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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If time stops for an object, does that object feel gravity?

As far as I understand The GTR, it is said that Mass bends space-time which causes gravity. So every Mass in this universe is flowing through space-time example earth is moving along with space-time ...
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how can u control the speed of light? [closed]

The light traveling a 3 lake km/sec, but Pls tell me how can a control the speed of light, means can limit the speed like 2 lake km/sec are 1 lake km/sec Pls tell me equation
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191 views

Can a force stop a Photon since Photons have momentum and What does momentum mean when talking about massless particles?

Momentum measures how hard it is to stop an object. While Photons are massless they still have relativistic mass and energy. My question is can something stop photons other than being absorbed by ...
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2answers
94 views

Is it possible for a photon to be at rest? [duplicate]

I know it doesn't really make sense if looking at the photon from the wave point of view, but is there any law of physics which prohibits a photon from stopping completely? Thanks.
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1answer
131 views

Accelerated Light Sources

When someone accelerates towards a light source, how does the light that's radiating off from it look? I suppose in an inertial frame, all the light should be moving off straight from the source, but ...
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92 views

Are we travelling at a speed close to the light speed? [duplicate]

This is a question which has been puzzling me quite a while. There was a news report saying that the farthest galaxy spotted so far is at 13.3 billion light-years away, and it is said that the galaxy ...
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1answer
388 views

Why an electron “rotate” around the nucleus at a speed close to the light one? [closed]

Why an electron "rotate" around the nucleus at a speed close to the light one? I mean where he gets all this energy? One DOES NOT simply approach the speed of light AFAIK.
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1answer
111 views

Are there (or could there be) electrically charged particles that move at the speed $c$? [duplicate]

A photon, a neutrino (if it has zero rest mass) move at $c$ but what about charged particles? If the answer is no, is there a fundamental reason or just because of the radiation it emits?
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61 views

Is the universe we know just shaped due to time? [closed]

Call me a daydreamer, but I could not stop myself for asking this question. I was idle when something ticked me and struck my head. I was thinking about universe, speed of light, and how time works. ...
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3answers
427 views

Two different mediums can have equal index of refraction?

In other words: given a certain medium, is light's phase velocity unique?
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2answers
1k views

Do radio waves go faster than the speed of light? [closed]

My science teacher used to say a lot of weird stuff, but I'm just making sure on this one.
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1answer
361 views

Frame of reference of the photon? [duplicate]

In the frame of photon does time stop in the meaning that past future and present all happen together? If we have something with multiple outcomes which is realized viewed from such frame? Are all ...
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2answers
174 views

How did the scientific community receive this measurement of speed of gravity

This link and this one concern a recent measurement, by Chinese scientists, of the speed of gravity using Earth tides. They find it is consistent with a speed equal with the speed of light, with an ...
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2answers
737 views

reflection at speed of light when both mirror and viewer is travelling at the speed of light [duplicate]

consider me sitting on the top of a train which is travelling close to the speed of light, will I be able to see my image on a mirror which I'm holding in my hand??
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4answers
247 views

How does light behave within a black hole's event horizon?

If the event horizon of a black hole is the distance from the center from within which light cannot escape, imagine a person with a flashlight falls into the black hole. He points his flashlight in a ...
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1answer
81 views

Use something that slower than light in Michelson–Morley experiment

Follow by the Michelson–Morley experiment, What happen if we use something that has a speed lower than light instead of light in Michelson–Morley experiment? How about the result?
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1answer
91 views

Speed of Light Question and Einstein [closed]

Einstein's clock experiment. What would happen if you were to travel at the speed of light or faster than the speed of light towards the clock? Can we translate this into traveling large distances ...
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1answer
191 views

Simple Question: Speed of Electromagnetic Waves in a Medium

If the speed of an electromagnetic wave in a particular medium is such that $v = c$, the speed of light, does this mean that the permeability $\mu = \mu_0$, i.e. that of a vacuum and the index of ...
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5answers
238 views

Is velocity of light constant? [duplicate]

There is a difference between the concept of the speed of light and the velocity of light. are both of them constant ($dc=0$ and $dv_c=0$)? if yes, why?
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What exactly is implied by Einstein's insight in this scene from the NOVA series “$E=mc^2$ Einstein's Big Idea?” [closed]

In the documentary movie "$E=mc^2$ Einstein's Big Idea?", the narrator says "Einstein had a monumental insight", when Einstein and his close friend were looking at the clock towers in the city. ...
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2answers
121 views

Relative to the speed of light

Einstein's relativity tells us that light always travels at the speed of light relative to me, no matter how fast I'm going. Right? This really confuses me though. If light travels from A to B in one ...
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1answer
132 views

Can a pushed plank beat light and break the laws of physics? [duplicate]

Imagine you are one lightyear away from a photon sensitive (light sensitive) switch. So it is obvious that light would take one year to reach to the switch. Now I have a one lightyear long plank. I ...
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2answers
249 views

What is the time component of velocity of a light ray?

If we have a light ray $x^\mu$ with velocity $c$, what is $c^0$ (the time component)?
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1answer
110 views

Is it possible to make a light beam act like a stream of water from a spining hose? [closed]

If we had the ability to make an actuator that could turn around at or past the speed of light and I attached a high miliwatt laser to it, then spun the laser around on the actuator at the speed of ...
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1answer
134 views

The Speed of Light [duplicate]

I know that the speed of light is constant for some reason. But why is it that when shining light from a spacecraft that is moving at (almost) the speed of this light, the speed of this light ...
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1answer
136 views

Quantum Mechanical Effects of an object accelerating near speed of light $c$?

Consider a space ship, undergoing constant acceleration (which for our purposes means that the same amount of energy is being used per second to increase its speed). According to special relativity ...
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Points in Spacetime

Assume there are two points in spacetime $a=(t,x,y,z)$ and $a'=(t',x',y',z')$. Let's say that the first one is in the origin of spacetime i.e. $a=(0,0,0,0)$. The point $a'$ has two possibilities ...
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Does the expansion of the universe soon after the Big Bang affect the amount of time that light takes to reach us?

If faster than light travel is impossible, how is it that light emitted from matter so close together in the time soon after the Big Bang is only now just reaching us? I would assume that there would ...
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69 views

Solar sail area going to Proxima Centari [closed]

I have a physics question that I need some help with: "Proxima Centauri is a star in the Alpha Centauri solar system, it’s the nearest star to our sun (4.24light−years) ...
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41 views

Black hole and photons [duplicate]

I've read in a book that even light can't escape the gravitational pull of a black hole after a certain distance. But this seemed impossible to me. Imagine a photon, moving directly in the opposite ...
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1answer
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Does the magnitude of a mass affect the velocity?

Imagine that I shrink my entire mass to fit within the volume of a light particle. If I was then 'hit' by another light particle would my greater mass affect my gain in velocity from this collision ...
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4answers
944 views

What causes the permittivity and permeability of vacuum?

When light travels through a material, it gets "slowed down" (at least its net speed decreases). The atoms in the material "disturb" the light in some way which causes it to make stops on its path. ...
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2answers
171 views

Superluminal particles with causality

What kind of CLASSICAL theories would allow to true (non-apparent) superluminal particles (beyond speed of light, BSOL) agreeing with causality to exist? I mean, are causal superluminal classical ...
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89 views

Relation of color and frequency for the visible spectrum

In this question the OP is looking for a way to see light that is outside of the visible spectrum without using electronic sensors. This got me wondering about the visible spectrum itself. Typically ...
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Describing physical constants in alternate wording; c = there can only be 671million miles of space for every second of time [closed]

This spawns from part of an answer to a question I asked. All sorts of things go to 0 and/or ∞ if you start boosting at c, and so you cannot boost into and out of a photon's frame. It ...
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1answer
101 views

Zero uncertainty constant and a unit change

So, we know the speed of light with zero uncertainty. We also know that values of $\epsilon_0$ (electric constant) and $\mu_0$ (magnetic constant) are known with zero uncertainty. My questions are ...
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129 views

Neutrinos and Speed of light

Einstein's Special Theory of relativity postulates that the speed of light is same for all frames. Suppose a neutrino is there moving at the speed of light. Then will that neutrino also be flowing ...
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79 views

Is there any proof that the speed of gravity is limited? [duplicate]

I must warn that though I'm argumenting with black holes I'm not asking how does gravity escape the black hole!. I want to know if the absolute speed of gravity waves were proven bu an experiment. We ...
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1answer
266 views

Why does Lorentz factor not hold for relativistic mass when we apply it to photons? [duplicate]

We know that the photon itself is massless particle $m_0=0$. But we also know, that the mass of the objects does increase with their energy. And we know that under certain circumstances (gravity, ...
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1answer
427 views

Could the shadow move with faster-than-light speed? [duplicate]

If I make a huge laser with a figure for shadow in front of the laser, and I shine it on to the moon, will I see the light from the laser AND the shadow moving the same speed? (I read somewhere the ...
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1answer
395 views

Could entropy explain dark energy? [closed]

This was 3rd beer idea, so please bear with me. What if the universe was not actually expanding but the speed of light was slowing? Wouldn't that be indistinguishable to our observations? Either way ...
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Reaching the speed of light via quantum mechanical uncertainty?

Suppose you accelerate a body to very near the speed of light $c$ where $v = c - \epsilon$. Although this would take an enormous energy, is it possible the last arbitrarily small velocity needed -- ...
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1answer
142 views

Is the speed of light related to the mass of the universe?

If the mass of the universe were cut in half, would it affect the speed of light? Would it be twice as fast? Would it stay the same? Do we have instruments that are sensitive enough to measure the ...
4
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1answer
81 views

Live feed from a Rocket traveling near the speed of light?

Okay, odd question popped up in my physics class today. If a rocket ship is traveling at .99c for 1 year, and is streaming a video at 30 frames/sec to earth, how would the earth feed be affected? ...
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How does this paper relate to standard QED?

This paper proposes a microscopic mechanism for generating the values of $c, \epsilon_0, \mu_0$. They state that their vacuum is assumed to contain ephemeral (meaning existing within the limits of ...
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3answers
191 views

Stuff can't go at the speed of light - in relation to what? [duplicate]

We all know that stuff can't go faster than the speed of light - it's length becomes negative and all kinds of weird stuff happens. However, this is in relation to what? If two objects, each moving ...
2
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2answers
269 views

Is Earth's orbit around the sun affected by the ~8 minutes light delay?

Gravitational change occurs at the speed of light. As a consequence, we experience on Earth the gravitational attraction of the sun based on its position relative to us ~8 minutes ago. How does this ...
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Michelson–Morley @ Home

The Michelson-Morley experiment seems to have taken many years, resources and a nervous breakdown to complete. Is it possible to recreate a variation of this experiment at home for say, under $1000, ...
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1answer
117 views

Magnets and speed of light

I am in no way a physicist but I do have a fascination with physics. My question is if magnets are being explored / studied as a potential source to achieve the speed of light and if that is even ...
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3answers
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What is the cause the light is affected by gravity? [duplicate]

I know that photons have no mass and that a photons exist only moving at the speed of light. So what is the cause that a massive astronomical object can bend a ray of light? I have two thoughts, but I ...