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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“If the astronaut found that light slowed down relative to his motion, he would have detected the very ether wind that Michelson failed to detect”?

The following extract is from Relativity Simply Explained by Martin Gardner (Amazon link): Consider an astronaut in a spaceship that is racing alongside a light beam. The ship is traveling with ...
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31 views

How to explain the homogeneity of the universe through a physic model [duplicate]

If in general, two objects homogenize themself by combining it's parts, why the horizon effect, based on a big bang model, excludes such an important physical interaction process? I wonder if this ...
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40 views

Constancy of speed of light $c$ with perpendicular motion [duplicate]

Suppose light is travelling in a straight line parallel to $y$-axis takes time $t$ to reach from $y_1$ to $y_2$ in a reference frame $S$. Let there be another frame, $S'$, which is travelling parallel ...
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271 views

How can the orbit of Jupiter's moons be used to calculate the speed of light? [duplicate]

How can the orbit of Jupiter's moons be used to calculate the speed of light? It seems this was one of the first methods and goes back to 1656.
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178 views

What's the max speed a man-made satellite can travel in space before its circuitry stopped working?

Assume it could withstand extreme temperatures in either direction. I'm mainly curious what would happen to its circuits as it approached the speed of light.
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242 views

Inertia on relativistic mass when particle is near speed of light

Inertia is directly proportional to mass but what happens when something travel to speed near to light. Its relativistic mass tends to infinity but that is false mass so I want to know if inertia is ...
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3answers
222 views

Is the speed of light in vacuum constant or does the math just happen to work out?

My apologies if my question is really idiotic, but I ask sincerely because I want to learn. Based on this question and lots of other places on the web, this topic seems to be really confusing. Let's ...
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5answers
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Is the speed of light in vacuum always the same value?

The escape velocity of different planets and stars vary. If they vary, the velocities of bodies escaping from the respective stars or planets should also vary. Like, if I want a ball to reach 10 ...
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1answer
171 views

Are we all moving at $c$? [duplicate]

Is it true to say that all matter in the universe is travelling with velocity c through spacetime, but that for baryonic matter most of that velocity is through the time dimensions rather than the XYZ ...
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2answers
83 views

Measurement of the speed of light form different perspectives

I've been showing a special interest in Einstein's theory of relativity and how he proved the speed of light to be always the same. At first it was a bit hard for me to understand, but now I THINK I ...
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1answer
39 views

How is it that the voltage wave along a circuit is a tenth of the speed of light?

I have heard that the voltage wave (pushing the electrons) along a circuit is a tenth of the speed of light. Can someone please explain with an illustration how it is possible?
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1answer
140 views

How do we know that fundamental constants don't slowly change in time? [duplicate]

Let me get one thing straight first. I am not saying that fundamental constants like the speed of light don't have the value that we know they have today. What I am asking is whether the value of a ...
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3answers
96 views

Would a giant see our year as a second? [closed]

If there were an enormous being whose arm span is one light year across, how would that being perceive time? Wouldn't what we perceive as a year be virtually nothing to that being? Explanation: "...
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Forces and the light

Do external forces can affect the light? Can any external force make the light accelerate? And if it can, will it accumulate mass? (according to the second Newton's law of motion $m = F/a$ ) We know ...
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186 views

Newton's laws and the maximum speed

According to Newton's second law of motion : $F = ma$ In an certain occasion, we exert 2 forces (the magnitudes of the forces are the same) on 2 different objects, Object A and Object B, in the same ...
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1answer
73 views

Light travels in a medium

According to Snell's law : $${n_1 \over n_2} = {v_2 \over v_1}$$ $v_2 = v_1 n_1 / n_2$ Assuming that $n_1$ is vacuum , we will find the following equation: $$v = c / n$$ (We may find the same ...
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Do you encounter more photons (per unit time) when moving forwards at a constant velocity?

Let's say you have rain hitting you evenly on all sides (not very realistic, I know). If you were to move forwards at a constant speed, there would be more droplets of rain hitting you per second on ...
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2answers
64 views

Why can't we increase the speed of sound in a constant Temperature-pressure condition?

We know the speed depends on the kinetic energy. Imagine that we have 3 iron balls equally spaced and kept in space (zero gravity condition). If i push the first ball slowly it would travel slowly ...
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73 views

Relative Velocity Problem: Light? [duplicate]

Assume 2 rockets coming towards each other at each other at 99% of speed of light, and so as they pass each other the relative velocity between 2 rockets would be 198% of Speed of Light and so what ...
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4answers
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How do I sum up speed though space and time to obtain c (in terms of units)?

I'm still learning SR and only recently I could scratch the surface of such beautiful, complex and deep topic. This post here was really enlightening, and even though it is somewhat basic, it helped ...
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If all motion is relative, how does light have a finite speed?

I've often heard that Einstein shattered the notion of absolute motion (i.e. all things move relative to one another) and that he established the speed of light as being absolute. That sounds ...
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2answers
64 views

Relativistic deceleration and energy

It's common knowledge that due to relativistic effects, accelerating from 0.8c to 0.9c takes a lot more energy than accelerating from 0.1c to 0.2c. However, what's the case with deceleration? Does it ...
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3answers
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The relation between mass and speed

Massless particles (or luxons) have no (rest) mass ($m = 0$) and a speed equal to the speed of light ($v = c$). Massive particles (or bradyons) have mass ($m > 0$) and a speed lower than the speed ...
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114 views

How is light slowing down in a medium thought of in the photon picture? [duplicate]

The speed of light in any medium besides vacuum is smaller than $c$. In a classical way, I just look at that as a wave that propagates less fast, the change in EM-field is passed on slower. How should ...
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5answers
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I know light's speed in vacuum is constant, but what about its velocity?

Is the velocity of light in vacuum constant? It seems it would be different depending on whether it is coming toward you or away from you, but I just want to make sure. Does the direction of light ...
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166 views

Is distance always 0 relative to an object moving at speed of light $c$?

As I understand it, when an object is traveling at the speed of light, relative to itself all travel is instantaneous and the distance is zero. If a photon traveling from the sun was aligned with the ...
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165 views

The invariance vs constancy of the speed of light in vacuum

This is perhaps as much a question of semantics as of physics but it is something I have been thinking about recently and was wondering if anyone else had a perspective on this. Now, it could be that ...
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158 views

The speed of light/EM waves in vacuum; as if there was another one in non-vacuum?

Q1: is there a speed of a photon other than in "vacuum"? Q2: isn't "speed of light in vacuum" misleading? If I understand, that light moves with speed of light until there is "something in between" ...
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1answer
144 views

On the no-faster-than-light in special relativity

In the special relativity it is well established that, in the vacuum no one can ever travel faster than light, due to the relativistic velocity addition formula. Recently I saw some silly statement ...
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175 views

Nothing can travel faster than the speed of the light, but could this be an exception? [duplicate]

I often show off by asking people how fast electrons flow through wires. Then I tell them it's actually only a few millimeters per second. To clear the disbelief off their faces and boost my ego, I ...
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1answer
58 views

Is it possible to travel forward and backward along with time? [closed]

Is it possible to travel along through time if we found a thing that is more speeder than light?
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4answers
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Why the speed of light in vacuum is same in all inertial reference frames? [duplicate]

If Cathy’s velocity toward Bill and away from Amy is v = 0.9c, Cathy finds, by making measurements in her reference frame, that the light from Bill approaches her at speed c, not at c + v = 1.9c. And ...
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Why $c$ is $3$ x $10^8$ times faster than a $1$ $m/sec$ car? [duplicate]

The value of of a dimensional constant like $c$ is often regarded as unimportant since it can be arbitrarily changed to any desired value by changing our units. For example, $c$=$3$x$10^8$ in $m/sec$, ...
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79 views

Michelson-Morley experiment

I have to do an experiment about light. I preferred to measure the speed of light by the experiment of Michelson and Morley. When you do the experiment, it will result in an interference pattern by ...
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2answers
115 views

Stopping a Body (travelling at the speed of light) [closed]

While, I read that if a body accelerates to the speed of light would have an infinite mass and therefore, infinite energy would be required to maintain the speed. A question popped up in my mind: ...
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What is $c$ in the Lorentz force expression?

The usual Lorentz force expression I am familiar with is this: $$\vec F=q(\vec E+\vec v \times \vec B)$$ I have seen some other versions lately that include an extra factor $1/c$: $$\vec F=q\left(\...
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Speed of light paradox [duplicate]

If I send two rockets from the Earth in opposite directions, at, say, 60% of the speed of light relative to the Earth, then relative to each other they are travelling at 120% of the speed of light. ...
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Why wouldn't any Emission Theory work?

http://www.pitt.edu/~jdnorton/teaching/HPS_0410/chapters/origins_pathway/#Emission Here, at the Emission theories of light, I loved the discussed theory. There seems to be a contradiction right ...
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Maxwell, speed of light and the electric permittivity and magnetic constants

When Maxwell found that the already-measured speed of light could also be derived from the already-measured electric and magnetic constants, what were the electric and magnetic constants measured to ...
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If the speed of light is constant in all reference frames, why does the mirror clock experiment show light travelling on an angle?

I was recently looking for answers as to why time slows down the faster you travel and regularly came across the mirror clock experiment. This experiment has a beam of light bouncing between two ...
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1answer
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Is it possible to apply force to a light particle?

I know, the universal speed limit is the speed of light $c$. So, is it possible to apply more force to a light particle? What would happen to it if we could?
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165 views

Travelling at a relative speed greater than the speed of light [duplicate]

I've wondered about this since I was a kid. I've been told the speed of light is a constant ($c$), which would mean that light always travels at the same velocity. Now, here's what interests me: if I'...
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1answer
58 views

Relativity and observable universe

Will cosmological horizon "expand" for an observer approaching the speed of light (at least in the direction of observer's motion) ?
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1answer
566 views

What would happen to the human body if we went almost at the speed of light? [duplicate]

If we were to travel almost at $299\,792\,458~m/s$, or the speed of light, what would happen to the human body? Would the human body stay the same or would there be consequences that would harm the ...
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2answers
169 views

Is speed of light is impossible, even for light in nature? [closed]

im not a student, teacher, researcher in fact I've never even taken a physics class. But I Love to argue!, i spent a day proving (in my mind anyway) that, 1. a photon does have mass. 2. its ...
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1answer
54 views

Camera on the ground vs camera in a train

A couple days ago my history teacher was explaining special relativity with the train example, where you are in a train close to light speed and you see a clock on the train terminal and the clock ...
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80 views

Light speed time distortion

From my understanding objects moving close to the speed of light experience a time distortion in that time moves slower and slower as they get closer to the speed of light. If that is the case shouldn'...
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78 views

Traveling near the speed of light

If I travel near the speed of light, form a stationary observer perspectives, I will take 1 year plus to travel 1 light year, but in my perspective, would I take less than 1 year to travel to that ...
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1answer
81 views

Is Lorentz transformation applicable of light itself?

I've just studied Einstein's Special Theory of Relativity and have followed most part of it. I was just wondering that whether the equations of Lorentz transformation are applicable on light? i.e. can ...
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Filming light in slo mo

So I was thinking of a cool video I could make when I thought of filming a video of me turning on a light. I thought that if you film yourself turning on a light and slo mo that video enough times (...