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

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How does light travel at the speed of light? [duplicate]

If it is impossible for matter to accelerate to $c$ (because doing so would take infinite energy), and if light can be deemed matter (because of wave-particle duality, photons are matter, right? And ...
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Is time nothing but the speed of light (or the light itself)?

With regard to relativistic effects on time, all the examples and explanations revolve around light and its speed. Especially in explanatory situations that explain this using photon clock, it seems ...
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Does this count as moving faster than light?

I'm not familiar with any complicated physics equation, however I do understand some basics. Suppose there is two objects, both of them are moving away from each other in a 3-dimensional space, which ...
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Universal speed limit [duplicate]

Is there any reason the universe has matter not being able to exceed the speed of light, or why there is a speed limit in the first place? I know why it can't, meaning the basic physics of it. I ...
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1answer
58 views

If the mass of an object or system is a measure of its energy content, multiplied by speed of light squared…?

If the mass of an object or system is a measure of its energy content, multiplied by speed of light squared, does it mean that the total potential energy of the rest mass of object or entire system ...
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Which electromagnetic radiation is faster in water, microwaves or light?

Well I've been asked this question, but I haven't been able to come with an answer yet using books and some web searches. The point is as the title says, to answer the question with the whole ...
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How did Fizeau make his famous speed-of-light experiment?

I heard once in a TED talk how Fizeau measured the speed of light in the 19th century. Here is the link https://www.youtube.com/watch?v=F8UFGu2M2gM You can read about it here in Wikipedia: ...
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What is the derivation of the speed of light $c$ that is not based on electromagnetism? [duplicate]

The "speed of light" is not just the speed of electromagnetic radiation, but of any massless particle. Therefore must not there be an expression for $c$ that is not in terms of $\mu_0$ and ...
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Can you run away from your shadow?

Now this might be a silly question but it's actually bugging me, this one might be easier to understand if you have kids that watch (or used to watch) Peppa Pig. In one of the episodes, about shadows, ...
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86 views

Speed of light versus pull of gravity - Is $c$ really the limit? [duplicate]

The understanding I have is that the speed of light is considered to be the highest attainable speed in physics. Of course there are theories of tachyons but since those haven't been proven we'll ...
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If we could reach very high speeds, could we measure the velocity of the Earth this way?

If we could reach (nearly) the speed of light with spaceships, could we measure the velocity of the Earth by launching three perpendicular rockets, accelerating them, and measuring how much fuel ...
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Which of these theories on why light slows in media are true?

This question is similar to previously asked questions, but the responses to them are confusing and I think it may be better covered by listing out all the potential answers for clarity. It's a ...
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22 views

Dissipating light pollution

If all the lights in a city, and the area surrounding it were shut off. How long would it take for the light pollution to clear, so the light from stars could be seen?
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31 views

Is there any acceleration of light? [duplicate]

I find it hard to believe that photons always travel with 3 x 10^8 m/s just from the start. But there must be some acceleration of light. Maybe huge or taking place in picoseconds. So what maybe the ...
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80 views

Maximum speed higher than the speed of light

I wanted to ask if higher speed than the speed of light will be discovered, will scientists be able to adjust the special relativity to the new situation? I read that informations transmitted faster ...
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Consistency of the Speed of Light [duplicate]

My question is simple and possibly stupid, but I wanted to know hypothetically what would happen if two objects start moving away from each other at half the speed of light (0.5c). Is the observed ...
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3answers
305 views

Does the the quantum field theoretic process of particle–antiparticle annihilation break the axioms of Special Relativity?

$\textbf{Note that this diagram hasn't anything to do with the question directly.}$ After a particle and its antiparticle annihilate, their energy is converted into a force carrier particle, such ...
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1answer
78 views

Travelling at/over speed of light, I fire a laser in front of me. What happens to the light from the laser? [closed]

For a moment, assume that travel at/over the speed of light is possible, and we fire a laser in front of us, what happens to the light emitted from the laser? Would the photons scatter, or would the ...
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1answer
16 views

Relation between intensity of light and refractive index

The intensity of light (as calculated from time average of the poynting vector) is given by $I = (1/2) \epsilon v E_0^2$. Here the intensity is dependent on the velocity of light in the medium. The ...
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What is $c + (-c)$?

If object A is moving at velocity $v$ (normalized so that $c=1$) relative to a ground observer emits object B at velocity $w$ relative to A, the velocity of B relative to the ground observer is $$ v ...
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1answer
58 views

If gravitational radiation (or anything) cannot escape a black hole, how can it produce redshift or curve spacetime? [duplicate]

There is an apparent paradox in a Black hole. Keenan Pepper wrote: Electromagnetic radiation cannot escape a black hole, because it travels at the speed of light. Similarly, gravitational ...
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Perception when Moving at the seed of light? [closed]

Let us assume that a person moves at the speed of light say towards a planet -say Neptune. Neglecting the relativistic mass effects of the person, what would be his perception? In Vsauce- a YouTube ...
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2answers
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How can individual photons have different amounts of energy?

If photon is an elementary particle, how can different photons have different energy, if $E=mc^2$ and all photons have (or don't have) the same mass and the speed of photon is constant shouldn't it ...
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1answer
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What is the speed of light from a star moving towards a observer.? [duplicate]

We can say that in vacuum speed of light is constant. But if the star is moving with a certain velocity does it add that velocity to the velocity of photons emitted out of that star?
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What makes photons travel at the speed of light? [duplicate]

Photons are the only elementary particles which can travel at speed of light. What are the qualities of the photon that enable it to travel with the speed of light?
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Why does light travel at the same speed when measured by a moving observer? [duplicate]

I know the hypothesis that the light speed is constant is retained by experiments. But is there any theory explaining why the light speed is constant no matter how an observer moves relative to light? ...
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$F=ma$ calculation taking relativity into account?

Newton's second law of motion states that $f = ma$. However, in this equation, theoretically there could be a value of $f$ and $m$ that results in an acceleration that is enough to push an object past ...
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Which experiment would be able to detect change in the speed of light? [duplicate]

Since the unit of distance is defined in terms of speed of light in vacuum, if the speed of light in vacuum were to change by "magic", what experiment would be able to detect that? Is there a theory ...
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Is speed of light and sound rational or irrational in nature?

Just as circumference of circle will remain $\pi$ for unit diameter, no matter what standard unit we take, are the speeds of light and sound irrational or rational in nature ? I'm talking about ...
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Massless particles and the speed of light - New? Theories of existence [closed]

"The best understanding we have is that it [light] is a disturbance in the electromagnetic fields of charged bodies." http://einstein.stanford.edu/content/relativity/q212.html This is a link to the ...
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1answer
115 views

How does it seem to be that space/time always equals c?

Given the way objects move, they seem to be going all the same "velocity" so to speak, that velocity being the speed of light. Except, velocity is displacement/time, so if something goes faster, the ...
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5answers
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Why Light and Observers have different laws of physics [closed]

Special relativity states: The speed of light in a vacuum is always $c$, regardless of the velocity of the observer. The laws of physics are the same for all observers in uniform motion. These two ...
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Does Light (EM Signal) undergo accelration during reflection? [duplicate]

Since Average acceleration is defined as, Average acceleration over a period of time is the change in Velocity divided by the Duration of the Period. Does Light (EM Wave) undergo acceleration during ...
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Experiment with spring and two light sources emitting light in opposite directions

Two (almost massless) light sources connected with a (almost massless) spring emit light beams in opposite directions. What is the speed at which the spring extends?
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Do the laws of physics that apply to all observers also apply to a non-observer? [closed]

The Timelessness of a photon https://www.youtube.com/watch?v=5ELA3ReWQJY An observer's laws of physics are time based. "When you're traveling at the speed of light, time does not exist" - Neil ...
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Does physics recognize the particle of light separately from the wave of light? [closed]

To frame this question, we need to assume that time freezes when traveling at the speed of light. This is theoretically congruent with Einstein's theory of relativity and the theory of time dilation, ...
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Are the ideas of the speed of light and the absolute top speed inside the universe equivalent? [duplicate]

The idea of the speed of light being as fast as something can go is pretty well accepted. I'm wondering if the top speed might be (very slightly) higher? Lemme explain. I was reading about particle ...
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Is the Speed of Light an universal spacetime constant, the velocity of electromagnetic waves, or of photons?

This question has been touched tangentially by What's a better phrase than "speed of light" for the universal spacetime speed constant? and Could light travel more slowly than the ...
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What would the properties of a particle be that would allow light to orbit it? [duplicate]

What would the properties of a particle be that would allow light to orbit it? Light travels fast. Really fast. Almost to the point where we consider that it's instantaneous, and moves only in a ...
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3answers
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Why do we say that light travels at a speed? [duplicate]

According to Einstein's theory of relativity, the more speed something has the slower that time passes for it; and presumably when traveling at the speed of light, time stops entirely. So this means ...
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156 views

What is the difference between “accelerating a particle to light speed” and “turning on a flashlight”?

According to how we understand the universe it would take an infinite amount of energy to accelerate the ambiguous "particle" to light speed. Yet there are all kinds of reactions that cause light, ...
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7answers
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Relativity of Simultaniety

In the first figure, A and B are two equidistant points from the observer O in S. In the second figure (reference frame S') the corresponding points are A'and B' such that A'O'=O'B', where O' is the ...
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Would computers accelerated to high speeds compute “faster” from our point of view?

I woke up to this thought yesterday: Lets say Computers A and B have exactly the same specifications and at time T both are set to process an algorith that would normally take exactly 1 year and ...
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About star groupings and there apparent positions in the sky

Imagine a group of 3 stars that appear to be equally luminous ,star A, B, and C in the shape of an isosolese triangle. Imagine A that appears at the 'top' of the triangle is 100 light years away . B ...
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79 views

Problem on speed of light

As I was reading special relativity, my book says the speed of light is $c$ with respect to any other thing. Does that mean the speed of an individual photon is $c$ even with respect to another ...
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117 views

Why doesn't light travel instantly? [duplicate]

I've read that the faster you travel in space, the slower you travel in time. And when you reach the speed of light (which we won't be able to) time will stand still. So when light travels at the ...
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Is speed of light invariant in different inertial frame?

Don't get angry at me. I believe in special relativity just as any scientist would. But reading this article http://arxiv.org/abs/0708.2687 I realize that actually I haven't done any experiments on ...
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Can special relativity be extended such that the frame of a photon makes sense?

Suppose I want to know what the universe looks like from the perspective of a frame of reference moving at $c$ relative to my current frame. As discussed at length in various other questions on this ...
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Twin Paradox Without Acceleration

So I've been doing a lot of reading about the twin paradox and have encountered several different explanations that strive to resolve it. First off let me start by saying general relativity is not an ...
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2answers
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Equilibrium: Inertia & Applied Force

Thank you for taking the time to read this. I am lay and will understand if the question is closed. My understanding is that in a vacuum, a constant force of $n$ applied to an object of mass $m$, ...