has to travel from Io is shorter than when the Earth is receding away from Jupiter. By carefully measuring the changes to Io’s orbital period, Romer calculated a speed of light of around 220,000 kilometers per second.

Observations continued to improve until by the 19 th century astronomers and physicists had developed the sophistication to get very close to the modern value. In 1865, James Clerk Maxwell made a remarkable discovery. He was investigating the properties of electricity and magnetism, which for decades had remained mysterious in unconnected laboratory experiments around the world. Maxwell found that electricity and magnetism were really two sides of the same coin, both manifestations of a single electromagnetic force.

James Clerk Maxwell contributed greatly to the discover of the speed of light.

As Maxwell explored the consequences of his new theory, he found that changing magnetic fields can lead to changing electric fields, which then lead to a new round of changing magnetic fields. The fields leapfrog over each other and can even travel through empty space. When Maxwell went to calculate the speed of these electromagnetic waves, he was surprised to see the speed of light pop out – the first theoretical calculation of this important number.

What is the most precise measurement of the speed of light?

Because it is defined to be a constant, there’s no need to measure it further. The number we’ve defined is it, with no uncertainty, no error bars. It’s done. But the speed of light is just that – a speed. The number we choose to represent it depends on the units we use: kilometers versus miles, seconds versus hours, and so on. In fact, physicists commonly just set the speed of light to be 1 to make their calculations easier. So instead of trying to measure the speed light travels, physicists turn to more precisely measuring other units, like the length of the meter or the duration of the second. In other words, the defined value of the speed of light is used to establish the length of other units like the meter.

How does light slow down?

Yes, the speed of light is always a constant. But it slows down whenever it travels through a medium like air or water. How does this work? There are a few different ways to present an answer to this question, depending on whether you prefer a particle-like picture or a wave-like picture.

In a particle-like picture, light is made of tiny little bullets called photons. All those photons always travel at the speed of light, but as light passes through a medium those photons get all tangled up, bouncing around among all the molecules of the medium. This slows down the overall propagation of light, because it takes more time for the group of photons to make it through.

In a wave-like picture, light is made of electromagnetic waves. When these waves pass through a medium, they get all the charged particles in motion, which in turn generate new electromagnetic waves of their own. These interfere with the original light, forcing it to slow down as it passes through.

Either way, light always travels at the same speed, but matter can interfere with its travel, making it slow down.

Why is the speed of light important?

The speed of light is important because it’s about way more than, well, the speed of light. In the early 1900’s Einstein realized just how special this speed is. The old physics, dominated by the work of Isaac Newton, said that the universe had a fixed reference frame from which we could measure all motion. This is why Michelson and Morley went looking for changes in the speed, because it should change depending on our point of view. But their experiments showed that the speed was always constant, so what gives?

Einstein decided to take this experiment at face value. He assumed that the speed of light is a true, fundamental constant. No matter where you are, no matter how fast you’re moving, you’ll always see the same speed.

This is wild to think about. If you’re traveling at 99% the speed of light and turn on a flashlight, the beam will race ahead of you at…exactly the speed of light, no more, no less. If you’re coming from the opposite direction, you’ll still also measure the exact same speed.

This constancy forms the basis of Einstein’s special theory of relativity, which tells us that while all motion is relative – different observers won’t always agree on the length of measurements or the duration of events – some things are truly universal, like the speed of light.

Can you go faster than light speed?

Nope. Nothing can. Any particle with zero mass must travel at light speed. But anything with mass (which is most of the universe) cannot. The problem is relativity. The faster you go, the more energy you have. But we know from Einstein’s relativity that energy and mass are the same thing. So the more energy you have, the more mass you have, which makes it harder for you to go even faster. You can get as close as you want to the speed of light, but to actually crack that barrier takes an infinite amount of energy. So don’t even try.

How is the speed at which light travels related to causality?

If you think you can find a cheat to get around the limitations of light speed, then I need to tell you about its role in special relativity. You see, it’s not just about light. It just so happens that light travels at this special speed, and it was the first thing we discovered to travel at this speed. So it could have had another name. Indeed, a better name for this speed might be “the speed of time.”

Related: Is time travel possible? An astrophysicist explains

We live in a universe of causes and effects. All effects are preceded by a cause, and all causes lead to effects. The speed of light limits how quickly causes can lead to effects. Because it’s a maximum speed limit for any motion or interaction, in a given amount of time there’s a limit to what I can influence. If I want to tap you on the shoulder and you’re right next to me, I can do it right away. But if you’re on the other side of the planet, I have to travel there first. The motion of me traveling to you is limited by the speed of light, so that sets how quickly I can tap you on the shoulder – the speed light travels dictates how quickly a single cause can create an effect.

The ability to go faster than light would allow effects to happen before their causes. In essence, time travel into the past would be possible with faster-than-light travel. Since we view time as the unbroken chain of causes and effects going from the past to the future, breaking the speed of light would break causality, which would seriously undermine our sense of the forward motion of time.

Why does light travel at this speed?

No clue. It appears to us as a fundamental constant of nature. We have no theory of physics that explains its existence or why it has the value that it does. We hope that a future understanding of nature will provide this explanation, but right now all investigations are purely theoretical. For now, we just have to take it as a given.

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Speed of Light Calculator

Table of contents

With this speed of light calculator, we aim to help you calculate the distance light can travel in a fixed time . As the speed of light is the fastest speed in the universe, it would be fascinating to know just how far it can travel in a short amount of time.

We have written this article to help you understand what the speed of light is , how fast the speed of light is , and how to calculate the speed of light . We will also demonstrate some examples to help you understand the computation of the speed of light.

What is the speed of light? How fast is the speed of light?

The speed of light is scientifically proven to be the universe's maximum speed. This means no matter how hard you try, you can never exceed this speed in this universe. Hence, there are also some theories on getting into another universe by breaking this limit. You can understand this more using our speed calculator and distance calculator .

So, how fast is the speed of light? The speed of light is 299,792,458 m/s in a vacuum. The speed of light in mph is 670,616,629 mph . With this speed, one can go around the globe more than 400,000 times in a minute!

One thing to note is that the speed of light slows down when it goes through different mediums. Light travels faster in air than in water, for instance. This phenomenon causes the refraction of light.

Now, let's look at how to calculate the speed of light.

How to calculate the speed of light?

As the speed of light is constant, calculating the speed of light usually falls on calculating the distance that light can travel in a certain time period. Hence, let's have a look at the following example:

  • Source: Light
  • Speed of light: 299,792,458 m/s
  • Time traveled: 100 seconds

You can perform the calculation in three steps:

Determine the speed of light.

As mentioned, the speed of light is the fastest speed in the universe, and it is always a constant in a vacuum. Hence, the speed of light is 299,792,458 m/s .

Determine the time that the light has traveled.

The next step is to know how much time the light has traveled. Unlike looking at the speed of a sports car or a train, the speed of light is extremely fast, so the time interval that we look at is usually measured in seconds instead of minutes and hours. You can use our time lapse calculator to help you with this calculation.

For this example, the time that the light has traveled is 100 seconds .

Calculate the distance that the light has traveled.

The final step is to calculate the total distance that the light has traveled within the time . You can calculate this answer using the speed of light formula:

distance = speed of light × time

Thus, the distance that the light can travel in 100 seconds is 299,792,458 m/s × 100 seconds = 29,979,245,800 m

What is the speed of light in mph when it is in a vacuum?

The speed of light in a vacuum is 670,616,629 mph . This is equivalent to 299,792,458 m/s or 1,079,252,849 km/h. This is the fastest speed in the universe.

Is the speed of light always constant?

Yes , the speed of light is always constant for a given medium. The speed of light changes when going through different mediums. For example, light travels slower in water than in air.

How can I calculate the speed of light?

You can calculate the speed of light in three steps:

Determine the distance the light has traveled.

Apply the speed of light formula :

speed of light = distance / time

How far can the speed of light travel in 1 minute?

Light can travel 17,987,547,480 m in 1 minute . This means that light can travel around the earth more than 448 times in a minute.

Speed of light

The speed of light in the medium. In a vacuum, the speed of light is 299,792,458 m/s.

Expert Voices

Why is the speed of light the way it is?

It's just plain weird.

Einstein's theory of special relativity tells us the speed of light is 186,000 miles per second (300 million meters per second).

Paul M. Sutter is an astrophysicist at SUNY Stony Brook and the Flatiron Institute, host of Ask a Spaceman and Space Radio , and author of " How to Die in Space ." He contributed this article to Space.com's Expert Voices: Op-Ed & Insights . 

We all know and love the speed of light — 299,792,458 meters per second — but why does it have the value that it does? Why isn't it some other number? And why do we care so much about some random speed of electromagnetic waves? Why did it become such a cornerstone of physics? 

Well, it's because the speed of light is just plain weird.

Related: Constant speed of light: Einstein's special relativity survives a high-energy test

Putting light to the test

The first person to realize that light does indeed have a speed at all was an astronomer by the name of Ole Romer. In the late 1600s, he was obsessed with some strange motions of the moon Io around Jupiter. Every once in a while, the great planet would block our view of its little moon, causing an eclipse, but the timing between eclipses seemed to change over the course of the year. Either something funky was happening with the orbit of Io — which seemed suspicious — or something else was afoot.

After a couple years of observations, Romer made the connection. When we see Io get eclipsed, we're in a certain position in our own orbit around the sun. But by the next time we see another eclipse, a few days later, we're in a slightly different position, maybe closer or farther away from Jupiter than the last time. If we are farther away than the last time we saw an eclipse, then that means we have to wait a little bit of extra time to see the next one because it takes that much longer for the light to reach us, and the reverse is true if we happen to be a little bit closer to Jupiter.

The only way to explain the variations in the timing of eclipses of Io is if light has a finite speed.

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Making it mean something

Continued measurements over the course of the next few centuries solidified the measurement of the speed of light, but it wasn't until the mid-1800s when things really started to come together. That's when the physicist James Clerk Maxwell accidentally invented light.

Maxwell had been playing around with the then-poorly-understood phenomena of electricity and magnetism when he discovered a single unified picture that could explain all the disparate observations. Laying the groundwork for what we now understand to be the electromagnetic force , in those equations he discovered that changing electric fields can create magnetic fields, and vice versa. This allows waves of electricity to create waves of magnetism, which go on to make waves of electricity and back and forth and back and forth, leapfrogging over each other, capable of traveling through space.

And when he went to calculate the speed of these so-called electromagnetic waves, Maxwell got the same number that scientists had been measuring as the speed of light for centuries. Ergo, light is made of electromagnetic waves and it travels at that speed, because that is exactly how quickly waves of electricity and magnetism travel through space.

And this was all well and good until Einstein came along a few decades later and realized that the speed of light had nothing to do with light at all. With his special theory of relativity , Einstein realized the true connection between time and space, a unified fabric known as space-time. But as we all know, space is very different than time. A meter or a foot is very different than a second or a year. They appear to be two completely different things.

So how could they possibly be on the same footing?

There needed to be some sort of glue, some connection that allowed us to translate between movement in space and movement in time. In other words, we need to know how much one meter of space, for example, is worth in time. What's the exchange rate? Einstein found that there was a single constant, a certain speed, that could tell us how much space was equivalent to how much time, and vice versa.

Einstein's theories didn't say what that number was, but then he applied special relativity to the old equations of Maxwell and found that this conversion rate is exactly the speed of light.

Of course, this conversion rate, this fundamental constant that unifies space and time, doesn't know what an electromagnetic wave is, and it doesn't even really care. It's just some number, but it turns out that Maxwell had already calculated this number and discovered it without even knowing it. That's because all massless particles are able to travel at this speed, and since light is massless, it can travel at that speed. And so, the speed of light became an important cornerstone of modern physics.

But still, why that number, with that value, and not some other random number? Why did nature pick that one and no other? What's going on?

Related: The genius of Albert Einstein: his life, theories and impact on science

Making it meaningless

Well, the number doesn't really matter. It has units after all: meters per second. And in physics any number that has units attached to it can have any old value it wants, because it means you have to define what the units are. For example, in order to express the speed of light in meters per second, first you need to decide what the heck a meter is and what the heck a second is. And so the definition of the speed of light is tied up with the definitions of length and time.

In physics, we're more concerned with constants that have no units or dimensions — in other words, constants that appear in our physical theories that are just plain numbers. These appear much more fundamental, because they don't depend on any other definition. Another way of saying it is that, if we were to meet some alien civilization , we would have no way of understanding their measurement of the speed of light, but when it comes to dimensionless constants, we can all agree. They're just numbers.

One such number is known as the fine structure constant, which is a combination of the speed of light, Planck's constant , and something known as the permittivity of free space. Its value is approximately 0.007. 0.007 what? Just 0.007. Like I said, it's just a number.

So on one hand, the speed of light can be whatever it wants to be, because it has units and we need to define the units. But on the other hand, the speed of light can't be anything other than exactly what it is, because if you were to change the speed of light, you would change the fine structure constant. But our universe has chosen the fine structure constant to be approximately 0.007, and nothing else. That is simply the universe we live in, and we get no choice about it at all. And since this is fixed and universal, the speed of light has to be exactly what it is.

So why is the fine structure constant exactly the number that it is, and not something else? Good question. We don't know.

Learn more by listening to the episode "Why is the speed of light the way it is?" on the Ask A Spaceman podcast, available on iTunes and on the Web at http://www.askaspaceman.com. Thanks to Robert H, Michael E., @DesRon94, Evan W., Harry A., @twdixon, Hein P., Colin E., and Lothian53 for the questions that led to this piece! Ask your own question on Twitter using #AskASpaceman or by following Paul @PaulMattSutter and facebook.com/PaulMattSutter.

Join our Space Forums to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at: [email protected].

Paul M. Sutter is an astrophysicist at SUNY Stony Brook and the Flatiron Institute in New York City. Paul received his PhD in Physics from the University of Illinois at Urbana-Champaign in 2011, and spent three years at the Paris Institute of Astrophysics, followed by a research fellowship in Trieste, Italy, His research focuses on many diverse topics, from the emptiest regions of the universe to the earliest moments of the Big Bang to the hunt for the first stars. As an "Agent to the Stars," Paul has passionately engaged the public in science outreach for several years. He is the host of the popular "Ask a Spaceman!" podcast, author of "Your Place in the Universe" and "How to Die in Space" and he frequently appears on TV — including on The Weather Channel, for which he serves as Official Space Specialist.

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  • voidpotentialenergy This is just my opinion but i think L speed is it's speed because the particle part of it is the fastest it can interact with the quanta distance in quantum fluctuation. Light is particle and wave so the wave happens in the void between quanta. Gravity probably travels in that void and why gravity seems instant. Reply
  • rod The space.com article wraps up the discussion with, "So on one hand, the speed of light can be whatever it wants to be, because it has units and we need to define the units. But on the other hand, the speed of light can't be anything other than exactly what it is, because if you were to change the speed of light, you would change the fine structure constant. But our universe has chosen the fine structure constant to be approximately 0.007, and nothing else. That is simply the universe we live in, and we get no choice about it at all. And since this is fixed and universal, the speed of light has to be exactly what it is. So why is the fine structure constant exactly the number that it is, and not something else? Good question. We don't know." It seems that the *universe* made this decision, *But our universe has chosen the fine structure constant to be...* I did not know that the universe was capable of making decisions concerning constants used in physics. E=mc^2 is a serious constant. Look at nuclear weapons development, explosive yields, and stellar evolution burn rates for p-p chain and CNO fusion rates. The report indicates why alpha (fine structure constant) is what it is and c is what it is, *We don't know*. Reply
Admin said: We all know and love the speed of light, but why does it have the value that it does? Why isn't it some other number? And why did it become such a cornerstone of physics? Why is the speed of light the way it is? : Read more
rod said: The space.com article wraps up the discussion with, "So on one hand, the speed of light can be whatever it wants to be, because it has units and we need to define the units. But on the other hand, the speed of light can't be anything other than exactly what it is, because if you were to change the speed of light, you would change the fine structure constant. But our universe has chosen the fine structure constant to be approximately 0.007, and nothing else. That is simply the universe we live in, and we get no choice about it at all. And since this is fixed and universal, the speed of light has to be exactly what it is. So why is the fine structure constant exactly the number that it is, and not something else? Good question. We don't know." It seems that the *universe* made this decision, *But our universe has chosen the fine structure constant to be...* I did not know that the universe was capable of making decisions concerning constants used in physics. E=mc^2 is a serious constant. Look at nuclear weapons development, explosive yields, and stellar evolution burn rates for p-p chain and CNO fusion rates. The report indicates why alpha (fine structure constant) is what it is and c is what it is, *We don't know*.
  • rod FYI. When someone says *the universe has chosen*, I am reminded of these five lessons from a 1982 Fed. court trial. The essential characteristics of science are: It is guided by natural law; It has to be explanatory by reference to natural law; It is testable against the empirical world; Its conclusions are tentative, i.e., are not necessarily the final word; and It is falsifiable. Five important points about science. Reply
  • Gary If the universe is expanding , how can the speed of light be constant ( miles per second , if each mile is getting longer ) ? Can light's velocity be constant while the universe expands ? So, with the expansion of the universe , doesn't the speed of light need to increase in order to stay at a constant velocity in miles per second ? Or, do the miles in the universe remain the same length as the universe 'adds' miles to its diameter ? Are the miles lengthening or are they simply being added / compounded ? Reply
  • Gary Lets say we're in outer space and we shoot a laser through a block of glass. What causes the speed of the laser light to return to the speed it held prior to entering the block of glass ? Is there some medium in the vacuum of space that governs the speed of light ? Do the atoms in the glass push it back up to its original speed. If so, why don't those same atoms constantly push the light while it travels through the block of glass ? Reply
Gary said: Lets say we're in outer space and we shoot a laser through a block of glass. What causes the speed of the laser light to return to the speed it held prior to entering the block of glass ? Is there some medium in the vacuum of space that governs the speed of light ? Do the atoms in the glass push it back up to its original speed. If so, why don't those same atoms constantly push the light while it travels through the block of glass ?
Gary said: If the universe is expanding , how can the speed of light be constant ( miles per second , if each mile is getting longer ) ? Can light's velocity be constant while the universe expands ? So, with the expansion of the universe , doesn't the speed of light need to increase in order to stay at a constant velocity in miles per second ? Or, do the miles in the universe remain the same length as the universe 'adds' miles to its diameter ? Are the miles lengthening or are they simply being added / compounded ?
  • View All 31 Comments

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light travel speed

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light travel speed

What is the Speed of Light?

Since ancient times, philosophers and scholars have sought to understand light. In addition to trying to discern its basic properties (i.e. what is it made of – particle or wave, etc.) they have also sought to make finite measurements of how fast it travels. Since the late-17th century, scientists have been doing just that, and with increasing accuracy.

In so doing, they have gained a better understanding of light’s mechanics and the important role it plays in physics, astronomy and cosmology. Put simply, light moves at incredible speeds and is the fastest moving thing in the Universe. Its speed is considered a constant and an unbreakable barrier, and is used as a means of measuring distance. But just how fast does it travel?

Speed of Light ( c ):

Light travels at a constant speed of 1,079,252,848.8 (1.07 billion) km per hour. That works out to 299,792,458 m/s, or about 670,616,629 mph (miles per hour). To put that in perspective, if you could travel at the speed of light, you would be able to circumnavigate the globe approximately seven and a half times in one second. Meanwhile, a person flying at an average speed of about 800 km/h (500 mph), would take over 50 hours to circle the planet just once.

Illustration showing the distance between Earth and the Sun. Credit: LucasVB/Public Domain

To put that into an astronomical perspective, the average distance from the Earth to the Moon is 384,398.25 km (238,854 miles ). So light crosses that distance in about a second. Meanwhile, the average distance from the Sun to the Earth is ~149,597,886 km (92,955,817 miles), which means that light only takes about 8 minutes to make that journey.

Little wonder then why the speed of light is the metric used to determine astronomical distances. When we say a star like Proxima Centauri is 4.25 light years away, we are saying that it would take – traveling at a constant speed of 1.07 billion km per hour (670,616,629 mph) – about 4 years and 3 months to get there. But just how did we arrive at this highly specific measurement for “light-speed”?

History of Study:

Until the 17th century, scholars were unsure whether light traveled at a finite speed or instantaneously. From the days of the ancient Greeks to medieval Islamic scholars and scientists of the early modern period, the debate went back and forth. It was not until the work of Danish astronomer Øle Rømer (1644-1710) that the first quantitative measurement was made.

In 1676, Rømer observed that the periods of Jupiter’s innermost moon Io appeared to be shorter when the Earth was approaching Jupiter than when it was receding from it. From this, he concluded that light travels at a finite speed, and estimated that it takes about 22 minutes to cross the diameter of Earth’s orbit.

Prof. Albert Einstein uses the blackboard as he delivers the 11th Josiah Willard Gibbs lecture at the meeting of the American Association for the Advancement of Science in the auditorium of the Carnegie Institue of Technology Little Theater at Pittsburgh, Pa., on Dec. 28, 1934. Using three symbols, for matter, energy and the speed of light respectively, Einstein offers additional proof of a theorem propounded by him in 1905 that matter and energy are the same thing in different forms. (AP Photo)

Christiaan Huygens used this estimate and combined it with an estimate of the diameter of the Earth’s orbit to obtain an estimate of 220,000 km/s. Isaac Newton also spoke about Rømer’s calculations in his seminal work Opticks (1706). Adjusting for the distance between the Earth and the Sun, he calculated that it would take light seven or eight minutes to travel from one to the other. In both cases, they were off by a relatively small margin.

Later measurements made by French physicists Hippolyte Fizeau (1819 – 1896) and Léon Foucault (1819 – 1868) refined these measurements further – resulting in a value of 315,000 km/s (192,625 mi/s) . And by the latter half of the 19th century, scientists became aware of the connection between light and electromagnetism.

This was accomplished by physicists measuring electromagnetic and electrostatic charges, who then found that the numerical value was very close to the speed of light (as measured by Fizeau). Based on his own work, which showed that electromagnetic waves propagate in empty space, German physicist Wilhelm Eduard Weber proposed that light was an electromagnetic wave.

The next great breakthrough came during the early 20th century/ In his 1905 paper, titled “ On the Electrodynamics of Moving Bodies”, Albert Einstein asserted that the speed of light in a vacuum, measured by a non-accelerating observer, is the same in all inertial reference frames and independent of the motion of the source or observer.

A laser shining through a glass of water demonstrates how many changes in speed it undergoes - from 186,222 mph in air to 124,275 mph through the glass. It speeds up again to 140,430 mph in water, slows again through glass and then speeds up again when leaving the glass and continuing through the air. Credit: Bob King

Using this and Galileo’s principle of relativity as a basis, Einstein derived the Theory of Special Relativity , in which the speed of light in vacuum ( c ) was a fundamental constant. Prior to this, the working consensus among scientists held that space was filled with a “luminiferous aether” that was responsible for its propagation – i.e. that light traveling through a moving medium would be dragged along by the medium.

This in turn meant that the measured speed of the light would be a simple sum of its speed through the medium plus the speed of that medium. However, Einstein’s theory effectively  made the concept of the stationary aether useless and revolutionized the concepts of space and time.

Not only did it advance the idea that the speed of light is the same in all inertial reference frames, it also introduced the idea that major changes occur when things move close the speed of light. These include the time-space frame of a moving body appearing to slow down and contract in the direction of motion when measured in the frame of the observer (i.e. time dilation, where time slows as the speed of light approaches).

His observations also reconciled Maxwell’s equations for electricity and magnetism with the laws of mechanics, simplified the mathematical calculations by doing away with extraneous explanations used by other scientists, and accorded with the directly observed speed of light.

During the second half of the 20th century, increasingly accurate measurements using laser inferometers and cavity resonance techniques would further refine estimates of the speed of light. By 1972, a group at the US National Bureau of Standards in Boulder, Colorado, used the laser inferometer technique to get the currently-recognized value of 299,792,458 m/s .

Role in Modern Astrophysics:

Einstein’s theory that the speed of light in vacuum is independent of the motion of the source and the inertial reference frame of the observer has since been consistently confirmed by many experiments. It also sets an upper limit on the speeds at which all massless particles and waves (which includes light) can travel in a vacuum.

One of the outgrowths of this is that cosmologists now treat space and time as a single, unified structure known as spacetime – in which the speed of light can be used to define values for both (i.e. “lightyears”, “light minutes”, and “light seconds”). The measurement of the speed of light has also become a major factor when determining the rate of cosmic expansion.

Beginning in the 1920’s with observations of Lemaitre and Hubble, scientists and astronomers became aware that the Universe is expanding from a point of origin. Hubble also observed that the farther away a galaxy is, the faster it appears to be moving. In what is now referred to as the Hubble Parameter , the speed at which the Universe is expanding is calculated to 68 km/s per megaparsec.

This phenomena, which has been theorized to mean that some galaxies could actually be moving faster than the speed of light , may place a limit on what is observable in our Universe. Essentially, galaxies traveling faster than the speed of light would cross a “cosmological event horizon”, where they are no longer visible to us.

Also, by the 1990’s, redshift measurements of distant galaxies showed that the expansion of the Universe has been accelerating for the past few billion years. This has led to theories like “ Dark Energy “, where an unseen force is driving the expansion of space itself instead of objects moving through it (thus not placing constraints on the speed of light or violating relativity).

Along with special and general relativity, the modern value of the speed of light in a vacuum has gone on to inform cosmology, quantum physics, and the Standard Model of particle physics. It remains a constant when talking about the upper limit at which massless particles can travel, and remains an unachievable barrier for particles that have mass.

Perhaps, someday, we will find a way to exceed the speed of light. While we have no practical ideas for how this might happen, the smart money seems to be on technologies that will allow us to circumvent the laws of spacetime, either by creating warp bubbles (aka. the Alcubierre Warp Drive ), or tunneling through it (aka. wormholes ).

Until that time, we will just have to be satisfied with the Universe we can see, and to stick to exploring the part of it that is reachable using conventional methods.

We have written many articles about the speed of light for Universe Today. Here’s How Fast is the Speed of Light? , How are Galaxies Moving Away Faster than Light? , How Can Space Travel Faster than the Speed of Light? , and Breaking the Speed of Light .

Here’s a cool calculator that lets you convert many different units for the speed of light , and here’s a relativity calculator , in case you wanted to travel nearly the speed of light.

Astronomy Cast also has an episode that addresses questions about the speed of light – Questions Show: Relativity, Relativity, and more Relativity .

  • Wikipedia – Speed of Light
  • The Physics of the Universe – Speed of Light and the Principle of Relativity
  • NASA – What is the Speed of Light?
  • Galileo and Einstein – The Speed of Light

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28 Replies to “What is the Speed of Light?”

This was a really good article, Frasier. Nice review of the history, and broken down in a way regular people can understand. Great job.

Travel Light (October, 2012 – Pat Lueck)

They are born travelers… these little photons, Zipping away from their creation.

Weighing nothing, it takes nothing to speed them on their way

They don’t dally, they don’t dither. Choosing the most likely path, guided by quantum probability.

Straight across the universe, pausing only for an observation, they carry past and future within.

Oh, little photons… If only we could follow you… see your trajectory.

To you, your universe wide trip is just a “timeless blip,” no time, no wait, just zip!

The great mystery.

The photon begs the question:

What creates your cosmic speed limit? What universal traffic cop waves you through at such a constant rate?

Newly dedicated to Neil Degrasse Tyson

Thanks, I liked your piece very much.

Thanks for this article Frasier, and for helping my uneducated and average intelligence brain / mind obtain at least the tiniest inkling of understanding regarding light and the concept of spacetime.

I am now left thinking about the source of light and where it originates from, so will have to do some homework I guess. 🙂

If you understand light speed, you will understand why this makes sense: Why can’t you travel faster than the speed of light? Because you can’t travel slower than the speed of light.

Fascinated by all the comments here. Am I right in thinking that there may be space in the expanding universe that is without light…

It’s kind of funny. I have watched any number of programs and read numerous books on Einstein’s theories, as well as taking in similar material on the universe, light, space travel, etc. I ‘get’ the limitations of the energy involved trying to move mass closer and closer to the speed of light, but one thing I’ve always asked myself, and yet to see explained, is what actually limits the speed of light. I mean, photons actually have no mass, right, so what is the speed limiter, the breaking mechanism, that says to a photon “hey buddy, that’s it for you, 186,000 miles per second is your limit.” In a vacuum, with no mass, shouldn’t the speed of light in theory be infinite, even though I obviously know that’s not the case? What am I missing? This article is a case in point. It talks about the science involved in nailing down the exact speed, and goes to great lengths to describe Einstein’s theories on how light always remains a constant, contrary to former thoughts on the matter. But nowhere does it state WHY it’s set at that particular constant. Why not 90,000 miles per second, or 300,000 miles?

I, too have wondered about this for a long, long time. See my little poem prior to this post. For many years I believed that the presence of an “ether” was firmly dismissed. However, my amateur studies of “space..” have led me to believe that “space” HAS an ether-like property. Fields? Quantum Nature of space? Interaction with dark energy? Very confusing. I have read that “fields” (one for each particle.. !) exist in space, that the wave-like nature of light requires interaction with ‘something,’ and that the energy ‘field’ at every point in space acts like an ether, etc, etc.

I plan to read a lot this winter and take some serious notes. I am NOT a mathematician, but I have a keen mind for analogy creation. Teacher.

Basically, c is what it is because the electric permittivity and magnetic permeability of free space have the specific values that they do.

@timbo59 Your question boils down to: Why does 1 = 1?

The best answer I can give is found in “Beyond Einstein: non-local physics” by Brian Fraser (2015) which states: “And so we discover that the Universe not only has built in mathematics (enough of a mystery), it also has built in unit quantities.” Apparently, all fundamental equations in physics reduce to 1 = 1. The examples given in the article include Newton’s gravitation, Einstein’s mass-energy relation, and the gamma correction factor.

The free 22 page paper can be downloaded from: http://scripturalphysics.org/4v4a/BeyondEinstein.html The .html file gives a link to the .pdf file but the former has additional information, and many more links and insights.

First let me start by saying this article was a great read. Thank you for writing and posting it. I’m no scientist, but in my mind it seems as though if we could somehow capture light we could use it to propel an object. Does light exert a force on an object it runs into? That is a real question, to which I have no answer. If it does then if a large enough object that had sufficiently low mass was placed in front of a light in a vacuum it would move it right? Again, I’m not a scientist, I don’t profess to understand any of this, they are just questions from a simple mind. Thanks.

Light absolutely does exert a force on objects. Though they have zero invariant mass, photons do carry momentum, and can transfer it in interactions with other objects. This is called ‘radiation pressure’, and is the entire basis for the design of solar sails.

Minor details to fix: in picture – mps and not mph.

This is a good article but thee is no smart money on circumventing the speed of light. That is the most immutable law of this universe. Or perhaps you could suggest that dark energy and dark matter are those moving through our universe at supra-C?

What do “Black Holes” and “Dark Matter” have in common? Both of them are indicative that light changes into a form which is neither matter or light and/or evolves into either matter or light in gradations based upon the physical environment in which it is found. Thus, light might not escape “Black Holes” because of the intense gravity in the same but because light, itself, has been altered into another physical form because of the physical environment of the “black hole”, itself. Thus, the preponderance of “dark matter” in the Universe might be explained in this same context. The speed of light, the expansion of the universe, and the “big bang” might, also, be explained in light of the aforementioned.

Good article. There is one aspect of the speed of light that is rarely if ever discussed and that is why can’t rest matter be accelerated, which isn’t the equivalent of space expansion, beyond the speed of light. It turns out that its due to the time dilation effect that Einstein described with the famous Lorentz Transformation. You see momentum is conveyed through force carriers which are field photons which move at the speed of light. As a body is accelerated the path of the force carriers to convey momentum are lengthen which lowers the rate of increased velocity per unit of time(seconds) from acceleration. As the body is accelerated closer to the speed of light the force carrier paths are so long that there comes a point where the rate of velocity increase is very very small. Ultimately the force carrier paths get stretched so long that a body never reaches the speed of light but can only get close to it.

http://vixra.org/pdf/1303.0201v1.pdf Invariance of the speed of light in free space.

Although this was a good synopsis of the conventional view of light, there are a few points that need to be made in understanding the actual physical mechanism responsible for its velocity. Actually, photons do have a finite, though miniscule, mass depending on their specific energy. The definition of zero mass was given when atomic electron orbital transitions became too cumbersome in calculating atomic mass . The “negligible” photon mass could be eliminated, simplifying the atomic mass calculations Also, antenna reception of EM waves should clarify how the dual charges are inherent in photons. These rotating charges average to zero charge per cycle, but the dynamics of the photon depend on the interaction of these charges. A finding at the LANL plasma research facility was announced at the Los Alamos International Atomic Physics Summerschool class in 1989 that opposite charges interact at right angles, inducing a spin which keeps the charges at a specific distance when balanced against the attraction of opposite charges. Equal charges (with equal finite mass) would perfectly balance, resulting in a specific wavelength depending on the photon energy.

Photons have zero invariant mass, at least as far as theory and experiment can tell (well, experiment can only really set an upper limit, of course, but is consistent with it being vanishingly small).

Tach One is the speed of light Extra Terrestrials create the star systems and planets similar to how Humans create housing developments. Extra Terrestrials place the humans on Earth and live among them as Humanoid Extra Terrestrials. Humanoid Extra Terrestrials have lived here the whole time. Millions of the most famous, powerful, wealthy etc.. people living on the planet are Humanoid Extra Terrestrials and most Earthlings aren’t even aware this is a possibility. Notice how this is not even given any consideration by all the so called experts of the “ET” search. The even funnier part is when all the Earthlings wake up and realize those vehicles transiting our star system aren’t even FLYING and we call them Unidentified Flying Objects. The Earthlings are in for a rude awakening one day.

Sound waves, their speed is relative to the air. Light “waves”, their speed is relative to the aether. Really. weinsteinsletter.weebly.com Or do you think that light travels at “c” relative to a moving car and its stationary tracks? (Have to check for insanity.) 🙂 🙂

Light travels at c in all (vacuum) inertial frames of reference. This is kind of fundamental to special relativity.

Also, the Speed of Light is a local phenomenon as opposed to the Quantum Effects, which are non-local, e.g. Wave-Particle Duality, Superposition, Entanglement, etc.

May I respectfully point out a glaring error? In the graphic showing the speed changes as the laser light passes through various media, the speeds are shown as “mph”. I believe you intended it to read miles/sec. Please correct me if I’m wrong.

Thanks for the article Matt. I disagree with ” light moves at incredible speeds and is the fastest moving thing in the Universe”. We know that the influence of gravity moves at the same speed. Really it’s the relationship between space and time that determines the fastest possible speed in the Universe. It just happens that light moves at that fastest speed. So, it’s better to say ‘the speed that light also moves at’ – rather than ‘the speed of light’.

The speed of light is constant, if the photons moving in the universe, only where the matter is formed. This Einstein’s claim that the speed of light is the same irrespective of whether the light source is moving or stationary, relatively, there is no rationale. Imagine a stationary light source and another object that is moving away from him at lightning speed. If this object emits light toward a stationary object, it is not one of them can not see the light. What will happen if both objects are going the speed of light in the same direction and the back light is emitted, whether the first one to see the light.? Sure it will. According to Einstein this would not have happened, because the first object escapes the speed of light. Whether it is worth the Doppler effect for light? According to Einstein, no, but what is the red and blue shift?

Great article. Again. Hmm. Correct me if I’m wrong but doesn’t it take light 0 sec to reach the nearest star? It is for the observer on earth it takes 4,2 years to watch the light get to its destination. If you actually travel at the speed of light, you can go anywhere in the universe in no time. Haven’t done the math lately but I remember the figure 75 years to get to the other side of the universe with a rocket accelerating with 1g.

One thing that I’ve always wondered about the speed of light… As a computer guy, the analogy that comes to mind is networks, and the information propagation latency of packets travelling through a network. Even there, there is an absolute top limit of lightspeed, but before that, there’s the latency of the switching fabric itself. So, my question is this: In the crudest terms, is the speed of light representing the latency limits of information propagation (a photon) through the ‘switching fabric’ of whatever quantum elements constitute space-time?

It’s always been easier for me to think about this stuff in terms of a 4th spatial dimension that measures the distance between quantum bits, which I imagine increasing as gravity and/or speed increases. Thus, the macro-level structures (like atoms and people) perceive time as slowing down, due ot the propagation of information becoming slower as the density of the quantum bits decreases (or distance between the bits increases), as measured by this 4th spatial dimension.

By that logic, Gravity becomes a measure of the density of space-time in this 4th spatial dimension, which I’ve never heard mentioned anywhere, so I assume my analogy breaks down at this point 🙂

read back up the comments.. (to ‘Qev” on Sep 2). He basically answers your questions…though I have not had the time to study “…electric permittivity and magnetic permeability of free space…” Let me know if you do the research.. : ) — : )

Comments are closed.

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What Is the Speed of Light?

Speed of Light

The speed of light is the rate at which light travels. The speed of light in a vacuum is a constant value that is denoted by the letter c and is defined as exactly 299,792,458 meters per second. Visible light , other electromagnetic radiation, gravity waves, and other massless particles travel at c. Matter , which has mass, can approach the speed of light, but never reach it.

Value for the Speed of Light in Different Units

Here are values for the speed of light in various units:

  • 299,792,458 meters per second ( exact number )
  • 299,792 kilometers per second (rounded)
  • 3×10 8 m/s (rounded)
  • 186,000 miles per second (rounded)
  • 671,000,000 miles per hour (rounded)
  • 1,080,000,000 kilometers per hour (rounded)

Is the Speed of Light Really Constant?

The speed of light in a vacuum is a constant. However, scientists are exploring whether the speed of light has changed over time.

Also, the rate at which light travels changes as it passes through a medium. The index of refraction describes this change. For example, the index of refraction of water is 1.333, which means light travels 1.333 times slower in water than in a vacuum. The index of refraction of a diamond is 2.417. A diamond slows the speed of light by more than half its speed in a vacuum.

How to Measure the Speed of Light

One way of measuring the speed of light uses great distances, such as distant points on the Earth or known distances between the Earth and astronomical objects. For example, you can measure the speed of light by measuring the time it takes for light to travel from a light source to a distant mirror and back again. The other way of measuring the speed of light is solving for c in equations. Now that the speed of light is defined, it is fixed rather than measured. Measuring the speed of light today indirectly measures the length of the meter, rather than c .

In 1676, Danish astronomer Ole Rømer discovered light travels at a speed by studying the movement of Jupiter’s moon Io. Prior to this, it seemed light propagated instantaneously. For example, you see a lightning strike immediately, but don’t hear thunder until after the event . So, Rømer’s finding showed light takes time to travel, but scientists did not know the speed of light or whether it was constant. In 1865, James Clerk Maxwell proposed that light was an electromagnetic wave that travelled at a speed c . Albert Einstein suggested c was a constant and that it did not change according to the frame of reference of the observer or any motion of a light source. In other words, Einstein suggested the speed of light is invariant . Since then, numerous experiments have verified the invariance of c .

Is It Possible to Go Faster Than Light?

The upper speed limit for massless particles is c . Objects that have mass cannot travel at the speed of light or exceed it. Among other reasons, traveling at c gives an object a length of zero and infinite mass. Accelerating a mass to the speed of light requires infinite energy. Furthermore, energy, signals, and individual photos cannot travel faster than c . At first glance, quantum entanglement appears to transmit information faster than c . When two particles are entangled, changing the state of one particle instantaneously determines the state of the other particle, regardless of the distance between them. But, information cannot be transmitted instantaneously (faster than c ) because it isn’t possible to control the initial quantum state of the particle when it is observed.

However, faster-than-light speeds appear in physics. For example, the phase velocity of x-rays through glass often exceeds c. However, the information isn’t conveyed by the waves faster than the speed of light. Distant galaxies appear to move away from Earth faster than the speed of light (outside a distance called the Hubble sphere), but the motion isn’t due to the galaxies traveling through space. Instead, space itself it expanding. So again, no actual movement faster than c occurs.

While it isn’t possible to go faster than the speed of light, it doesn’t necessarily mean warp drive or other faster-than-light travel is impossible. The key to going faster than the speed of light is to change space-time. Ways this might happen include tunneling using wormholes or stretching space-time into a “warp bubble” around a spacecraft. But, so far these theories don’t have practical applications.

  • Brillouin, L. (1960). Wave Propagation and Group Velocity. Academic Press.
  • Ellis, G.F.R.; Uzan, J.-P. (2005). “‘c’ is the speed of light, isn’t it?”. American Journal of Physics . 73 (3): 240–27. doi: 10.1119/1.1819929
  • Helmcke, J.; Riehle, F. (2001). “Physics behind the definition of the meter”. In Quinn, T.J.; Leschiutta, S.; Tavella, P. (eds.). Recent advances in metrology and fundamental constants . IOS Press. p. 453. ISBN 978-1-58603-167-1.
  • Newcomb, S. (1886). “The Velocity of Light”. Nature . 34 (863): 29–32. doi: 10.1038/034029c0
  • Uzan, J.-P. (2003). “The fundamental constants and their variation: observational status and theoretical motivations”. Reviews of Modern Physics . 75 (2): 403. doi: 10.1103/RevModPhys.75.403

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Learn About the True Speed of Light and How It's Used

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Light moves through the universe at the fastest speed astronomers can measure. In fact, the speed of light is a cosmic speed limit, and nothing is known to move faster. How fast does light move? This limit can be measured and it also helps define our understanding of the universe's size and age.

What Is Light: Wave or Particle?

Light travels fast, at a velocity of 299, 792, 458 meters per second. How can it do this? To understand that, it's helpful to know what light actually is and that's largely a 20th-century discovery.

The nature of light was a great mystery for centuries. Scientists had trouble grasping the concept of its wave and particle nature. If it was a wave what did it propagate through? Why did it appear to travel at the same speed in all directions? And, what can the speed of light tell us about the cosmos? It wasn't until Albert Einstein described this theory of special relativity in 1905 it all came into focus. Einstein argued that space and time were relative and that the speed of light was the constant that connected the two.

What Is the Speed of Light?

It is often stated that the speed of light is constant and that nothing can travel faster than the speed of light. This isn't entirely accurate. The value of 299,792,458 meters per second (186,282 miles per second) is the speed of light in a vacuum. However, light actually slows down as it passes through different media. For instance, when it moves through glass, it slows down to about two-thirds of its speed in a vacuum. Even in air, which is nearly a vacuum, light slows down slightly. As it moves through space, it encounters clouds of gas and dust, as well as gravitational fields, and those can change the speed a tiny bit. The clouds of gas and dust also absorb some of the light as it passes through.

This phenomenon has to do with the nature of light, which is an electromagnetic wave. As it propagates through a material its electric and magnetic fields "disturb" the charged particles that it comes in contact with. These disturbances then cause the particles to radiate light at the same frequency, but with a phase shift. The sum of all these waves produced by the "disturbances" will lead to an electromagnetic wave with the same frequency as the original light, but with a shorter wavelength and, hence a slower speed.

Interesting, as fast as light moves, its path can be bent as it passes by regions in space with intense gravitational fields. This is fairly easily seen in galaxy clusters, which contain a lot of matter (including dark matter), which warps the path of light from more distant objects, such as quasars.

Lightspeed and Gravitational Waves

Current theories of physics predict that gravitational waves also travel at the speed of light, but this is still being confirmed as scientists study the phenomenon of gravitational waves from colliding black holes and neutron stars. Otherwise, there are no other objects that travel that fast. Theoretically, they can get close to the speed of light, but not faster.

One exception to this may be space-time itself. It appears that distant galaxies are moving away from us faster than the speed of light. This is a "problem" that scientists are still trying to understand. However, one interesting consequence of this is that a travel system based on the idea of a warp drive . In such a technology, a spacecraft is at rest relative to space and it's actually space that moves, like a surfer riding a wave on the ocean. Theoretically, this might allow for superluminal travel. Of course, there are other practical and technological limitations that stand in the way, but it's an interesting science-fiction idea that is getting some scientific interest. 

Travel Times for Light

One of the questions that astronomers get from members of the public is: "how long would it take light to go from object X to Object Y?" Light gives them a very accurate way to measure the size of the universe by defining distances. Here are a few of the common ones distance measurements:

  • The Earth to the Moon : 1.255 seconds
  • The Sun to Earth : 8.3 minutes
  • Our Sun to the next closest star : 4.24 years
  • Across our Milky Way  galaxy : 100,000 years
  • To the closest  spiral galaxy (Andromeda) : 2.5 million years
  • Limit of the observable universe to Earth : 13.8 billion years

Interestingly, there are objects that are beyond our ability to see simply because the universe IS expanding, and some are "over the horizon" beyond which we cannot see. They will never come into our view, no matter how fast their light travels. This is one of the fascinating effects of living in an expanding universe. 

Edited by Carolyn Collins Petersen

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The Nine Planets

The Nine Planets

How Fast is the Speed of Light?

With our current understanding of motion, it seems that the speed of light is the highest of all, being 874,030 times faster than the speed of sound.

The speed of sound travels at around 343 m/s, while the speed of light travels at 299,792,458 m/s. In miles per hour/mph, the speed of light is at around 670,616,629, while in kilometers per hour, light travels at 1,079,252,848.

In terms of seconds, light travels at around 300,000 kilometers per second or 186,000 miles per second in a vacuum.

light travel speed

In water, the speed of light is slower, at 225,000 km / 139,808 mi per second, and 200,000 km / 124,274 mi per second in glass. It seems that nothing can be faster than the speed of light.

If you want an example of how fast the speed of light is, think about this, if we were to launch an imaginary spacecraft from Earth that would travel at around 153,454 mi / 246,960 km per hour constantly, it would reach the Sun in 606 hours, or 25 days. 

However, if our spacecraft would be traveling at the speed of light, we would reach the Sun in only 8.3 minutes. If you traveled around the Earth with the speed of light, you would make a complete tour of our planet 7.5 times in just one second.

In theory, it seems that nothing is faster than the speed of light, or is there? Let’s find out.

Is There Anything Faster Than the Speed of Light?

It appears that nothing is faster than the speed of light, but the Universe , as always, eludes our perception once again. Scientists have demonstrated that the Universe is expanding, and this expansion is even faster than the speed of light.

Since space is theoretically “nothing,” it isn’t susceptible to the laws of physics. If you were to hold a torch and run with it, the speed of its light would still travel at the same rate.

Some galaxies are moving away from our Milky Way faster than the speed of light, and this is happening because space itself is moving along with them.

light travel speed

If there were something more efficient than traveling with the speed of light, it would be traveling through wormholes. Wormholes are hypothetical, but their mechanism is quite intriguing, and in a way, if it were possible, they are supposedly faster than the speed of light.

This is because a wormhole connects two distant points, and, in theory, if you were to travel from point a to b, regardless of its distance, you would reach your destination extremely fast.

How Fast is the Speed of Dark?

Many consider that the speed of darkness is simply a poetic metaphor and wouldn’t have any legitimate scientific basis, since dark is simply the absence of light.

However, this may seem a bit more complicated. If we were to put a dark spot in a beam of light, darkness would theoretically move at the same speed as light.

The same holds true if we would illuminate a dark corner. It is uncertain if darkness itself has a speed, but when it comes to dark matter, things start to unfold.

light travel speed

Dark matter is hypothetical energy, which makes up more than 80% of our Universe. In some studies, scientists estimated that this mysterious element might travel at around 54 m/s, to equate for its existence, but this is quite slow when compared to the speed of light.

Things get complicated if we look at black holes as part of the definition of darkness. Black holes are devoid of light, and if anything gets near their event horizon, not even light can escape from them.

Some black holes are fast-spinner as well, with some of them being recorded with having a spinning speed of around 84% of the speed of light. Darkness or the speed of dark is quite a fascinating subject, but it remains elusive to our current understanding.

What is the Fastest Thing in the Universe?

The fastest thing in the Universe, based on our current knowledge, is light. If you want to play dirty, you could say that the Universe/space is the fastest thing in existence, since it expands with a speed even faster than the speed of light.

If, in the future, we will understand how black holes can capture even light, maybe some of their mechanisms are the fastest thing in the Universe.

What Would Happen if You Would Travel Faster Than the Speed of Light?

The theory of special relativity states that nothing should travel faster than the speed of light, and if something does so, it will move backward in time.

Traveling faster than the speed of light might simply mean time travel. However, is this were true, in some ways, you might as well achieve immortality, as no cause could affect you, not even time, especially if, hypothetically speaking, you wouldn’t even be subjected to the impacts of the objects you would travel through.

light travel speed

Our current understanding of light speed is minimal, and even more so when it comes to surpassing it. We, as a species, with our current technology, have only just reached small percentages of the speed of light. We aren’t even halfway there.

What is the 2 nd Fastest Thing in the Universe?

Blobs of hot gas embedded in streams of material ejected from blazars, which are highly active galaxies , travel at around 99.9% of the speed of light.

light travel speed

Thus, the physical processes that occur at the cores of blazars are so energetic that they can propel matter quite close to light speed, and as such, they are probably the second fastest thing in the Universe. 

Did you know?

The fastest speed reached by a land vehicle is the ThrustSSC supersonic car. This vehicle reached 1,227 km / 772 mi/h, and it maintains its title as the most rapid land vehicle since 1997.

The fastest plane/aircraft in the world is the Lockheed SR-71 Black Bird. It achieved this title in 1976, and it reached a speed of 3,529.6 km/ 2,192 mi per hour.

The Parker Solar Probe is currently the fastest spacecraft ever designed by man. It reached 153,454 miles / 246,960 kilometers per hour.

Image Sources:

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How "Fast" is the Speed of Light?

Light travels at a constant, finite speed of 186,000 mi/sec. A traveler, moving at the speed of light, would circum-navigate the equator approximately 7.5 times in one second. By comparison, a traveler in a jet aircraft, moving at a ground speed of 500 mph, would cross the continental U.S. once in 4 hours.

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May 20, 2016

How does light travel?

by Matt Williams, Universe Today

How does light travel?

Ever since Democritus – a Greek philosopher who lived between the 5th and 4th century's BCE – argued that all of existence was made up of tiny indivisible atoms, scientists have been speculating as to the true nature of light. Whereas scientists ventured back and forth between the notion that light was a particle or a wave until the modern, the 20th century led to breakthroughs that showed that it behaves as both.

These included the discovery of the electron, the development of quantum theory, and Einstein's Theory of Relativity. However, there remains many fascinating and unanswered questions when it comes to light, many of which arise from its dual nature. For instance, how is it that light can be apparently without mass, but still behave as a particle? And how can it behave like a wave and pass through a vacuum, when all other waves require a medium to propagate?

Theory of Light in the 19th Century:

During the Scientific Revolution, scientists began moving away from Aristotelian scientific theories that had been seen as accepted canon for centuries. This included rejecting Aristotle's theory of light, which viewed it as being a disturbance in the air (one of his four "elements" that composed matter), and embracing the more mechanistic view that light was composed of indivisible atoms.

In many ways, this theory had been previewed by atomists of Classical Antiquity – such as Democritus and Lucretius – both of whom viewed light as a unit of matter given off by the sun. By the 17th century, several scientists emerged who accepted this view, stating that light was made up of discrete particles (or "corpuscles"). This included Pierre Gassendi, a contemporary of René Descartes, Thomas Hobbes, Robert Boyle, and most famously, Sir Isaac Newton.

Newton's corpuscular theory was an elaboration of his view of reality as an interaction of material points through forces. This theory would remain the accepted scientific view for more than 100 years, the principles of which were explained in his 1704 treatise "Opticks, or, a Treatise of the Reflections, Refractions, Inflections, and Colours of Light". According to Newton, the principles of light could be summed as follows:

  • Every source of light emits large numbers of tiny particles known as corpuscles in a medium surrounding the source.
  • These corpuscles are perfectly elastic, rigid, and weightless.

This represented a challenge to "wave theory", which had been advocated by 17th century Dutch astronomer Christiaan Huygens. . These theories were first communicated in 1678 to the Paris Academy of Sciences and were published in 1690 in his "Traité de la lumière" ("Treatise on Light"). In it, he argued a revised version of Descartes views, in which the speed of light is infinite and propagated by means of spherical waves emitted along the wave front.

Double-Slit Experiment:

By the early 19th century, scientists began to break with corpuscular theory. This was due in part to the fact that corpuscular theory failed to adequately explain the diffraction, interference and polarization of light, but was also because of various experiments that seemed to confirm the still-competing view that light behaved as a wave.

The most famous of these was arguably the Double-Slit Experiment, which was originally conducted by English polymath Thomas Young in 1801 (though Sir Isaac Newton is believed to have conducted something similar in his own time). In Young's version of the experiment, he used a slip of paper with slits cut into it, and then pointed a light source at them to measure how light passed through it.

According to classical (i.e. Newtonian) particle theory, the results of the experiment should have corresponded to the slits, the impacts on the screen appearing in two vertical lines. Instead, the results showed that the coherent beams of light were interfering, creating a pattern of bright and dark bands on the screen. This contradicted classical particle theory, in which particles do not interfere with each other, but merely collide.

The only possible explanation for this pattern of interference was that the light beams were in fact behaving as waves. Thus, this experiment dispelled the notion that light consisted of corpuscles and played a vital part in the acceptance of the wave theory of light. However subsequent research, involving the discovery of the electron and electromagnetic radiation , would lead to scientists considering yet again that light behaved as a particle too, thus giving rise to wave-particle duality theory.

Electromagnetism and Special Relativity:

Prior to the 19th and 20th centuries, the speed of light had already been determined. The first recorded measurements were performed by Danish astronomer Ole Rømer, who demonstrated in 1676 using light measurements from Jupiter's moon Io to show that light travels at a finite speed (rather than instantaneously).

By the late 19th century , James Clerk Maxwell proposed that light was an electromagnetic wave, and devised several equations (known as Maxwell's equations) to describe how electric and magnetic fields are generated and altered by each other and by charges and currents. By conducting measurements of different types of radiation (magnetic fields, ultraviolet and infrared radiation), he was able to calculate the speed of light in a vacuum (represented as c).

In 1905, Albert Einstein published "On the Electrodynamics of Moving Bodies", in which he advanced one of his most famous theories and overturned centuries of accepted notions and orthodoxies. In his paper, he postulated that the speed of light was the same in all inertial reference frames, regardless of the motion of the light source or the position of the observer.

Exploring the consequences of this theory is what led him to propose his theory of Special Relativity, which reconciled Maxwell's equations for electricity and magnetism with the laws of mechanics, simplified the mathematical calculations, and accorded with the directly observed speed of light and accounted for the observed aberrations. It also demonstrated that the speed of light had relevance outside the context of light and electromagnetism.

For one, it introduced the idea that major changes occur when things move close the speed of light, including the time-space frame of a moving body appearing to slow down and contract in the direction of motion when measured in the frame of the observer. After centuries of increasingly precise measurements, the speed of light was determined to be 299,792,458 m/s in 1975.

How does light travel?

Einstein and the Photon:

In 1905, Einstein also helped to resolve a great deal of confusion surrounding the behavior of electromagnetic radiation when he proposed that electrons are emitted from atoms when they absorb energy from light. Known as the photoelectric effect, Einstein based his idea on Planck's earlier work with "black bodies" – materials that absorb electromagnetic energy instead of reflecting it (i.e. white bodies).

At the time, Einstein's photoelectric effect was attempt to explain the "black body problem", in which a black body emits electromagnetic radiation due to the object's heat. This was a persistent problem in the world of physics, arising from the discovery of the electron, which had only happened eight years previous (thanks to British physicists led by J.J. Thompson and experiments using cathode ray tubes).

At the time, scientists still believed that electromagnetic energy behaved as a wave, and were therefore hoping to be able to explain it in terms of classical physics. Einstein's explanation represented a break with this, asserting that electromagnetic radiation behaved in ways that were consistent with a particle – a quantized form of light which he named "photons". For this discovery, Einstein was awarded the Nobel Prize in 1921.

Wave-Particle Duality:

Subsequent theories on the behavior of light would further refine this idea, which included French physicist Louis-Victor de Broglie calculating the wavelength at which light functioned. This was followed by Heisenberg's "uncertainty principle" (which stated that measuring the position of a photon accurately would disturb measurements of it momentum and vice versa), and Schrödinger's paradox that claimed that all particles have a " wave function ".

In accordance with quantum mechanical explanation, Schrodinger proposed that all the information about a particle (in this case, a photon) is encoded in its wave function, a complex-valued function roughly analogous to the amplitude of a wave at each point in space. At some location, the measurement of the wave function will randomly "collapse", or rather "decohere", to a sharply peaked function. This was illustrated in Schrödinger famous paradox involving a closed box, a cat, and a vial of poison (known as the "Schrödinger's Cat" paradox).

According to his theory, wave function also evolves according to a differential equation (aka. the Schrödinger equation). For particles with mass, this equation has solutions; but for particles with no mass, no solution existed. Further experiments involving the Double-Slit Experiment confirmed the dual nature of photons. where measuring devices were incorporated to observe the photons as they passed through the slits.

When this was done, the photons appeared in the form of particles and their impacts on the screen corresponded to the slits – tiny particle-sized spots distributed in straight vertical lines. By placing an observation device in place, the wave function of the photons collapsed and the light behaved as classical particles once more. As predicted by Schrödinger, this could only be resolved by claiming that light has a wave function, and that observing it causes the range of behavioral possibilities to collapse to the point where its behavior becomes predictable.

The development of Quantum Field Theory (QFT) was devised in the following decades to resolve much of the ambiguity around wave-particle duality. And in time, this theory was shown to apply to other particles and fundamental forces of interaction (such as weak and strong nuclear forces). Today, photons are part of the Standard Model of particle physics, where they are classified as boson – a class of subatomic particles that are force carriers and have no mass.

So how does light travel? Basically, traveling at incredible speeds (299 792 458 m/s) and at different wavelengths, depending on its energy. It also behaves as both a wave and a particle, able to propagate through mediums (like air and water) as well as space. It has no mass, but can still be absorbed, reflected, or refracted if it comes in contact with a medium. And in the end, the only thing that can truly slow down or arrest the speed of light is gravity (i.e. a black hole).

What we have learned about light and electromagnetism has been intrinsic to the revolution which took place in physics in the early 20th century, a revolution that we have been grappling with ever since. Thanks to the efforts of scientists like Maxwell, Planck, Einstein, Heisenberg and Schrodinger, we have learned much, but still have much to learn.

For instance, its interaction with gravity (along with weak and strong nuclear forces) remains a mystery. Unlocking this, and thus discovering a Theory of Everything (ToE) is something astronomers and physicists look forward to. Someday, we just might have it all figured out!

Source: Universe Today

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space traveler looking into portal on another planet

Scientists Believe Light Speed Travel Is Possible. Here’s How.

A functioning warp drive would allow humans to reach the far ends of the cosmos in the blink of an eye.

White and his team in LSI’s Houston laboratory were conducting research for the Defense Advanced Research Projects Agency, or DARPA, and had set up these particular experiments to study the energy densities within Casimir cavities, the mysterious spaces between microscopic metal plates in a vacuum. The data plot indicated areas of diminished energy between the plates, which caused them to push toward each other as if trying to fill the void. This is known as negative vacuum energy density, a phenomenon in quantum mechanics called, appropriately enough, the Casimir effect . It’s something that’s helping scientists understand the soupy physics of microscale structures, which some researchers hope can be applied to energy applications that are more practical, such as circuits and electromechanical systems.

But White noticed that the pattern of negative vacuum energy between the plates and around tiny cylindrical columns that they’d inserted in the space looked familiar. It precisely echoed the energy pattern generated by a type of exotic matter that some physicists believe could unlock high-speed interstellar travel. “We then looked, mathematically, at what happens if we placed a one-micron sphere inside of a four-micron cylinder under the same conditions, and found that this kind of structure could generate a little nanoscale warp bubble encapsulating that central region,” White explains.

That’s right—a warp bubble. The essential component of a heretofore fictional warp drive that has for decades been the obsession of physicists, engineers, and sci-fi fans. Warp drive, of course, is the stuff of Star Trek legend, a device enclosed within a spacecraft that gives the mortals aboard the ability to rip around the cosmos at superhuman speed. To the lay sci-fi fan, it’s a “black box”—a convenient, completely made-up workaround to avoid the harsh realities of interstellar travel. However, after decades of speculation, research, and experimentation, scientists believe a warp drive could actually work.

To emphasize: White didn’t actually make a warp bubble. But the data from his study led to an aha moment: For the first time, a buildable warp bubble showed promise of success.

diagram showing a negative vacuum energy in between two uncharged metallic plates

Warp technology’s core science is surprisingly sound. Though the specific mechanics of an actual device haven’t been fully unpacked, the math points toward feasibility. In short, a real-life warp drive would use massive amounts of energy, which can come in the form of mass, to create enough gravitational pull to distort spacetime in a controlled fashion, allowing a ship to speed along inside a self-generated bubble that itself is able to travel at essentially any speed. Warp drives popped up in fiction intermittently for several decades before Star Trek creator Gene Roddenberry plugged one into the USS Enterprise in 1966. But Miguel Alcubierre, PhD, a Mexican theoretical physicist and professed Star Trek enthusiast, gave the idea real-world legs when he released a paper in 1994 speculating that such a drive was mathematically possible. It was the first serious treatment of a warp drive’s feasibility, and it made headlines around the world. His breakthrough inspired more scientists to nudge the theoretical aspects of warp drive toward concrete, practical applications.

“I proposed a ‘geometry’ for space that would allow faster-than-light travel as seen from far away, essentially expanding space behind the object we want to move and contracting it in front,” Alcubierre says. “This forms a ‘bubble’ of distorted space, inside of which an object—a spaceship, say—could reside.”

Physicists tend to speak in relative terms. By injecting the sly qualifier “as seen from far away,” Alcubierre might sound like he’s describing the galactic equivalent of an optical illusion —an effect perhaps similar to driving past a truck going the opposite direction on the highway when you’re both going 60 miles an hour. Sure feels like a buck-twenty, doesn’t it? But the A-to-B speed is real; the warp effect simply shortens the literal distance between two points. You’re not, strictly speaking, moving faster than light. Inside the bubble, all appears relatively normal, and light moves faster than you are, as it should. Outside the bubble, however, you’re haulin’ the mail.

.css-1i6271r{margin:0rem;font-size:1.625rem;line-height:1.2;font-family:UnitedSans,UnitedSans-roboto,UnitedSans-local,Helvetica,Arial,Sans-serif;padding:0.9rem 1rem 1rem;}@media(max-width: 48rem){.css-1i6271r{font-size:1.75rem;line-height:1;}}@media(min-width: 48rem){.css-1i6271r{font-size:1.875rem;line-height:1;}}@media(min-width: 64rem){.css-1i6271r{font-size:2.25rem;line-height:1;}}.css-1i6271r em,.css-1i6271r i{font-style:italic;font-family:inherit;}.css-1i6271r b,.css-1i6271r strong{font-family:inherit;font-weight:bold;} THOUGH THE SPECIFIC MECHANICS OF AN ACTUAL DEVICE HAVEN’T BEEN UNPACKED, THE MATH POINTS TOWARD FEASIBILITY.

Alcubierre’s proposal had solved one of the initial hurdles to achieving warp speeds: The very idea clashes with Einstein’s long-accepted theory of general relativity, which states that nothing can travel faster than the speed of light, but it doesn’t preclude space itself from traveling faster than that. In fact, scientists speculate that the same principles explain the rapid expansion of the universe after the Big Bang .

While concluding that warp speed was indeed possible, Alcubierre also found that it would require an enormous amount of energy to sustain the warp bubble. He theorized that negative energy—the stuff hinted at by White’s experimentation with Casimir cavities—could be a solution. The only problem is that no one has yet proved that negative energy is real. It’s the unobtanium of our spacefaring imaginations, something researchers only believe to exist. In theory, however, this unknown matter may be sufficiently powerful that future warp drive designers could channel it to contract spacetime around it. In conceptual drawings of warp-capable spacecraft , enormous material rings containing this energy source surround a central fuselage. When activated, it warps spacetime around the entire ship. The more intense the warping, the faster the warp travel is achieved.

Of course, it’s not that simple. Physicist José Natário, PhD, a professor at the Instituto Superior Técnico in Lisbon, wrote his own influential paper about the mathematical feasibility of warp drives in 2001. However, he is concerned about practical conundrums, like the amount of energy required. “You need to be able to curve spacetime quite a lot in order to do this,” he says. “We’re talking about something that would be much, much more powerful than the sun.”

Alcubierre is similarly skeptical that his theoretical ideas might ever be used to develop a working warp drive. “In order to have a bubble about 100 meters wide traveling at precisely the speed of light, you would need about 100 times the mass of the planet Jupiter converted into negative energy, which of course sounds absurd,” he says. By that standard, he concludes, a warp drive is very unlikely.

example of a warp bubble where a large object of mass pulls and contracts space to create faster than light speed

Physicists love a challenge, though. In the 29 years since Alcubierre published his paper, other scientists have wrestled with the implications of the work, providing alternative approaches to generating the energy using more accessible power sources, finding oblique entry points to the problem, and batting ideas back and forth in response to one another’s papers. They use analogies involving trampolines , tablecloths, bowling balls, balloons, conveyor belts, and music to explain the physics.

They even have their own vocabulary. It’s not faster-than-light travel; it’s superluminal travel, thank you. Then there’s nonphysical and physical—a.k.a. the critical distinction between theoretical speculation and something that can actually be engineered. (Pro tip: We’re aiming for physical here, folks.) They do mention Star Trek a lot, but never Star Wars . Even the scruffiest-looking nerf herder knows that the ships in Star Wars use hyperdrive, which consumes fuel, rather than warp drives, which don’t use propulsive technology but instead rely on, well, warping. They’re also vague about details like what passengers would experience, what gravity is like on board since you’re carrying around boatloads of energy, and what would happen if someone, say, jumped out of the ship while warping. (A speculative guess: Nothing good.)

Such research isn’t typically funded by academic institutions or the DARPAs and NASAs of the world, so much of this work occurs in the scientists’ spare time. One such scientist and Star Trek enthusiast is physicist Erik Lentz, PhD. Now a researcher at Pacific Northwest National Laboratory in Richland, Washington, Lentz was doing postdoctoral work at Göttingen University in Germany when, amid the early, isolated days of the pandemic, he mulled the idea of faster-than-light travel. He published a paper in 2021 arguing that warp drives could be generated using positive energy sources instead of the negative energy that Alcubierre’s warp drive seemed to require.

“There are a number of barriers to entry to actually being able to build a warp drive,” Lentz says. “The negative energy was the most obvious, so I tried to break that barrier down.”

He explored a new class of solutions in Einstein’s general relativity while focusing on something called the weak-energy condition, which, he explains, tracks the positivity of energy in spacetime. He hit upon a “soliton solution”—a wave that maintains its shape and moves at a constant velocity—that could both satisfy the energy-level challenge and travel faster than light. Such a warp bubble could travel along using known energy sources, though harnessing those at the levels needed are still far beyond our capabilities. The next step, he notes, may be bringing the energy requirements for a warp drive to within the range of a nuclear fusion reactor.

A fusion-powered device could theoretically travel to and from Proxima Centauri , Earth’s nearest star, in years instead of decades or millennia, and then go faster and faster as power sources improve. Current conventional rocket technology, on the other hand, would take 50,000 years just for a one-way trip—assuming, of course, there was an unlimited fuel supply for those engines.

“IF YOU COLLIDE WITH SOMETHING ON YOUR PATH, IT WOULD ALMOST CERTAINLY BE CATASTROPHIC.”

Like Alcubierre’s original thesis, Lentz’s paper had a seismic impact on the warp drive community, prompting yet another group of scientists to dig into the challenge. Physicist Alexey Bobrick and technology entrepreneur Gianni Martire have been particularly prolific. In 2021, they released a paper theorizing that a class of subliminal warp drives, traveling at just a fraction of light speed, could be developed from current scientific understanding. While that paper essentially argued that it’s perfectly acceptable to walk before you can run, they followed it up with another theory earlier this year that describes how a simulated black hole , created using sound waves and glycerin and tested with a laser beam, could be used to evaluate the levels of gravitational force needed to warp spacetime. The duo coded that breakthrough into a public app that they hope will help more quickly push theoretical ideas to practical ones. Though the team is waiting for the technology to clear a peer review stage before releasing details, the app is essentially a simulator that allows scientists to enter their warp-speed equations to validate whether they’re practical.

“When somebody publishes a warp metric for the first time, people say, ‘Okay, is your metric physical?’” Martire says. The answer to that question—whether the metric has practical potential or is strictly theoretical—is hard to establish given the challenges of testing these hypotheses. That determination could take six to eight months. “Now we can tell you within seconds, and it shows you visually how off you are or how close you are,” he says.

While useful, the app will speed up the preliminary math only for future researchers. Galaxy-sized challenges remain before we ever experience turbocharged interstellar travel. Alcubierre worries in particular about what may happen near the walls of the warp bubble. The distortion of space is so violent there, he notes, that it would destroy anything that gets close. “If you collide with something on your path, it would almost certainly be catastrophic,” he says.

Natário mulls even more practical issues, like steering and stopping. “It’s a bubble of space, that you’re pushing through space,” he says. “So, you’d have to tell space ... to curve in front of your spaceship.” But therein lies the problem: You can’t signal to the space in front of you to behave the way you want it to.

His opinion? Superluminal travel is impossible. “You need these huge deformations that we have no idea how to accomplish,” Natário says. “So yes, there has been a lot of effort toward this and studying these weird solutions, but this is all still completely theoretical, abstract, and very, very, very, very far from getting anywhere near a practical warp drive.” That’s “very” to the power of four, mind you—each crushing blow pushing us exponentially, excruciatingly further and further away from our yearned-for superluminal lives.

Ultimately, the pursuit of viable high-speed interstellar transportation also points to a more pressing terrestrial challenge: how the scientific community tackles ultra-long-term challenges in the first place. Most of the research so far has come from self-starters without direct funding, or by serendipitous discoveries made while exploring often unrelated research, such as Dr. White’s work on Casimir cavities.

Many scientists argue that we’re in a multi-decade period of stagnation in physics research, and warp drive—despite its epic time horizons before initial research leads to galaxy-spanning adventures—is somewhat emblematic of that stagnation. Sabine Hossenfelder, a research fellow at the Frankfurt Institute for Advanced Studies and creator of the YouTube channel Science Without the Gobbledygook , noted in a 2020 blog post that physics research has drifted away from frequent, persistent physical experimentation to exorbitant infusions of cash into relatively few devices. She writes that with fewer experiments, serendipitous discoveries become increasingly unlikely. Without those discoveries, the technological progress needed to keep experiments economically viable never materializes.

When asked whether this applied equally to warp drive, Hossenfelder sees a faint but plausible connection. “Warp drives are an idea that is not going to lead to applications in the next 1,000 years or so,” she says. “So they don’t play a big role in that one way to another. But when it comes to the funding, you see some overlap in the problems.”

So, despite all the advances, the horizon for a warp drive remains achingly remote. That hasn’t fazed the scientists involved, though. A few years ago, while teaching in France, White visited the Strasbourg Cathedral with his wife. While admiring its 466-foot-tall spire, he was struck by the fact that construction began in 1015 but didn’t wrap up until 1439—a span of 424 years. Those who built the basement had no chance of ever seeing the finished product, but they knew they had to do their part to aid future generations. “I don’t have a crystal ball,” White says. “I don’t know what the future holds. But I know what I need to be doing right now.”

Headshot of Eric Adams

Eric Adams is a writer and photographer who focuses on technology, transportation, science, travel, and other subjects for a wide range of outlets, including Wired, The Drive, Gear Patrol, Men's Health, Popular Science, Forbes, and others.

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Life's Little Mysteries

Can anything travel faster than the speed of light?

Does it matter if it's in a vacuum?

Artist's impression of beams of light

In 1676, by studying the motion of Jupiter's moon Io, Danish astronomer Ole Rømer calculated that light travels at a finite speed. Two years later, building on data gathered by Rømer, Dutch mathematician and scientist Christiaan Huygens became the first person to attempt to determine the actual speed of light, according to the American Museum of Natural History in New York City. Huygens came up with a figure of 131,000 miles per second (211,000 kilometers per second), a number that isn't accurate by today's standards — we now know that the speed of light in the "vacuum" of empty space is about 186,282 miles per second (299,792 km per second) — but his assessment showcased that light travels at an incredible speed.

According to Albert Einstein 's theory of special relativity , light travels so fast that, in a vacuum, nothing in the universe is capable of moving faster. 

"We cannot move through the vacuum of space faster than the speed of light," confirmed Jason Cassibry, an associate professor of aerospace engineering at the Propulsion Research Center, University of Alabama in Huntsville.

Question answered, right? Maybe not. When light is not in a vacuum, does the rule still apply?

Related: How many atoms are in the observable universe?

"Technically, the statement 'nothing can travel faster than the speed of light' isn't quite correct by itself," at least in a non-vacuum setting, Claudia de Rham, a theoretical physicist at Imperial College London, told Live Science in an email. But there are certain caveats to consider, she said. Light exhibits both particle-like and wave-like characteristics, and can therefore be regarded as both a particle (a photon ) and a wave. This is known as wave-particle duality.

If we look at light as a wave, then there are "multiple reasons" why certain waves can travel faster than white (or colorless) light in a medium, de Rham said. One such reason, she said, is that "as light travels through a medium — for instance, glass or water droplets — the different frequencies or colors of light travel at different speeds." The most obvious visual example of this occurs in rainbows, which typically have the long, faster red wavelengths at the top and the short, slower violet wavelengths at the bottom, according to a post by the University of Wisconsin-Madison . 

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When light travels through a vacuum, however, the same is not true. "All light is a type of electromagnetic wave, and they all have the same speed in a vacuum (3 x 10^8 meters per second). This means both radio waves and gamma rays have the same speed," Rhett Allain, a physics professor at Southeastern Louisiana University, told Live Science in an email.

So, according to de Rham, the only thing capable of traveling faster than the speed of light is, somewhat paradoxically, light itself, though only when not in the vacuum of space. Of note, regardless of the medium, light will never exceed its maximum speed of 186,282 miles per second.

Universal look

According to Cassibry, however, there is something else to consider when discussing things moving faster than the speed of light.

"There are parts of the universe that are expanding away from us faster than the speed of light, because space-time is expanding," he said. For example, the Hubble Space Telescope recently spotted 12.9 billion year-old light from a distant star known as Earendel. But, because the universe is expanding at every point, Earendel is moving away from Earth and has been since its formation, so the galaxy is now 28 billion light years away from Earth.

In this case, space-time is expanding, but the material in space-time is still traveling within the bounds of light speed.

Related: Why is space a vacuum?

Diagram of the visible color spectrum

So, it's clear that nothing travels faster than light that we know of, but is there any situation where it might be possible? Einstein's theory of special relativity, and his subsequent theory of general relativity, is "built under the principle that the notions of space and time are relative," de Rham said. But what does this mean? "If someone [were] able to travel faster than light and carry information with them, their notion of time would be twisted as compared to ours," de Rham said. "There could be situations where the future could affect our past, and then the whole structure of reality would stop making sense."

This would indicate that it would probably not be desirable to make a human travel faster than the speed of light. But could it ever be possible? Will there ever be a time when we are capable of creating craft that could propel materials — and ultimately humans — through space at a pace that outstrips light speed? "Theorists have proposed various types of warp bubbles that could enable faster-than-light travel," Cassibry said.

But is de Rham convinced?

"We can imagine being able to communicate at the speed of light with systems outside our solar system ," de Rham said. "But sending actual physical humans at the speed of light is simply impossible, because we cannot accelerate ourselves to such speed.

"Even in a very idealistic situation where we imagine we could keep accelerating ourselves at a constant rate — ignoring how we could even reach a technology that could keep accelerating us continuously — we would never actually reach the speed of light," she added. "We could get close, but never quite reach it."

Related: How long is a galactic year?

This is a point confirmed by Cassibry. "Neglecting relativity, if you were to accelerate with a rate of 1G [Earth gravity], it would take you a year to reach the speed of light. However, you would never really reach that velocity because as you start to approach lightspeed, your mass energy increases, approaching infinite. "One of the few known possible 'cheat codes' for this limitation is to expand and contract spacetime, thereby pulling your destination closer to you. There seems to be no fundamental limit on the rate at which spacetime can expand or contract, meaning we might be able to get around this velocity limit someday."

— What would happen if the speed of light were much lower?

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Allain is similarly confident that going faster than light is far from likely, but, like Cassibry, noted that if humans want to explore distant planets, it may not actually be necessary to reach such speeds. "The only way we could understand going faster than light would be to use some type of wormhole in space," Allain said. "This wouldn't actually make us go faster than light, but instead give us a shortcut to some other location in space."

Cassibry, however, is unsure if wormholes will ever be a realistic option.

"Wormholes are theorized to be possible based on a special solution to Einstein's field equations," he said. "Basically, wormholes, if possible, would give you a shortcut from one destination to another. I have no idea if it's possible to construct one, or how we would even go about doing it." Originally published on Live Science.

Joe Phelan is a journalist based in London. His work has appeared in VICE, National Geographic, World Soccer and The Blizzard, and has been a guest on Times Radio. He is drawn to the weird, wonderful and under examined, as well as anything related to life in the Arctic Circle. He holds a bachelor's degree in journalism from the University of Chester. 

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Why does time change when traveling close to the speed of light? A physicist explains

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Why does time change when traveling close to the speed of light? – Timothy, age 11, Shoreview, Minnesota

Imagine you’re in a car driving across the country watching the landscape. A tree in the distance gets closer to your car, passes right by you, then moves off again in the distance behind you.

Of course, you know that tree isn’t actually getting up and walking toward or away from you. It’s you in the car who’s moving toward the tree. The tree is moving only in comparison, or relative, to you – that’s what we physicists call relativity . If you had a friend standing by the tree, they would see you moving toward them at the same speed that you see them moving toward you.

In his 1632 book “ Dialogue Concerning the Two Chief World Systems ,” the astronomer Galileo Galilei first described the principle of relativity – the idea that the universe should behave the same way at all times, even if two people experience an event differently because one is moving in respect to the other.

If you are in a car and toss a ball up in the air, the physical laws acting on it, such as the force of gravity, should be the same as the ones acting on an observer watching from the side of the road. However, while you see the ball as moving up and back down, someone on the side of the road will see it moving toward or away from them as well as up and down.

Special relativity and the speed of light

Albert Einstein much later proposed the idea of what’s now known as special relativity to explain some confusing observations that didn’t have an intuitive explanation at the time. Einstein used the work of many physicists and astronomers in the late 1800s to put together his theory in 1905, starting with two key ingredients: the principle of relativity and the strange observation that the speed of light is the same for every observer and nothing can move faster. Everyone measuring the speed of light will get the same result, no matter where they are or how fast they are moving.

Let’s say you’re in the car driving at 60 miles per hour and your friend is standing by the tree. When they throw a ball toward you at a speed of what they perceive to be 60 miles per hour, you might logically think that you would observe your friend and the tree moving toward you at 60 miles per hour and the ball moving toward you at 120 miles per hour. While that’s really close to the correct value, it’s actually slightly wrong.

This discrepancy between what you might expect by adding the two numbers and the true answer grows as one or both of you move closer to the speed of light. If you were traveling in a rocket moving at 75% of the speed of light and your friend throws the ball at the same speed, you would not see the ball moving toward you at 150% of the speed of light. This is because nothing can move faster than light – the ball would still appear to be moving toward you at less than the speed of light. While this all may seem very strange, there is lots of experimental evidence to back up these observations.

Time dilation and the twin paradox

Speed is not the only factor that changes relative to who is making the observation. Another consequence of relativity is the concept of time dilation , whereby people measure different amounts of time passing depending on how fast they move relative to one another.

Each person experiences time normally relative to themselves. But the person moving faster experiences less time passing for them than the person moving slower. It’s only when they reconnect and compare their watches that they realize that one watch says less time has passed while the other says more.

This leads to one of the strangest results of relativity – the twin paradox , which says that if one of a pair of twins makes a trip into space on a high-speed rocket, they will return to Earth to find their twin has aged faster than they have. It’s important to note that time behaves “normally” as perceived by each twin (exactly as you are experiencing time now), even if their measurements disagree.

You might be wondering: If each twin sees themselves as stationary and the other as moving toward them, wouldn’t they each measure the other as aging faster? The answer is no, because they can’t both be older relative to the other twin.

The twin on the spaceship is not only moving at a particular speed where the frame of references stay the same but also accelerating compared with the twin on Earth. Unlike speeds that are relative to the observer, accelerations are absolute. If you step on a scale, the weight you are measuring is actually your acceleration due to gravity. This measurement stays the same regardless of the speed at which the Earth is moving through the solar system, or the solar system is moving through the galaxy or the galaxy through the universe.

Neither twin experiences any strangeness with their watches as one moves closer to the speed of light – they both experience time as normally as you or I do. It’s only when they meet up and compare their observations that they will see a difference – one that is perfectly defined by the mathematics of relativity.

Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to [email protected] . Please tell us your name, age and the city where you live.

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Star Trek: What Is Warp Speed?

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Best accessories for star trek fans, 10 best star trek games of all time, quick links, what is warp speed, how fast is warp speed, does warp speed make distance meaningless, what is warp 10, is warp travel safe, is warp speed actually possible.

One of the most famous features of the Star Trek setting is Warp speed, one of those rare notions that passes over from a single series into pop culture and the public consciousness at large. It may be one of the most well-known aspects of Star Trek overall.

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One thing Star Trek doesn't do very much of is explain the technology depicted on the show, largely because almost all of it is fictional. But the question remains, what is Warp speed, both in the setting and scientifically? We're here to lay it all out for you.

We will be using terms to help describe what Warp is and how it functions that would need their own articles or academic papers to explain, so the focus will be on exploring the idea of Warp specifically and not the surrounding concepts.

The actual name is Time-Warp Factor, shortened to Warp Factor, usually shortened even further down to just Warp. It is a form of faster-than-light travel , allowing the interstellar travel that Star Trek is so famous for.

Without travel at the speeds that Warp allows, travel from one star system to another would take years at a minimum . It's why other sci-fi shows or movies without Warp show characters needing to be put into stasis during travel, they would otherwise lose years of their life getting from one place to another.

For an example of great sci-fi that uses stasis or cryosleep to keep a ship's crew or passengers alive during long stretches of travel you can look to the likes of Alien, Lost In Space, or even Star Trek itself .

Although this would mean you reached a distant destination without aging, time would still progress while you were asleep . For you, it would be a short nap, but for everyone else years could have passed by. It's almost a form of time travel, but a major drawback to the method.

Other examples of sci-fi, like Stargate, use the idea of wormholes for long-distance travel, a shortcut from one part of space to another. Star Trek also features wormholes, most notably in Deep Space Nine, but Warp is still the most common method used to traverse long distances.

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According to Star Trek, it worked by creating a subspace bubble around the ship, which distorted the spacetime continuum and moved the ship at extreme velocities that wouldn't otherwise be possible.

In both mathematics and physics, the spacetime continuum is the singular continuum in which three-dimensional space and time co-exist. To break that down, this means Warp speed is altering the laws of physics to achieve extreme speed.

Warp technology was the deciding factor in a civilization joining the interstellar community — without it they wouldn't be able to engage in trade, exploration, or diplomacy to any reasonable standard . The United Federation of Planets would even specifically avoid pre-Warp civilizations to avoid influencing their development.

A ship losing Warp speed, by damage or malfunction, would often be left close to stranded. The alternative was Impulse, not dissimilar to conventional propulsion , reducing a ship's speed dramatically. Ships in this situation would typically need to send out a distress call for help.

Not all of the seemingly scientific language featured in Star Trek really means anything. Some concepts are rooted in real science, but since Star Trek is fiction the writers are free to invent any technology or concept that best serves the story.

If you've ever watched a scene where the engineer or scientist has to deliver a string of scientific-sounding words to make the topic sound real, it's usually nonsense. This spawned the term Treknobabble , a twist on the word technobabble. LeVar Burton, who played Jordi La Forge, found the best way to deliver these lines was as quickly as possible.

Warp speed has different levels, ranging most typically from Warp 1 up to Warp 9 . There are increments in between, like Warp 2.5 in between Warp 2 and Warp 3. The series doesn't offer too much explanation about how fast these speeds are, but there is concrete information.

Warp 1 is equivalent to the speed of light, approximately 186,000 miles per second. That's 671 million miles per hour , which sounds impossibly fast. But even to get from Earth to Alpha Centauri, our nearest neighboring star system, would take over four years at light speed.

Star Trek creator, Gene Roddenberry, initially pictured ships moving at Warp speed as invisible. He believed that since they were moving faster than the speed of light, light wouldn't reach them. Science doesn't support that idea , but more importantly, it wouldn't be as visually interesting for viewers.

Warp 2, the next full factor of speed up from Warp 1, is about eight times as fast as Warp 1, which cuts down the time to reach Alpha Centauri to less than a year. Warp 3 is 27 times faster than Warp 1, and it continues to escalate from there. The higher Warp speeds can be thousands of times faster than the speed of light .

You can see how speeds at that level make space travel across long distances a matter of days rather than centuries, allowing Star Trek to explore multiple star systems and planets. Otherwise, most of the action would be constrained to a much smaller section of the galaxy .

It would be easy to think that Warp means travel is a non-factor in Star Trek, but that isn't the case. The universe is so infinitely vast that travel across long distances, even at top Warp speeds, can take months if not longer .

The best example of this is Star Trek Voyager, a show that explores the idea of a Starfleet ship stranded in a far-flung and unexplored corner of the universe. They calculate that even if they traveled at top Warp speed, non-stop, it would still take them around 75 years to get home .

The Voyager crew managed this journey in just seven years, utilizing advanced technology and a number of shortcuts . Their efforts to find a way home caused several advances in interstellar travel, including Warp 10.

Warp 10 is treated differently depending on which Star Trek series you happen to be watching. In the original and animated series , Warp speeds of up to 36 are depicted, but Star Trek would go on to reclassify top speeds.

By the 24th century, they had classed Warp 10 as the point at which infinite velocity was reached , causing the ship to exist everywhere in the universe at once. It was also known as the transwarp threshold and considered impossible to reach.

Warp 10 also became slang for anything that moved extremely fast, a hyperbolic phrase. In Star Trek Voyager, rumours are described as travelling at Warp 10, while in Deep Space Nine a character's adrenaline is said to be pumping at Warp 10 at one point.

Warp 10 is achieved a few times in Star Trek, most notably in Star Trek Voyager as a possible way to get the crew home faster. It was achieved by fitting a shuttlecraft with a transwarp drive and using a rare form of dilithium.

Although the test flight was successful, it was discovered that traveling at Warp 10 caused hyper-evolution , meaning they would undergo millions of years of evolution in a matter of hours. Tom Paris, along with Captain Janeway, underwent this process.

They both evolved into amphibious salamanders, not that it's clear how that is constituted as an evolution. They would have several offspring in this form before the process was successfully reversed. Unsurprisingly, it was decided Warp 10 wasn't worth the risks .

Star Trek is no stranger to time travel, showing possible alternatives to faster speeds in the future. Some possible future technologies shown include the quantum slipstream drive or the Sidewarp Factor. Sidewarp, featured in one of the official Star Trek novels , Federation, is described as so fast that regular Warp feels like moving at a crawl in comparison.

The offspring Tom Paris and Captain Janeway have while hyper-evolved are left to fend for themselves on the planet they were born on. Their ultimate fate is unknown .

Warp travel is the primary method of travel for almost all interstellar species in the Star Trek universe, and has no true viable replacement. Given how it's how almost all travel is carried out, the question arises of whether it's safe or not.

In the year 2370, it was discovered that Warp engines were damaging the fabric of spacetime , causing subspace rifts. Captain Picard compared it to how walking over a carpet repeatedly will eventually cause enough gradual damage to wear it down.

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The temporary solution to this was for Starfleet to impose a speed limit of Warp 5 outside of emergencies , to try and reduce the damage caused to subspace. It was believed that lower speeds would cause less damage.

Starfleet imposed this speed limit and communicated the issue to other civilizations, but there was never any guarantee they would be as environmentally conscious. Rival groups like the Cardassians or Romulans would have huge advantages over Starfleet by not adhering to the same speed limit.

This speed limit was mentioned only a few further times and then quietly dropped. It's possible that a solution was found to the problem, but the truth is that the writers for Star Trek just quietly did away with the idea . Although it was interesting, the issues it caused weren't worth it for the sake of writing interesting stories.

Every Star Trek fan has wondered at some point or another whether Warp travel is something we could achieve , allowing us to travel to the stars at the kind of speeds depicted in the various Star Trek shows and movies.

There isn't a simple or definitive answer to this question. We certainly don't have the ability to move at anything even remotely approaching Warp speed yet, many scientists are firm in the idea that nothing with mass could move at the speed of light, let alone faster.

It's important to remember that even in the fictional setting of Star Trek, faster than light travel isn't possible most of the time. Warp speed achieves this by creating a shell around a ship, which means that space and time no longer function under their normal rules.

Still, Warp could be possible if you listen to some scientists, at least in theory if not in practice. As recently as 2024, applied physics researchers suggested the idea of a "constant-velocity subluminal warp drive" that accords with the principles of relativity.

What that means exactly requires advanced scientific degrees and a lot of time to explain, but it's enough to know that the idea is still alive . We can still hope and dream of someday hitting Warp speeds and flying through space faster than light after dramatically saying... Engage.

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A Missy Elliott Song Travels to Venus at the Speed of Light

NASA sent the song “The Rain (Supa Dupa Fly)” from a radio dish in California last week. It took 14 minutes to travel the 158 million miles.

A woman, wearing a white shirt with colorful decorations, holds a microphone onstage.

By Mike Ives

Missy Elliott has broken lots of boundaries, but until recently they were all Earth-based.

Last week, giant radio towers transmitted her song “The Rain (Supa Dupa Fly)” to Venus for the benefit of whatever life-forms might have been around , or not, to listen.

The July 12 transmission, announced by NASA on Monday, was made at the speed of light by a 112-foot-wide radio dish near Barstow, Calif. It took the song 14 minutes to travel 158 million miles to Venus, Elliott’s favorite planet.

“My song ‘The Rain’ has officially been transmitted all the way to Venus, the planet that symbolizes strength, beauty and empowerment,” she wrote on social media . “The sky is not the limit, it’s just the beginning.”

As Elliott bantered with social media users on Monday, she uploaded pictures of planets, GIFs of dancing aliens and videos from her latest tour, “Out of This World.”

“The Rain” was transmitted to Venus through the Deep Space Network , a NASA system that helps the agency communicate with its far-flung spacecraft. In addition to the site in California, the network has some in Australia and Spain, each 120 degrees longitude apart. That way spacecraft can stay in touch even as the planet rotates.

In 1969, the network’s antennas heard from the astronaut Neil Armstrong as he planted his feet on the moon’s surface.

“That’s one small step for man, one giant leap for mankind,” Armstrong said after stepping off the ladder of a landing craft. (There has been some debate over whether he said “man” or an indistinct “a man.”)

But “The Rain” is only the second song that the network has sent into space. The first, “Across the Universe" by the Beatles, was beamed to the North Star, Polaris, in 2008.

“Send my love to the aliens,” Paul McCartney, one of the two remaining Beatles, said at the time .

The North Star sits hundreds of light years away from Earth. In comparison, Venus, the second planet from the Sun, is right around the corner .

It’s also the only planet whose namesake is a female god. In ancient Rome, Venus was the goddess of love and beauty. The ancient Greeks knew her as Aphrodite.

The collaboration was NASA’s idea, the agency said in its statement.

“Both space exploration and Missy Elliott’s art have been about pushing boundaries,” Brittany Brown, NASA’s director of digital communications, said in the statement, which highlighted her use of space themes and futuristic visuals in music videos.

NASA did not say when the collaboration was proposed or whether other songs or artists were considered. A representative for Elliott, who last year became the first female hip-hop artist inducted into the Rock & Roll Hall of Fame , could not be reached for comment overnight.

NASA has been playing music to astronauts for decades. In 1965, astronauts aboard an earth-orbiting spacecraft heard Jack Jones singing a parody of the Broadway hit “Hello, Dolly!”

In a similar vein, the actor Robin Williams sang a parody of the theme song for the television show “Green Acres” to the crew of the Space Shuttle Discovery in 1988.

“Here’s a little song coming from the billions of us to the five of you,” he told them.

Glen Nagle, a spokesman at the Deep Space Network’s site in Canberra, Australia, said in an email on Tuesday that NASA’s collaboration with Elliott was part of that tradition, and a key to engaging a new generation of “scientists, explorers and dreamers.”

“Artists such as Missy Elliott and the Beatles have had their music beamed into space to inspire humanity to think about Earth’s place in the cosmos — and maybe others, if they’re out there to hear it,” he said.

Mike Ives is a reporter for The Times based in Seoul, covering breaking news around the world. More about Mike Ives

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Is Pluto a planet? And what is a planet, anyway? Test your knowledge here .

how many nanoseconds does it take light to travel 1.0 km in a vacuum? the speed of light is 2.99 x 108 m/s

The speed of light is 3344 nanoseconds per second.

186 thousand miles per second

Fast is light! The maximum speed it can go is 186,000 per second. (The cosmos would appear radically different if one could move at the speed of light.) Light flows so swiftly that it might appear to appear instantly.

Nothing can go faster than 300,000 kph. Only massless particles, like the photons that make up light, are able to move so quickly. Any material item cannot be accelerated to the rate of light since doing so would need a limitless supply of energy .

The speed of light , c = 2.99 * [tex]10^{8}[/tex] m/s

distance d= 1km

d= [tex]10^{3} m[/tex]

the amount of time light needs to reach this distance

[tex]t=\frac{d}{c} \\[/tex]

[tex]=\frac{10^{3} }{2.99*10^{8} }[/tex]

[tex]t=0.3344*10^{-5}s[/tex]

[tex]t=3.344*10^{-6}s[/tex]

One nanosecond =[tex]10^{-9} s[/tex]

Therefore [tex]3.344*10^{-6} s[/tex]

[tex]t=3.344*10^{-6}*10^{9}[/tex] nanosecond

[tex]=3.344*10^{3}[/tex]

[tex]t= 3344[/tex] nanosecond

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Related Questions

a boat capable of moving at 4.00 m/s needs to travel straight across a 20.0-meter-wide river that is moving at 2.00 m/s. that is, the boat can't end up downstream. at what angle, relative to the direction straight across the river, must the boat point in order to make it straight across?

At 26.56° relative to the direction straight across the river, must the boat point in order to make it straight across.

Upstream - A boat is said to be moving upstream if it is moving downstream of the stream. The term "upstream speed" in this context refers to the boat's net speed.

Downstream - A boat is said to be moving downstream if it is moving in the same direction as the stream.

The Pythagorean theorem can be used to determine the final velocity . The outcome is a right triangle with sides of 4 and 2 metres, and that triangle's hypotenuse. It is,

√[ (4 m/s)2 + (2 m/s)2 ] = 4.47 m/s

Its direction can be determined using a trigonometric function.

Direction = tan⁻¹ [ (2 m/s) / (4 m/s) ] = 26.56°

Therefore, at 26.56° relative to the direction straight across the river, must the boat point in order to make it straight across.

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a thin converging lens is found to form an image of a distant building 38 cm from the lens. if an insect is now placed 12 cm from this lens, how far from the insect will its image be formed?

The image of the distant building is formed 38 cm from the lens . When an insect is placed 12 cm from the lens , the image of the insect will be formed at a different distance .

To calculate this distance , the thin lens equation must be used. The thin lens equation is

1/f = 1/[tex]d{1}[/tex] + 1/[tex]d_{2}[/tex],

where f is the focal length of the lens,

[tex]d{0}[/tex] is the object distance, and [tex]d{i}[/tex] is the image distance. In this case, the object distance is 12 cm, so the image distance is determined by solving the equation

1/f = 1/12 + 1/[tex]d{i}[/tex], which yields

[tex]d_{i}[/tex] = -24 cm.

This means the image of the insect will be formed 24 cm from the insect, as the negative sign indicates the image is on the opposite side of the lens from the insect.

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what is the minimum value of the coefficient of static friction that will keep the snow from sliding down?

The snow chunk will not slide down unless the static coefficient of friction is at least 0.70.

The roof slopes down at an angle of = 35° from horizontal.

The smallest static friction coefficient required to stop the snow chunk from slipping is,

μs = tan (35)

The ratio of the greatest static friction force (F) between the surfaces in contact before movement starts to the normal force (N) is known as the coefficient of static friction.

When mechanical interactions are removed, friction coefficients as low as 0.05 between dry sliding surfaces have been attained. This outcome was attained using a fictitious model of the ideal surface for minimal friction.

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The given question is incomplete. The complete question is:

Piles of snow on slippery roofs can become dangerous projectiles as they melt. Consider a chunk of snow at the ridge of a roof with a slope of 35 degrees.

What is the minimum value of the coefficient of static friction that will keep the snow from sliding down? Express your answer using two significant figures.

Where were the bodies of Columbia found?

The bodies of Columbia found in Lake Nacogdoches and the Toledo Bend Reservoir.

All of the astronauts ' remains were recovered in East Texas . “Every time remains were recovered, they would pause and everything and have a moment of silence,” said Orwig . Two decades later, pieces of the shuttle are still being found, a reminder of this tragic historical event that took place in the Texas sky.

The remains of all seven astronauts were recovered, despite the obstacles of terrain and the scope of the search. Searchers combed through pine forests, hundreds of thousands of acres of underbrush, and boggy areas. Parts of the shuttle were found in Lake Nacogdoches and the Toledo Bend Reservoir .

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what is the unit of electric field? group of answer choices field is just a direction, it does not have units nm n/m n/c

Unit of electric field is V/m,where V is Volt and m is meter.Electric field is a vector quantity.

An electric field is the actual field that encompasses electrically charged particles and applies force on any remaining charged particles in the field, either drawing in or repulsing them. It likewise alludes to the actual field for an arrangement of charged particles. Electric fields start from electric charges and time-fluctuating electric flows. Electric fields and attractive fields are the two appearances of the electromagnetic field, one of the four principal communications (likewise called powers) of nature.

The electric field is characterized as a vector field that partners to each point in space the electrostatic (Coulomb) force per unit of charge applied on a tiny positive test charge very still at that point. The determined SI unit for the electric field is the volt per meter (V/m), which is equivalent to the newton per coulomb.

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let the photon source be a helium-neon laser with a wavelength of 632.8 nm and a power of 1 mw. if each filter transmits only 5% of the power incident on it, how many filters are required in our experiment?

If each filter transmits only 5% of the power incident on it, 20 filters are required in our experiment .

Let's call the number of filters required "n".

The power of the laser is 1 mW and each filter transmits only 5% of the power,

The power transmitted by each filter is

= 0.05 x 1 mW

= 1 mW ÷ 0.05 mW

= 20 filters

we need to understand the concept of power transmission through filters. The power transmitted through a filter depends on the fraction of the incident light that is transmitted. The fraction of the incident light that is transmitted is known as the transmittance of the filter. In this case, the transmittance of each filter is 5%, which means that only 5% of the incident light is transmitted through each filter. The rest of the light is absorbed or scattered by the filter.

Hence, This means that 20 filters are needed in the experiment to reduce the power of the laser to the desired level.

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Which material is likely to experience a nearly elastic collision? Write a paragraph of at least 6 sentences. Be sure to use evidence from the experiment to support your explanation.

Billiard balls, ping-pong balls and other hard substances have nearly elastic collision.

An example of an elastic collision is when two balls collide at a pool table . It is an elastic collision when you throw a ball at the ground and it bounces back to your hand because there is no net change in the kinetic energy.When two objects collide in an elastic collision, they disperse after impact and retain all of their kinetic energy . The energy of motion, or kinetic energy, is discussed in more depth elsewhere. When the net external force on a system is zero, the law of conservation of momentum can be used, which is highly helpful in this situation.

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If the diameter of Mara is 53.3 percent of Earths diameter (12,756km), determine its diameter in kilometers

The diameter of mars in kilometers is 6,799 km

Any straight line segment that traverses a circle's center and has endpoints that are on the circle is considered a segment of the circle's diameter . The circle's longest chord is another way to describe it. For a sphere's diameter, both definitions are appropriate.

As you are aware: 12,756 km is Earth's diameter; the percentage of Earth's diameter: 53.3% in decimal form is 0.533 (53.3% 100).

You must look for the following: the size of Mars

The equation you must apply is as follows: (Earth's radius) (decimal equivalent)

the size of Mars

Find the solution to the equation for Mars' diameter: (12,756 km) (0.533) (0.533)

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The complete question is-The diameter of the Earth is 12,756 kilometers. Mars has a diameter that is 53.3 percent that of Earth. Determine the diameter of Mars.

would a plucked guitar string vibrate for a longer time or a shorter time if the instrument had no sounding board? why?

A plucked guitar string would vibrate for a shorter time if the instrument had no sounding board. A sounding board, also known as a soundboard, is a large, flat surface on the top of a guitar that amplifies the sound produced by the strings. The soundboard provides a large surface area for the vibration of the strings to be transferred to, increasing the volume of the sound and the length of time that the strings vibrate.

Without a sounding board, the strings of a guitar would vibrate more weakly and for a shorter amount of time. The energy produced by the strings would not be effectively transferred to the surrounding air, leading to a decrease in volume and a decrease in the duration of the vibration.

In summary, the sounding board plays an important role in amplifying the sound of a guitar and maintaining the vibration of the strings for a longer period of time. Without it, the strings would vibrate for a shorter time and produce a weaker, less vibrant sound.

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the plate is moving at 0.6 mm/s when the force applied to the plate is 4 mn. if the surface area of the plate in contact with the liquid is 0.5 m2, determine the approximate viscosity of the liquid, assuming that the velocity distribution is linear.

The approximate viscosity of the liquid is undefined .

To determine the viscosity of a liquid, we can use the equation for the shear force:

F = η * A * (du/dy)

where F is the force applied to the plate, η is the viscosity of the liquid, A is the surface area of the plate in contact with the liquid, and (du/dy) is the velocity gradient in the liquid.

Given that F = 4 mN and A = 0.5 m^2, we can find the velocity gradient (du/dy) as follows:

du/dy = F / (η * A)

=> [tex]\frac {4 \times 10^{-3} N } {n \times 0.5 m^2}[/tex]

Next, we can use the linear velocity distribution, which states that the velocity of the liquid is proportional to the distance from the plate. If we let the velocity of the liquid at the plate be u and the velocity at the top of the liquid be 0, we have:

u = (du/dy) * y

At the plate, y = 0 and u = 0.6 mm/s, so we can substitute these values into the equation above:

0.6 * 10^(-3) m/s = (du/dy) * 0

du/dy = 0.6 * 10^(-3) m/s / 0

=> undefined

The equation cannot be used in this case, since the velocity gradient is undefined at the plate. This indicates that the linear velocity distribution assumption is not valid in this situation and a different approach is needed to determine the viscosity of the liquid.

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a cannonball is launched horizontally off a 70 m high castle wall with a speed of 70 m/s. how long will the cannonball be in the air before striking the ground?

The cannonball will be in flight for 3.7 seconds in the air before striking the ground.

The position vector of the cannonball at a time t is conveyed by the following equation:

r = x₀ + v₀ • t, y₀ + 1/2 • g • t²

r = position vector of the cannonball at time t.

x₀ = initial horizontal position

v₀ = initial horizontal velocity

y₀ = initial vertical position

g = acceleration due to gravity (-9.8m/s² considering the upward direction as positive).

Let's site the origin of the frame of reference on the ground, at the rim of the wall so that the initial position vector is r₀ = (0,70)m.

Operating the equation of the vertical component of the position vector r, we can see the time it takes the ball to get to the ground:

y = y₀ + 1/2 • g • t²

When the cannonball arrives on the ground, y = 0:

0 = 70m - 1/2 • 9.8 m/s² • t²

-70m / -4.9 m/s² = t²

Therefore, the cannonball will be in flight for 3.7 seconds in the air before striking the ground.

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a device that produces electricity by transforming chemical energy into electrical energy is called a

A battery is a device that stores chemical energy and converts it into electrical energy. A chemical reaction within a battery involves the flow of electrons from one material (the electrodes) to another through an external circuit .

A battery is a device that converts chemical energy contained in active materials directly into electrical energy through an electrochemical oxidation-reduction (redox) reaction. In this type of reaction, electrons are transferred from one substance to another through an electrical circuit . Historically, the word " battery " was used to describe "a series of similar objects grouped together to perform a function", like a cannon battery. Benjamin Franklin first used the term in 1749 to describe a series of capacitors he connected for his electrical experiments.  

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How do the alkali metals compare to the alkaline earth metals with respect to reactivity?

It takes more energy to remove two valence electrons from an atom than one valence electron . This makes alkaline Earth metals with their two valence electrons less reactive than alkali metals with their one valence electron.

Alkali metals, which make up all of the group 1 elements, are soft in composition. Alkali earth metals make up all of the group two elements, and they are all hard in composition. Low melting points describe them. Compared to alkali metals, alkali earth metals have a higher melting point.

The valence of all alkali metals is 1, but that of alkaline earth metals is 2. They create ionic compounds with non-metals because they are metals. Alkali metals in these compounds have a 1+ charge (like NaCl), whereas alkaline earth metals have a 2+ charge (such as in MgCl2).

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what is the internal resistance of a 12.0- v car battery whose terminal voltage drops to 8.4 v when the starter motor draws 78 a ?

The internal resistance of a 12V car battery is calculated using Ohm's Law, which states that the voltage (V) is equal to the current (I) times the resistance (R).

Internal resistance is the resistance to the flow of current within a device, such as a battery or resistor. It is measured in ohms (Ω) . In electrical circuits, a certain amount of internal resistance is always present due to the nature of the components and the connections between them. Internal resistance has a significant effect on the operation of the circuit, affecting the amount of current that can flow through it, the power output, and the voltage drop.

In this case, the voltage (V) is 12V, and the current (I) is 78A. Therefore, the internal resistance (R) is equal to V/I, or 12V/78A, which is equal to 0.154 ohms.This means that when the starter motor draws 78A , the voltage across the terminals of the battery drops from 12V to 8.4V. This drop in voltage is caused by the internal resistance of the battery, which is 0.154 ohms. To learn more about   internal resistance https://brainly.com/question/29526419 #SPJ4

a rolling ball moves from to during the time from to what is its average velocity over this time interval?

The displacement is the straight-line distance between the starting and ending positions if the ball travels along a curved path.

It is impossible to give a numerical answer without particular values for the distance travelled and the amount of time that has passed. The displacement of the ball divided by the time interval, however, yields the average speed of the rolling ball over a period of time. Between the beginning and final points, the ball's position changes, and this is known as displacement. The displacemen t is only the difference between the ball's final and initial positions if it goes in a straight path. The displacement is the straight-line distance between the starting and ending positions if the ball travels along a curved path.

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Which method of measurement is most likely to be both accurate and precise? A. Measuring the temperature of a pond using a digital thermometer OB. Measuring the temperature difference between two objects by comparing how they feel C. Measuring the speed of a runner by comparing it to that of other runners O D. Measuring time using a clock that has slowed down

The method of measurement most likely to be both accurate and precise is measuring the temperature of a pond using a digital thermometer , as listed in Option A, as there is less chance of mistakes when measured by machines .

Accuracy refers to how close the measured value is to the true value, while precision refers to how reproducible the measurements are, and using digital thermometers is typically accurate and precise because there is a lower chance of human-like mistakes.

Hence, the method of measurement most likely to be both accurate and precise is measuring the temperature of a pond using a digital thermometer , as listed in Option A.

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raise his hand up far enough not to produce a spark. give him 5 or so kicks to move some electrons and then let go. which way do the electrons drift within john? why?

It is not accurate to assume that electrons within a human body drift in  particular direction or that a spark will result from raising a hand. The movement of electrons within the human body is a complex process that is influenced by a variety of factors, including chemical reactions, electric fields , and ionic gradients.

The movement of electrons is regulated by complex biological processes, and it is not possible to determine the direction of electrons giving a kick.

Electrical properties of human body are not well understood, it is unsafe to assume that spark will result from a specific action.

It is important to respect the electrical safety and avoid getting exposed to electrical currents that can cause injury.

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if the electric field at (just barely outside) the surface of the sphere is 750 kn/c and points outward, what is the charge of the point charge? expre

Complete Question: 4.8 mu C is carried by a 15 cm in diameter thin, spherical shell that is evenly dispersed over its surface. Towards the shell's core, there is a point charge. What is the charge of the point charge if the electric field is 750 kN/C and points outward at the sphere's surface? Your response should include two significant figures.

Charge of the point charge that produces the observed electric field just outside the surface of the spherical shell is [tex]2.81 * 10^-7[/tex]Coulombs.

The electric field at a point just outside the surface of a thin spherical shell is equal to the electric field produced by a point charge located at the center of the shell. Therefore, we can assume that the electric field just outside the surface of the shell is due to a point charge Q located at the center of the sphere.

The electric field produced by a point charge at a distance r from the charge is given by the equation E = [tex]kQ/r^2[/tex], where k is Coulomb's constant (approximately [tex]9 * 10^9 Nm^2/C^2[/tex]). The electric field just outside the surface of the spherical shell is given as 750 kN/C, which is [tex]7.5 * 10^5 N/C.[/tex]

The radius of the spherical shell is 15 cm, or 0.15 m. The charge on the spherical shell is given as 4.8 microCoulombs, or [tex]4.8 * 10^-6[/tex] Coulombs. We can use the equation for electric field produced by a point charge to find the charge Q at the center of the shell that produces the observed electric field just outside the surface:

E = [tex]kQ/r^2\\[/tex]

Q = [tex]Er^2/k[/tex] = [tex](7.5 * 10^5 N/C) * (0.15 m)^2 / (9 * 10^9 Nm^2/C^2)[/tex]= [tex]2.81 * 10^-7 C[/tex]

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given (us is spring potential energy ; x is spring extension). how do you find the value of k from a graph?

The value of the spring constant (k) can be determined from a graph of spring potential energy (U) versus spring extension (x).

The relationship between spring potential energy and spring extension is given by the formula:

U = 1/2 * k * x^2

where U is the s pring potential energy , k is the spring constant, and x is the spring extension.

To find the value of k from a graph, you need to make a plot of U versus x and determine the slope of the graph. The slope of the graph is proportional to k. To get the exact value of k, you need to use the formula for spring potential energy and solve for k.

For example, if you have two points on the graph, (x1, U1) and (x2, U2), you can use the formula for spring potential energy to find the value of k:

U1 = 1/2 * k * x1^2

U2 = 1/2 * k * x2^2

Dividing the two equations and solving for k, we get:

k = 2 * (U2 - U1) / (x2^2 - x1^2)

Once we have found the value of k, we can use the formula for spring potential energy to calculate the spring potential energy for any given extension.

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Which two statements describe reasons that semiconductors must be included in a solar cell? A. They form a zone of separation between the glass layer and the terminal layer. B. They provide a path through which released electrons move to form an electric current. c. They provide a path through which electrons exit the surface of the cell and never return. D. They provide a source of electrons to be released by the photoelectric effect.

The following two reasons are why semiconductors must be present in a solar cell:

A. Semiconductors provide an avenue for the electrons that the photoelectric effect releases.

C. Semiconductors provide the electrons needed to create an electrical current.

When a substance absorbs electromagnetic radiation , a process known as the photoelectric effect causes electrically charged particles to be discharged from or inside the material.

When a transistor is confronted with light, it absorbs the electricity and transmits it to the substance. This causes energy to reach the negatively charged electron , allowing the particle to flow as an electric current through the substance.

Consequently, the answer is A. Semiconductors provide a route for the electrons which are emitted as a result of the photoelectric effect.

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The two statements that describe reasons why semiconductors must be included in a solar cell are:

B. They provide a path through which released electrons move to form an electric current.

D. They provide a source of electrons to be released by the photoelectric effect.

Semiconductors play a crucial role in solar cells. When sunlight strikes the semiconductor material, it excites electrons, allowing them to be released and flow as an electric current. This process is known as the photoelectric effect. The semiconductor acts as a pathway for these released electrons, allowing them to move and create an electric current. Therefore, options B and D accurately describe the roles of semiconductors in a solar cell.

a spring of spring constant 19.6 n/m is compressed 5.00 cm. a mass of 0.300 kg is attached to the spring and released from rest. what is the period of oscillation?

A spring of spring constant 19.6 n/m is compressed 5.00 cm. a mass of 0.300 kg is attached to the spring and released from rest then the period of oscillation is 0.691 seconds.

The period of oscillation of a mass-spring system can be calculated using the formula: T = 2π √(m/k) where T is the period of oscillation , m is the mass attached to the spring, and k is the spring constant.

In this problem, the spring constant is given as 19.6 N/m, and the mass attached to the spring is 0.300 kg. To calculate the period , we first need to find the effective spring constant of the system.

When the spring is compressed by 5.00 cm, it exerts a force on the mass given by:

where x is the displacement of the spring from its equilibrium position. In this case, x = 0.050 m, so the force exerted by the spring is:

F = (19.6 N/m) x (0.050 m) = 0.98 N

This is also the weight of the mass, since it is released from rest. Therefore, the effective spring constant of the system is:

k' = F/x = 0.98 N / 0.050 m = 19.6 N/m

which is the same as the original spring constant.

Now we can use the formula for the period of oscillation:

T = 2π √(m/k')

Substituting the given values, we get:

T = 2π √(0.300 kg / 19.6 N/m) = 0.691 s

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What is the wavelength of a sound wave that has a frequency of 220hz

Ryan enters the highway at a speed of 24 m/s. He steps on his accelerator for 14 seconds, speeding up with an acceleration of 1.2 m/s2. What is his distance traveled during this time?

The distance traveled by Ryan during this time is 453.6 m.

The distance traveled by Ryan is calculated as follows;

s = vt   + ¹/₂at²

The distance traveled by Ryan during this time ( t = 14 seconds ) is calculated as follows;

s = ( 24 m/s x 14 s ) +   ¹/₂ (1.2 m/s² ) ( 14 s )²

s = 453.6 m

Thus, the distance traveled by Ryan is a function of the acceleration and time of motion.

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If a force of 2N is applied on a surface with area of 4sq. M,then find the pressure exerted on that surface?

Pressure is defined as the force per unit area and can be calculated as:0.5 Pa (pascals)

As per the data given in the above question are as bellow,

The provided data are as bellow,

F = 2 N (applied force)

A = 4 m^2 ( surface area )

So, the pressure exerted on the surface can be calculated as:

p = 2 N / 4 m^2

= 0.5 N/m^2

= 0.5 Pa (pascals)

The force delivered perpendicularly to an object's surface per unit area across which that force is dispersed is known as pressure. In comparison to the surrounding pressure, gauge pressure is the pressure. The units used to indicate pressure vary.

The standard unit of pressure is a pascal (Pa). Given that a pascal is a relatively small unit of pressure, the kilopascal is the most appropriate measurement for commonplace gas pressures (kPa). 1000 pascals make up one kilopascal. The atmosphere is another frequently used measurement of pressure (atm)

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. a river has a steady speed of 0.30 m/s. a student swims downstream a distance of 1.2 km and then swims back to the starting point. if the student swims with respect to the water at a constant speed and the downstream portion of the swim requires 20 minutes, how much time is required to swim back to the original starting point from downstream destination?

The swimmer's speed with respect to the water v. The downstream velocity of the swimmer is given by the sum of the river velocity and the swimmer's velocity 33.33 minutes

v_downstream = 0.30 m/s + v

The time required to swim 1.2 km downstream is 20 minutes, or

20 * 60 = 1200 seconds.

So the downstream velocity can be found as:

v_downstream = d / t = 1.2 km / (1200 s)

= 0.001 m/s

Rearranging the above equation , we get the swimmer's velocity:

v = v_downstream - 0.30 m/s

= 0.001 m/s - 0.30 m/s

= -0.299 m/s

The upstream velocity of the swimmer is given by the difference of the river velocity and the swimmer's velocity:

v_upstream = 0.30 m/s - v

= 0.30 m/s - (-0.299 m/s)

= 0.599 m/s

The time required to swim back to the original starting point from the downstream destination is the same as the time required to swim 1.2 km upstream:

t = d / v_upstream = 1.2 km / (0.599 m/s)

= 2.00 s * 10^3 s

= 33.33 minutes

So it would take 33.33 minutes to swim back to the original starting point from the downstream destination.

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a toy dart with a mass of 0.013 kg is fired from a spring-loaded dart gun in the horizontal direction. the spring inside the gun has an elastic constant of 33 n/m and the spring is compressed a distance of 0.03 m inside the gun when the dart is loaded. what will be the speed of the dart when it leaves the gun?

The velocity of the dart when it leaves the gun will be approximately 318.38 m/s.

Velocity is a physical quantity that represents the rate of change of an object's position with respect to time. It is a vector quantity, meaning it has both magnitude and direction. The magnitude of velocity is commonly referred to as speed, while the direction represents the object's motion.Velocity is defined as the derivative of an object's position with respect to time.

It is related to other physical quantities, such as acceleration and force . For example, a change in velocity, or acceleration, is produced by a net force acting on an object . This relationship is described by Newton's second law of motion, which states that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass.

The equation of motion to find the velocity of the dart when it leaves the gun.

The equation of motion is given by:

v = sqrt(2 * k * x / m)

v is the velocity of the dart

k is the spring constant (33 N/m)

x is the compression distance of the spring (0.03 m)

m is the mass of the dart (0.013 kg)

Substituting the values into the equation

v = sqrt(2 * 33 * 0.03 / 0.013) = sqrt(1320 / 0.013) = sqrt(101538.46) = 318.38 m/s

So the velocity of the dart when it leaves the gun will be approximately 318.38 m/s.

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an irregularly shaped object that is 10 m long is placed with each end on a scale. if the scale on 19) the right reads 96 n while the scale on the left reads 71 n, how far from the left end is the center of gravity of this object?

An irregularly shaped object that is 10 m long is placed with each end on a scale then the center of gravity is about 0.713 meters from the left end of the object.

To find the distance of the center of gravity from the left end, we can use the principle of moments, which states that the sum of moments on one side of a fulcrum must equal the sum of moments on the other side.

Let x be the distance from the left end to the center of gravity, and let the total weight of the object be W. Then the moment on the left side of the fulcrum is 71x, and the moment on the right side is (W - 96)(10 - x).

Setting these moments equal, we get:

71x = (W - 96)(10 - x)

Expanding the right side and simplifying, we get:

71x = 960 - 86x + 10W

Rearranging and using the fact that W = mg (where g is the acceleration due to gravity and m is the mass of the object), we get:

x = (10W - 960)/(71 + 86) = (10mg - 960)/157

Plugging in the given values of 96 N and 71 N for the scales, we can find the weight W as:

W = (96 + 71)/9.81 ≈ 16.14 kg

Plugging this value into the equation for x, we get:

x ≈ 0.713 m

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the most important factor about the classical conditioning is not how often the UC and the UCS are paired but how well the CS predicts the appearance ofthe UCS.

Not how frequently the UC or UCS are linked to velocity , but rather how well the CS anticipates the appearance of the UCS, is the crucial aspect of classical conditioning.

As a result, someone traveling through space at the speed as light experiences any time at all, or is rather frozen in time. The fact that there is no more pace to also be gained if we are going totally across space explains why we cannot speed faster than the rate of light.

The goal of this experiment was to look at how safety and conditioned fear (CS+ and CS—) cues affected open-field behavior. While the CS— boosted exploratory activity and decreased symptoms of fear, the CS+ reduced exploration , increased freezing time, and increased the amount of feces.

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Two masses (mA = 4 kg, mB = 10 kg) are connected via a light string around a solid disk pulley (mp = 1 kg, rp = 20 cm). Assume the pulley is frictionless. The coefficient of static and kinetic friction between all surfaces is 0. 2 and 0. 1 respectively. The angle θ1 = 30º while θ2 = 55º. (a) Use the Related Quantities sensemaking technique to compare (hint: maximum) forces within the system and determine whether the blocks accelerate when started from rest. (b) What is the angular acceleration of the disk? (c) What is the tension in the string on both sides of the pulley? (d) If the system starts from rest, how far does block A travel in 3 s. (e) After 3 s what is the angular velocity of the disk

Angular acceleration is 10.44 and a 93.96 angular velocity .

The rate at which the angular velocity changes over time is known as angular acceleration .

The rate at which an object's angular location or orientation varies over time is measured by its angular velocity .

Newton's second law of motion is applied to rotation by starting with the law of translation and substituting torque for force and mass for moment of inertia:

α = [tex]\frac{a}{rp}[/tex]

α = 2.09/0.2

It is reasonable to presume that angular velocity is likewise requested at the conclusion of the t=3 s interval because this question was asked in conjunction with question (c).

The following is the result of the equation for angular velocity as a function of Angular acceleration : ω= 93.96

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When two vehicles collide, momentum is conserved _______.a)if the collision is elasticb)only if deformation of either vehicle does not occur.c)if the collision is inelastic.d)whether the collision is elastic or inelastic.

When two vehicles collide, momentum is conserved whether the collision is elastic or inelastic. Option D is correct.

Momentum conservation is a fundamental principle of physics that states that the total momentum of a system is conserved if no external forces are acting on the system. In other words, the total momentum of a system before a collision is equal to the total momentum of the system after the collision.

This applies regardless of whether the collision is elastic or inelastic . In an elastic collision, both kinetic energy and momentum are conserved. In an inelastic collision, some kinetic energy is transformed into internal energy, causing the objects to deform or stick together, but the total momentum is still conserved.

Hence option D is correct.

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  1. Speed of light

    The speed of light in vacuum, commonly denoted c, is a universal physical constant that is exactly equal to 299,792,458 metres per second (approximately 300,000 kilometres per second; 186,000 miles per second; 671 million miles per hour). According to the special theory of relativity, c is the upper limit for the speed at which conventional matter or energy (and thus any signal carrying ...

  2. Speed of light: How fast light travels, explained simply and clearly

    In fact, we now define the speed of light to be a constant, with a precise speed of 299,792,458 meters per second. While it remains a remote possibility in deeply theoretical physics that light ...

  3. How fast does light travel?

    The speed of light in a vacuum is 186,282 miles per second (299,792 kilometers per second), and in theory nothing can travel faster than light.

  4. Speed of Light Calculator

    The final step is to calculate the total distance that the light has traveled within the time. You can calculate this answer using the speed of light formula: distance = speed of light × time. Thus, the distance that the light can travel in 100 seconds is 299,792,458 m/s × 100 seconds = 29,979,245,800 m. FAQs.

  5. Will Light-Speed Space Travel Ever Be Possible?

    The idea of travelling at the speed of light is an attractive one for sci-fi writers. The speed of light is an incredible 299,792,458 meters per second. At that speed, you could circle Earth more than seven times in one second, and humans would finally be able to explore outside our solar system. In 1947 humans first surpassed the (much slower ...

  6. Why is the speed of light the way it is?

    Light travels through space and its speed is independent of space itself so, for instance, as it passes near a star or blackhole and space is warped, it doesn't slow down or speed up, though its ...

  7. What is the speed of light?

    So, what is the speed of light? Light moves at an incredible 186,000 miles per second (300,000 kilometers per second), equivalent to almost 700 million mph (more than 1 billion km/h). That's fast ...

  8. Speed of light

    A Missy Elliott Song Travels to Venus at the Speed of Light speed of light , speed at which light waves propagate through different materials. In particular, the value for the speed of light in a vacuum is now defined as exactly 299,792,458 metres per second.

  9. What is the Speed of Light?

    Speed of Light ( c ): Light travels at a constant speed of 1,079,252,848.8 (1.07 billion) km per hour. That works out to 299,792,458 m/s, or about 670,616,629 mph (miles per hour). To put that in ...

  10. What Is the Speed of Light?

    The speed of light is the rate at which light travels. The speed of light in a vacuum is a constant value that is denoted by the letter c and is defined as exactly 299,792,458 meters per second. Visible light, other electromagnetic radiation, gravity waves, and other massless particles travel at c. Matter, which has mass, can approach the speed ...

  11. Three Ways to Travel at (Nearly) the Speed of Light

    The theory of special relativity showed that particles of light, photons, travel through a vacuum at a constant pace of 670,616,629 miles per hour — a speed that's immensely difficult to achieve and impossible to surpass in that environment. ... A well-aimed near-light-speed particle can trip onboard electronics and too many at once could ...

  12. All About the Speed of Light and What It Measures

    It is often stated that the speed of light is constant and that nothing can travel faster than the speed of light. This isn't entirely accurate. The value of 299,792,458 meters per second (186,282 miles per second) is the speed of light in a vacuum. However, light actually slows down as it passes through different media.

  13. Is There Anything Faster Than the Speed of Light?

    The speed of sound travels at around 343 m/s, while the speed of light travels at 299,792,458 m/s. In miles per hour/mph, the speed of light is at around 670,616,629, while in kilometers per hour, light travels at 1,079,252,848. In terms of seconds, light travels at around 300,000 kilometers per second or 186,000 miles per second in a vacuum.

  14. Physics Explained: Here's Why The Speed of Light Is The ...

    Today the speed of light, or c as it's commonly known, is considered the cornerstone of special relativity - unlike space and time, the speed of light is constant, independent of the observer. What's more, this constant underpins much of what we understand about the Universe. It matches the speed of a gravitational wave, and yes, it's the ...

  15. How "Fast" is the Speed of Light?

    How "Fast" is the Speed of Light? Light travels at a constant, finite speed of 186,000 mi/sec. A traveler, moving at the speed of light, would circum-navigate the equator approximately 7.5 times in one second. By comparison, a traveler in a jet aircraft, moving at a ground speed of 500 mph, would cross the continental U.S. once in 4 hours.

  16. How does light travel?

    So how does light travel? Basically, traveling at incredible speeds (299 792 458 m/s) and at different wavelengths, depending on its energy. It also behaves as both a wave and a particle, able to ...

  17. Scientists Believe Light Speed Travel Is Possible. Here's How

    Here's How. Scientists Believe Light Speed Travel Is Possible. Here's How. A functioning warp drive would allow humans to reach the far ends of the cosmos in the blink of an eye. n late 2020 ...

  18. Light Speed

    Light Speed. Light is fast! It can reach the universal speed limit — 186,000 miles per second. (If you could travel as fast as light, the universe would look very different.) Because it moves so quickly, light can seem to appear instantaneously. Think about when you turn on a TV... images pop up right away.

  19. How to Travel at (Nearly) the Speed of Light

    The theory of special relativity showed that particles of light, photons, travel through a vacuum at a constant pace of 670,616,629 miles per hour — a speed that's immensely difficult to achieve and impossible to surpass in that environment. Yet all across space, from black holes to our near-Earth environment, particles are, in fact, being ...

  20. Do all frequencies of light have the same speed?

    The speed of light in vacuum is constant and does not depend on characteristics of the wave (e.g. its frequency, polarization, etc). In other words, in vacuum blue and red colored light travel at the same speed c.. The propagation of light in a medium involves complex interactions between the wave and the material through which it travels.

  21. Can anything travel faster than the speed of light?

    When light travels through a vacuum, however, the same is not true. "All light is a type of electromagnetic wave, and they all have the same speed in a vacuum (3 x 10^8 meters per second).

  22. Why does time change when traveling close to the speed of light? A

    If you were traveling in a rocket moving at 75% of the speed of light and your friend throws the ball at the same speed, you would not see the ball moving toward you at 150% of the speed of light.

  23. What Would Happen If You Traveled At The Speed Of Light?

    When you traveled to Mars at 90% light speed, humanity on Earth was older by 16.67 minutes, while you aged by just 8.33 minutes! This difference in aging would become much more pronounced at higher speeds, say at 99.99% the speed of light. At 99.99% Speed Of Light. Now, suppose you could travel at 99.99% of the speed of light.

  24. Faster-than-light

    In the context of this article, "faster-than-light" means the transmission of information or matter faster than c, a constant equal to the speed of light in vacuum, which is 299,792,458 m/s (by definition of the metre) or about 186,282.397 miles per second. This is not quite the same as traveling faster than light, since:

  25. How Fast Is Warp Speed In Star Trek?

    The actual name is Time-Warp Factor, shortened to Warp Factor, usually shortened even further down to just Warp. It is a form of faster-than-light travel, allowing the interstellar travel that Star Trek is so famous for.. Without travel at the speeds that Warp allows, travel from one star system to another would take years at a minimum.It's why other sci-fi shows or movies without Warp show ...

  26. Basic Rules for Dungeons and Dragons (D&D) Fifth Edition (5e)

    The rules for determining travel time depend on two factors: the speed and travel pace of the creatures moving and the terrain they're moving over. Speed. Every character and monster has a speed, which is the distance in feet that the character or monster can walk in 1 round.

  27. NASA Sends a Missy Elliott Song to Space

    The July 12 transmission, announced by NASA on Monday, was made at the speed of light by a 112-foot-wide radio dish near Barstow, Calif. It took the song 14 minutes to travel 158 million miles to ...

  28. How Many Nanoseconds Does It Take Light To Travel 1.0 Km In A Vacuum

    The speed of light is 3344 nanoseconds per second. How many miles per second is light speed? 186 thousand miles per second. Fast is light! The maximum speed it can go is 186,000 per second. (The cosmos would appear radically different if one could move at the speed of light.) Light flows so swiftly that it might appear to appear instantly.