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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How the speed of light is constant in the universe if it decreases in water and glass and some other objects? [duplicate]

My teacher told me that speed of light is constant in the universe. But in optics it is clearly shown that speed of light slows down in some objects. Please help.
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3answers
148 views

From the photons perspective

Probably been answered but couldn't find the answer. From the perspective of a photon: - For the photon to travel from body A to body B would take 0 secs. - The universe would be one point in "...
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1answer
92 views

Why phase velocity of light is slower in a dielectric than vacuum?

Why does light speed suffer a reduction when it passes through a homogeneous dielectric medium? I know my math says so, i.e.- a highly polarizable ($\chi$) medium is associated with high $\epsilon$ (=$...
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1answer
139 views

Is max speed of causality (light) proven experimentally?

Is it possible to have an alternative theory which is consistent with experiments supporting GR, but which doesn't mandate a speed limit on causality? In other words, I understand there is ...
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0answers
32 views

How come an electron's wave function being nonzero at far distances doesn't mean it can travel faster than light? [duplicate]

I think the wave function of a free electron is nonzero almost everywhere. In particular there are regions of space arbitrarily far away where the electron has positive probability of being found. If ...
2
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1answer
68 views

A rope between Earth and Moon - Length and Speed of Light [duplicate]

An earlier question was asked on what would happen if a rope was attached between Moon and Earth, but the question was more about the impacts in terms of geology. We keep the same experiment setup : ...
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1answer
48 views

Hows does one account for the speed of light delay in field equations?

Suppose I have a simple time varying classical field $\vec{f}$. The force of the field on an object with a charge $X$ at a position $S$ is: $ \vec{F_f}\left( t \right) = X \vec{f}\left( t \right) $ ...
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1answer
30 views

Limitations of radiowave speed [closed]

If radio waves travel as fast as light, how was nixon able to talk to the apollo moon crew in real-time over a phone? it seems this concept makes the idea of seeing something billions of light years ...
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2answers
81 views

If curved paths imply that the vehicle is accelerated, how come do we assume that light gets curved whilst its speed is constant?

I don't understand how we can accept these two sentences at the same time: Light speed is constant, therefore experiences no acceleration. On the presence of a gravitation field, light path is ...
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1answer
71 views

Why aren't we all moving at the speed of light relative to photons? [duplicate]

Using basic logic.... We know speed and velocity is relative. My point is if we take our speed with respect to a photon moving in opposite direction we are practically moving at speed greater than ...
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0answers
45 views

What will the point of view be when you move faster than light in a medium?

In water the light become slower to the point where electron in water moving faster than light (in the same medium). So in electron frame of reference what will electron's point of view be? From what ...
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1answer
65 views

Question regarding the mass of an alpha particle when travelling at a speed approaching the speed of light [duplicate]

The speed of an Alpha particle is: 10^7 m/s. This is a speed approaching the speed of light. hence, should the (relativitic) mass of the Alpha particle vary?
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1answer
60 views

how photon gets accelerated instantaneously to speed of light? [duplicate]

i understand that the photon when emitted is already travelling in the speed of light but how can it go from 0 to speed of light instantaneously. is it because photon is a mass less particle and the ...
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1answer
58 views

Can we really predict for distances 100s of light years away? [closed]

I read this article today http://timesofindia.indiatimes.com/home/science/8690kmph-winds-discovered-on-exoplanet/articleshow/49789687.cms?utm_source=facebook.com&utm_medium=referral&...
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1answer
72 views

How can we say that difference in energy between 99.99% and 100% of speed of light is infinite? [duplicate]

How is it not possible for a particle to attain 100% speed of light and what will happen if it attains the speed of light?
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1answer
41 views

How can the speed and the mechanics of light be similar to the speed and the mechanics of gravity? [duplicate]

How can the speed and the mechanics of light be similar to the speed and the mechanics of gravity? Most say that light cannot escape a black hole. Then gravity cannot escape a black hole either, so ...
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5answers
5k views

Could gravity accelerate light? [duplicate]

Gravity causes anything with energy to accelerate toward the source. Black holes, for example, have such strong gravity that they pull in light and don't let any escape. But can acceleration still ...
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1answer
121 views

Take advantage of time dilation or create a warp drive? [closed]

It is my understanding that time dilation slows down perceived time relative to the outside of a given vessel as it approaches the speed of light. Does that not mean that the inhabitants of said ...
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4answers
859 views

Why only higher energy photons can affect atoms even though their speed is same? [closed]

I understood that a baseball moving at the cosmic speed limit can do lot of harm, but since photons are not comparable to a baseball so irrespective of their high speed they do not rip anything in ...
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1answer
48 views

Coordinate Time and Proper Time/Simultaneity [closed]

At close to the speed of light, clock A is running slower than "stationary" clock B. Does clock A enter the future time reference of clock B as it slows down? Trying to understand where the forward ...
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1answer
81 views

Relativity: easy spaceship scenario. easy questions [duplicate]

Your spaceship is traveling at 1/2*c and you approach Bob's spaceship going -1/2*c in the opposite direction. Relative to you, Bob is going the speed of light, and of course he has a giant ticking ...
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3answers
59 views

What prevents me to accelerate an object to near light speed in space?

As far my limited knowledge go, things in space aren't slow down unless something interferes with them, so what prevents me to build a spaceship powered by nuclear power that will keep accelerating ...
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56 views

Flagpole/shadow trig relationship question but accounting for real speed of light

So in high school everyone has solved the trig problem of relating the height of the flagpole (h), the length of its shadow (l), and the angle at which the sun rays are striking the flagpole (ϕ). (...
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2answers
96 views

How we are able to see stars in night, even if they are light years away from earth? [closed]

I am wondering, how we are able to see so much stars in the sky even though they are light years away from us. Even light take years to reach from those stars to earth? Then, how we are seeing those ...
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1answer
51 views

Extra mass due to near light like speeds [duplicate]

Why does mass seem to increase as you near the speed of light?
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1answer
38 views

How long will the light exist inside the sphere?

Ok, so let's say we have a very thick, but hollow, metal sphere. The inside of the sphere has a radius of 100 meters. The sphere also has a door that can be opened and closed and when closed makes an ...
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1answer
71 views

Speed of light, velocity limits and superluminal travel [closed]

I know that a massive object cannot reach the speed of light as it would require an infinite amount of energy to do so (though my knowledge of the reasons of this phenomenon is very limited). Couldn'...
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1answer
42 views

How soon would electrons start flowing once I closed a switch on a circuit that was one light minute away from the battery

In a circuit, how do electrons "know" when the circuit is closed? To my understanding, they do not start flowing unless the circuit is closed. How soon would they start flowing once I closed a ...
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1answer
125 views

Time dilation: linear or exponential or other?

As you near the speed of light, time slows for you relative to the world around you. So you would be traveling at more than one hour per hour. Is the rate of time slowing for you linear or exponential ...
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1answer
76 views

How fast is the speed of light in vacuum? [closed]

If we were to travel the speed of light how many times will we be able to orbit the earth in 1 hour? Also how long will it take to make 1 orbit at the speed of light?
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1answer
71 views

How can we see the alien, who are travelling in light speed? [closed]

If aliens has the technology to travel in speed of light ,How can we see them with our 'below the speed of light' technology?. Because when we see that(!),definitely it will not be in its place.Is ...
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2answers
83 views

How does a flash of light appear to a high speed observer

Imagine two dark chambers separated by a light-proof partition each with a 30m high ceiling. Chamber A has a letter A painted in white on its black ceiling, chamber B has the letter B also in white on ...
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3answers
185 views

Speed of light and vision lag [closed]

A lot of the answers here are for the question below but the previous question has not been received well. So with the same question in mind, wouldn't the universe look different from different parts ...
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2answers
65 views

Why wasn't the theory that light's velocity depended on its source very popular?

Before special relativity, it was believed that light having a specific velocity meant it had to travel through something. My question is, why wasn't the idea that light depended on its source very ...
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3answers
101 views

Speed of electricity in cable [duplicate]

Movement speed of electricity in cable, is same as speed of light in space? In other words, electricity moves in usual electro cable aproximatelly 300 000 km/second ?
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0answers
42 views

Speed of Light with trains [duplicate]

Suppose that there is a train (train1) going at 100 km/h. The train is infinitely long. Suppose that there is an other train inside train1 (train2), which has a speed of 100 km/h also. So for a ...
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1answer
110 views

Feynman lectures on physics: The Michelson-Morley experiment

I have a problem understanding something. I'm reading FLP and here I don't understand why when the system is travelling, the light doen't make the same angle in the mirror C... if B and C are moving ...
2
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1answer
326 views

Does the Michelson-Morley experiment disprove gravitational waves?

I may be misunderstanding gravitational waves, but doesn't the idea of a gravitational wave imply that spacetime is a field or "medium" through which waves propagate at speed $c$? Was not this idea ...
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0answers
28 views

Why is the speed of light constant in all inertial frames? [duplicate]

I know this is a physical principle and cannot be derived at from other physical laws. But how can it be arrived at? What observations or what train of thoughts leads to this conclusion? e.g. the ...
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1answer
126 views

Did the mass of the electrons went infinite in the experiment done by William Bertozzi in the 1960s?

it is impossible to accelerate a particle to a speed greater than c, no matter how much kinetic energy we give it In an experiment published in 1964, electrons were accelerated to a large voltage ...
2
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2answers
132 views

Speed of light in zero-index material or similar

I've always thought that the maximum speed of light is achieved in vacuum. Now in some "popsci" news there are references as if there are mediums where light can go faster. Are these zero-index ...
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4answers
317 views

Why can't anything travel faster than light?

It is a well known fact, that nothing can travel faster than light. I have discussed that fun fact numerous times with my 8 year old son. One day he asked "why?", and I realized that I didn't know the ...
2
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3answers
378 views

Relative Time from a far place

I have read that whenever we see the sun we are seeing the sun as it was before 8 minutes ago. Meaning if the sun were to somehow go dark we would not know until 8 minutes after. Now I became ...
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0answers
29 views

Reaching the speed of light [duplicate]

This is a very elementary question, and I'm sure there's a simple answer. However, I must ask... So I had this random thought... Imagine you had a bullet that would fire an additional bullet. Just ...
2
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2answers
137 views

The Michelson-Morley experiment

A fundamental assumption in special relativity is that the speed of light is constant in all inertial reference frames, which was first established empirically via the Michelson-Morley experiment. ...
0
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1answer
87 views

How can light cross $c$ in the given hypothetical experiment? Where I am wrong? [closed]

There is a concave mirror, which has somehow maintained the speed $\frac{c}{2}$ toward west ( for instance) , and there is a light wave or you can say a ray of light is moving in N-E direction. So we ...
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2answers
274 views

How long would it take to see the nearest star die?

If you were in the general proximity to the nearest star to Earth (besides the Sun) and you saw it turn to a neutron star or black hole at the very end of it's star cycle, how much longer would it ...
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2answers
126 views

Why is the speed of light a limit? and why is it just $3×10^8\,\text{m/s}$? [duplicate]

Why does light travel with speed $3×10^8\,\text{m/s}$? and why not more?
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2answers
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Will light continue traveling after the source has stopped producing light? [closed]

Will light continue traveling after the source has stopped producing light?
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1answer
104 views

How can travelling at light speed affect light itself? [duplicate]

~Hypothetical Scenario: Your driving in a car (with the headlights on high beam) and you gradually get faster until you reach the speed of light. Raised Assumptions: You can see in and out of the ...