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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What wilI I observe when travelling at almost the speed of light? [duplicate]

If I and a group of friends are travelling at or just below the speed of light - can I see myself, can I see them, or they me? Would we see anything at all?
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If something is not moving in space, is it moving on the time axis at the speed of light? [duplicate]

I heard this theory yesterday: If something is not moving in space, then it is moving on the time axis at the speed of light. I realize that in essence there is no object which can be considered as ...
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41 views

How can light have the same speed for all observers? [duplicate]

I'm a little confused on this. If you're travelling at, say, 10% of the speed of light then light is travelling at 3x10^8 ms^(-1) relative to you. If you're moving at 80% of the speed of light and ...
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Breaking the speed of light…? [duplicate]

I know the speed of light can't be broken, but I cannot figure out why the following scenario is not possible. I'm not a physicist myself but I know the basic stuff. Assume you're in a car ...
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Does the Doppler effect disprove the constancy of $c$? [closed]

Why doesn't the Doppler effect disprove the relativity postulate that $c$ is constant relative to all sources or observers? It seems it does because of the following example: Suppose a ship of ...
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Is there a difference between the speed of light and that of a photon?

As in the title I am curious whether there is a difference between the speed of photon and the speed of light, and if there is what is the cause of such a difference?
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Can time pass for a photon if it's moving in a medium? [duplicate]

If time does not pass for a photon traveling at the speed of light, which can only occur when traveling in a vacuum, what happens when it is slowed down by traveling through non vacuum space like ...
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If rest mass does not change with $v$ then why is infinite energy required to accelerate an object to the speed of light?

I know that as the velocity increases, the mass of the object also increases so it becomes tougher and tougher to move the object which ultimately leads to a requirement of infinite energy to ...
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Special relativity and missing factors of $c$

I am doing problems in a textbook called 'Introduction to Classical Mechanics' by David Morin. In one of the questions it says the following: In the lab frame, two particles move with speed $v$ ...
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Velocities of waves (such as visible light, and radio)

The speed of light in a vacuum is a constant 299,792,458 m/s. In water, it is much slower. Does this happen to such waves as radio, or X-ray? (Would say, a 3 meter wavelength travel slower in air than ...
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Is the amount of radiation you receive in space constant regardless of velocity?

I'm only in high school, so this will probably have fatal flaws. So basically in space, there is bound to be stray radiation, whether from the stars, or cosmic background, floating around right. And ...
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Accelerating beyond the speed of light? [duplicate]

Suppose you have a lot of fuel in your spaceship, in deep space - enough to accelerate at 1mss for a long time. What would happen once you are travelling close to the speed of light? Could you reach ...
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Why don't clocks on a train read the same time?

Two clocks are positioned at the ends of a train of length $L$ (as measured in its own frame). They are synchronized in the train frame. The train travels past you at speed $v$. It turns out ...
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How can a particle in a medium ever travel faster than light? [duplicate]

In some media, mass-carrying particles can go faster than light: Cherenkov radiation, ... is electromagnetic radiation emitted when a charged particle... passes through a dielectric medium at a ...
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What made Einstein to figure out speed of light is constant? [duplicate]

I have gone through the answers to the questions on the similar lines, but I am not fully satisfied with them, I want to dig deep into this assumption because it is a very strong assumption. If ...
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Did Newton argue that particles speed up when entering a more dense medium?

Statement: Newton argued that particles speed up as they travel from air into a dense, transparent object, such as glass. From this source, I gather that he did argue that the light particles ...
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Lightspeed (invariance) measurement methods

I would like to know, how measurements of the speed of light are conducted these days, especially in the context of the invariance of $c$. Do all the methods involve mirrors to redirect the photons ...
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Special Relativity, 2nd Postulate — Why? [duplicate]

As a lowly physics undergrad who has been chewing on this 2nd postulate of special relativity for a year or more, I simply can't wrap my head around reasons why it is true or how Einstein might have ...
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The Equivalence Principle approaching the speed of light [duplicate]

If, in local system, an accelerated system is completely physically equivalent to a system inside a gravitational field. Acceleration results in an increase in speed. Right? What happens when the ...
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Doppler Shift when Light Travels Through Two Different Mediums

When considering the Doppler shift, the 'canonical equation' is $$f=\frac{c+vr}{c+vs}f_0$$ However, this equation seems to run into trouble in the following situation: A light source inside water is ...
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What is light and how does it travel? [duplicate]

My question is: What is light, and, more specifically, how does it travel? I've been contemplating a theory that I watched on Youtube (which has no real credibility to my knowledge), the Cosmic ...
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42 views

How can light travel at speed of light? [duplicate]

I am well aware that the speed of light is a universal constant at which nothing but light can travel. But why? Why can even light travel at such a speed? Our maths tell us that anything with rest ...
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Speed of light in general relativity

My question has a few parts concerning the speed of light in general relativity. Firstly, time changes in response to gravity and speed. Therefore, as gravity effects time in an area of space, should ...
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Expanding universe and the speed of light [duplicate]

When physicists talk about the expanding universe they often say that the distant galaxies are not really "moving" away but instead the space itself between us and them is expanding. If this is true ...
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265 views

Energy & Mass of a Photon [duplicate]

$$\text{Please read the whole question before answering}$$ Before I ask my question, I would like to say that "Yes, I do know a photon has no mass." I was helping someone here on P.SE with the ...
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Approaching speed of light: why do objects appear further away in front of me?

A Slower Speed of Light is a video game created by the MIT Game Lab which allows users to experience what it would be like if the speed of light was closer to normal walking/running speeds and thus ...
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What causes light to travel? [duplicate]

What is the force that causes it to move and why does it maintain the speed for so long? If it has no mass, why is it effected by mass?
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A curious case of Relativistic Velocity Addition [duplicate]

The relativistic velocity addition formula is $$u = \frac{v+u'}{1+ \frac{vu'}{c^2}}$$ Where $u$ = velocity of projectile seen by rest observer "A" $v$ = velocity of moving observer "B" as seen by ...
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Is light so important in special relativity?

I'm an amateur physics enthusiast with no formal university education in Physics. So my question might sound very naive, so forgive me. I had this question in the back of my mind since the wrong ...
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When gravity pulls on light it blueshifts or redshifts it, which way around does it go?

when light is propagating away from a mass does it get blue shifted or red shifted? And if its going towards a mass whats the effect?
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Speed of light and distance

Our measure of distance (the meter) is defined in terms of how far light in a vacuum travels in a specific time. When light travels through another medium, we say it travels at a different speed. Why ...
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35 views

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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162 views

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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51 views

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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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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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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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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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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98 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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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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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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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 ...