The speed of light is a fundamental universal constant that marks the maximum speed at which energy and information can propagate. Its value is $299792458\frac{\mathrm{m}}{\mathrm{s}}$.

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Interaction speed between electric charges and magnetic materials

Einstein said that the speed of a matter in universe cannot exceed the speed of light. Is it correct for electric force transmission speed from one electric charge to other one? What is ...
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Is a photon “fixed in spacetime”?

From what I've read, according to relativity, a photon does not "experience" the passage of time. (Can we say there is no past/present/future for a photon?) Would it be better to say a photon is ...
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340 views

Fermat principle: which index of refraction?

I am somewhat puzzled by a common formulation of the Fermat principle (light travel time), because it contains index of refraction related to phase velocity while light travel time through a slab of ...
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3answers
2k views

Will free-fall object into black hole exceed speed of light $c$ before hitting black hole surface?

In Newtonian mechanics, if we throw an object in against direction of gravity with speed $v$ and it achieve max height of $h$. Now if we allow object to fall from that height $h$, it will eventually ...
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528 views

Does gravity travel at the speed of light? [duplicate]

Whenever I did calculations in high school physics involving gravity, it was either "a ball falling to the earth" type scenario, or a basic measurement of the gravitational attraction between two ...
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3answers
1k views

Special Relativity and $E = mc^2$

I read somewhere that $E=mc^2$ shows that if something was to travel faster than the speed of light then they would have infinite mass and would have used infinite energy. How does the equation show ...
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1answer
313 views

What would happen to electronic circuits when traveling near the speed of light?

Imagine a space ship, loaded with all sorts of computer systems, traveling near the speed of light. Electricity itself is very fast, and can reach speeds close the speed of light. (up to 99% ...
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147 views

Why is neutrino beam not considered light?

I am trying to understand why physicists consider a neutrino beam not to be light. Here's the research that I did to find the answer: ...
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2answers
64 views

Does the efficiency of radiation change in any way in the presence of a medium?

I've read that radiation doesn't really require a medium. But if you're taking, for example, the sun's light, then does its efficiency of transmission increase or decrease once it reaches the earth's ...
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4answers
338 views

Faster-than-$c$ photons

As far as I know, according to quantum field theory, there are some photons that go faster than c, which is the speed of light in vacuum. However, there seems to be a paper and a corresponding ...
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Einstein's Gedanken Experiment that lead to the Special Theory of Relativity

Once, I read that Einstein founded the special relativity theory by imagining how an observer moves at the speed of light. How does this thought experiment work? How to reach from this imagination to ...
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Why does wavelength change as light enters a different medium?

When light waves enter a medium of higher refractive index than the previous, why is it that: Its wavelength decreases? The frequency of it has to stay the same?
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1answer
310 views

Can Mirror box simulate long light travel?

Imagine that there is a cube box that has mirrors all 6 faces in . If we use a strong laser and enter in the box from a small hole on the box. The laser light travels in the box long time that we can ...
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Is the universe a quantum computer - is light speed barrier a computational constraint

There is currently a debate ongoing on leading maths blog Gödel’s Lost Letter, between Gil Kalai and Aram Harrow, with the former arguing that building a quantum computer may not be possible due to ...
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3answers
480 views

What is the reason behind specific values for charge of electrons, protons?

Why do things like protons and neutrons have specific values. Also speed of light is a speed in which even if you go towards it, the speed does not vary. But why does light have to travel at speed?
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What is the proof that the universal constants ($G$, $\hbar$, $\ldots$) are really constant in time and space?

Cavendish measured the gravitation constant $G$, but actually he measured that constant on the Earth. What’s the proof that the value of the gravitation constant if measured on Neptune would remain ...
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4answers
776 views

The speed of tachyons

The other day I was wondering: When a tachyon is coming towards you faster than the speed of light, will you see it before it hits you? Then I thought of course not, since the light waves aren't ...
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3answers
606 views

Can a photon be emitted with a wavelength > 299,792,458 meters, and would this violate c?

Just curious if the possibility exists (not necessarily spontaneously) for a photon with a wavelength greater than the distance component of c to be emitted, and would this inherently violate the ...
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251 views

Why is $c$ considered as the speed of the photons?

Maxwell equations brought $\ c_{o}=\frac{1}{\sqrt{\mu_{o}\varepsilon_{o}}}\ $. Since this is a constant, it made all physicists at that time wonder where was the frame of reference? They ended up with ...
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6answers
4k views

Do photons have acceleration?

Photons travel at the fastest speed in our universe, the speed of light. Do photons have acceleration?
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2answers
727 views

Can the expansion space time reverse itself and contract the same way?

If there's a mechanism for space-time expanding faster than the speed of light, is there an example of It contracting in the same manner? If whatever mechanism is causing it to expand, can the ...
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5answers
607 views

Is there a universal rest frame of reference?

I am still struggling with C being a constant and what that implies. So can an experiment be done to find the resting state for the universe? Take a device with an observer and a light source and two ...
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2answers
278 views

What is the relationship between the speed of light and virtual particle production

What is the actual basis of the speed of light? Why is the transfer of information limited to it? Virtual particles that arise and disappear within a certain timeframe, is There a relationship ...
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2answers
254 views

light travels a maximum speed… /? [duplicate]

Possible Duplicate: Is it possible for information to be transmitted faster than light? we know that speed of light is an unconquerable term in physics..light takes about 1 year to travel ...
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3answers
960 views

What is the meaning of speed of light $c$ in $E=mc^2$?

$E=mc^2$ is the famous mass-energy equation of Albert Einstein. I know that it tells that mass can be converted to energy and vice versa. I know that $E$ is energy, $m$ is mass of a matter and $c$ is ...
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3answers
762 views

In a universe where the speed of light is infinite, are relativistic models and Newtonian models equivalent?

Take our universe. Observations are consistent with relativity, but not consistent with Newtonian mechanics. Assume that our current (relativistic) model of gravitation is correct. Now increase $c$ ...
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4answers
664 views

Reducing General Relativity to Special Relativity in limiting case

I understand that general relativity is applicable to gravitational fields and special relativity is applicable to case when there is no gravity. But is there a derivation on how to reduce General ...
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2answers
199 views

What will happen if we use a speed greater than light speed and find a body'motion and energy relative to it?

In Einstein's papers, he used light speed as a reference speed. What if we use a greater finite speed and do the same calculations. Won't this greater speed then be the limit.
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Why don't quantum effects invalidate the speed of light barrier?

While proving that no matter can reach the speed of light (a fact which I call the kinetic energy barrier), Einstein uses the fact that he can calculate the velocity and position of an electron. ...
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1answer
163 views

The range of light

It occurs to me that the empirical evidence shows that there is a point out in space where light stops coming from. Putting aside the expansion of the universe for a second, and focusing strictly on ...
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10answers
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Does the Pauli exclusion principle instantaneously affect distant electrons?

According to Brian Cox in his A night with the Stars lecture$^1$, the Pauli exclusion principle means that no electron in the universe can have the same energy state as any other electron in the ...
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1answer
2k views

How did Rømer measure the speed of light by observing Jupiter's moons, centuries ago?

I am interested in the practical method and I like to discover if it is cheap enough to be done as an experiment in a high school.
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1answer
212 views

Light vs neutrino speed comparison in a real tunnel

Given current accuracy of the techniques, is it possible to identify a real, existing tunnel (stright I think) to make the direct comparison of the speed of light and of neutrinos? The hypotetical ...
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3answers
460 views

How do physicists justify using $c^2$ in equations?

Excuse my ignorance but I see physicists use $c^2$ in equations and I was wondering what reasoning they use to justify $c^2$ since, as far as I understand, $c^2$ must be an absurd quantity because ...
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6answers
606 views

When has the speed of light been measured, recently?

Yes, it is weird, absurd, but I can't stop thinking that the would-be superluminal neutrino speed has been computed by an arithmetic operation (space/time) and not by direct comparison with a ...
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5answers
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Why are $\mu_0$ and $\epsilon_0$, which appear in electrostatics and magnetostatics, related to the speed of light which appears in electrodynamics?

$\epsilon_0$ and $\mu_0$ appear in electrostatics and magnetostatics. When we include time varying fields we have electrodynamics and the appearance of c which turns out to be related to $\epsilon_0$ ...
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1answer
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How light years is measured? [closed]

How are light years are measured? I remember the distance between earth and moon are measured by the delay in light which travels and comes back. But how are light years calculated?
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What if we could give photons some mass?

I was reading an article and these paragraphs got me wondering... Before I list the replies, here is some background. The Higgs mechanism describes an invisible field that, it is argued, split one ...
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420 views

Speed of Light, Photons or WaveSpeed?

The speed of light is almost 300 000 km/s. The photons have a speed along the wave, and the wave have a speed straight forwards. What is the speed of light? Is it the speed the photons have along ...
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2answers
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why is mechanical waves faster in denser medium while EM waves slower?

Why is it that mechanical waves/longitudinal waves/sound travel faster in a denser/stiffer medium as in steel compared to say air, while EM waves/trasverse waves/light travels slower in a (optically) ...
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1answer
214 views

$E=mc^2$ why is it $c^2$ and not just $c$?

Why is constant for the conversion of mass to energy square of the ligths speed? is it bedside it's the fastest real matter? .
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2answers
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What are the implications of the speed of light broken? [duplicate]

Possible Duplicate: What would be the effects on theoretical physics if neutrinos go faster than light? I don't know if it's been asked before, but I couldn't find a thread about it. I ...
8
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2answers
650 views

Do gravitational waves slow down as they pass through matter?

I've heard that gravitational waves travel at the speed of light, and have some parallels to electromagnetic waves. EM waves slow down as they pass through matter (speed of light in glass is slower ...
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2answers
449 views

Does gravitational differences affect the distance light travels? (a thought experiment)

My question is: How is light passing through different gravitational densities affected? The value of "c" is constant in a vacuum. I'm curious about if various time frames have any effect. This is ...
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2answers
559 views

What happens to body chemistry at the speed of light? [duplicate]

Assume that I'm traveling at the speed of light in one direction. My brain is also traveling at the speed of light in that direction. Presumably there is at least one receptor site in my brain that is ...
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4answers
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Does a photon in vacuum have a rest frame?

Quite a few of the questions given on this site mention a photon in vacuum having a rest frame such as it having a zero mass in its rest frame. I find this contradictory since photons must travel at ...
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2answers
1k views

At what fraction of the speed of light have people traveled?

I'm guessing that, this would be someone in a rocket or something... When they hit their top speed, at what fraction of $c$ are they traveling?
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3answers
369 views

Does the Special Theory of Relativity “form” the foundation of Modern Physics?

Does the Special Theory of Relativity "form" the foundation of Modern Physics? My question is in reference to Geoff Brumfiel's Scientific American article "Particles Found to Travel Faster than Speed ...
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4answers
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Why is the speed-of-light “the upper limit” rather than the speed of “particle type X”?

Basically, I can't stop wondering why light (the photon) is so special, compared to all the other particles known (and unknown) to modern day physics. Could it be that there exists an upper limit on ...
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1answer
216 views

The relation between the speed of light and the Big Bang Theory

I would like to know how much of the Big Bang theory is dependent on the constancy of the speed of light. P.S.: It might be guessed that I am asking this because of the recent CERN news. Yes, of ...