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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2answers
583 views

Do neutrinos travel faster than light in air?

I read in wiki that the speed of light is 88km/s slower in air than it is in a vacuum. Do neutrinos travel faster than light in air?
0
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1answer
82 views

Acceleration reaches speed of light? [duplicate]

Hi, I am thinking about acceleration. Let's think we have a force of $1$ N and a particle of $1$ kg, then acceleration will be $1$. So the speed gets higher every second and $c$ seconds later, in ...
5
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5answers
631 views

Does a photon instantaneously gain $c$ speed when emitted from an electron?

An excited electron looses energy in the form of radiations. The radiation constitutes photons which move at a speed $c$. But, is the process of conversion of the energy of the electron into the ...
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1answer
62 views

Speed of light energy

Considering the amount of energy necessary to accelerate a particle to the speed of light (ie; half the energy in the entire universe) how could we have so many things already going the speed of ...
0
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2answers
145 views

Time Delays in General Relativity

If gravity propagates at, or less than, the speed of light, and is therefore not instantaneous, does that introduce time delays to gravity? For example: suppose that we, the observer, sit within the ...
0
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2answers
872 views

Nothing can travel faster than the speed of light. In what frame of reference? [duplicate]

Since frames of reference are arbitrary, I can define a frame of reference that moves backwards with a speed greater than $c$, then any static object in that frame of reference is already traveling ...
0
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1answer
115 views

Special Relativity Time problem

Suppose there are two observers, they each own a light clock which were synchronised in the beginning and are moving relative to each other. So each of them accuses that the other person's clock is ...
0
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2answers
55 views

How fast does the collapse travel in a multiple slit experiment?

If we have a kilometer long million slit light source and make an observation on a slit at one of the ends, will the interference pattern fully collapse or partially collapse? is there any delay in ...
35
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7answers
7k views

Why does the speed of light in vacuum have no uncertainty?

I could understand that the definition of a second wouldn't have an uncertainty when related to the transition of the Cs atom, so it doesn't have an error because it's an absolute reference and we ...
3
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2answers
764 views

The famous drop of $c$

In this, in my opinion, intriguing speech, Rupert Sheldrake, tells the story of the drop between the measured valued of $c$ in 1928 and 1945. When he goes to visit the Head of Metrology of the Physics ...
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2answers
182 views

Paradox Regarding Time Dilation at the Speed of Light

Consider the following scenario: On earth, I pulse a laser focused at a far away mirror such that the time it takes for the light to reflect off the mirror and arrive back at me is at least a few ...
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3answers
524 views

Why Sun light can reach us if Time is dilating?

I understand that if something is moving with constant speed in respect to an observer, the time of the moving one runs slower, so the more your speed is, the more your time ticks slower. Which ...
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2answers
829 views

Why can't matter pass the speed of the light? [closed]

I have the following questions. Why can't matter pass the speed of the light? What happens to an object when it comes close to the speed of the light? What makes the object unable to surpass this ...
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1answer
124 views

Physical meaning of the Rindler hyperbola vertex and the Rindler lines

Two questions regarding the Rindler diagram: 1) Does the vertex of a given hyperbola in the diagram have physical meaning? I know it is the inverse of the constant proper acceleration ($\alpha$) ...
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2answers
294 views

Reflection between two mirrors?

If I put my hand between two perfectly aligned mirrors and then remove it will the images continue to reflect for a few nanoseconds? If yes then will the images be of a combination of the front and ...
0
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1answer
1k views

Why does light travel at finite speed? [duplicate]

We have known for quite some time now that light travels at a finite speed of 3x10^8m/s (approx) through vacuum. But why is that? Why can't the speed be infinite? Or at least higher than the current ...
-1
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1answer
138 views

If the universe can expand at a speed faster than that of light, why don't we feel the effect? [closed]

the universe, as I have read, is capable of inflating at a speed faster than that of light! How is that even possible if we don't feel the effect? or does it affect us?
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5answers
913 views

What does 99.9% speed of light mean when there is no absolute velocity?

So when people say: 'I am approaching the speed of light, and to get to 100% light I would need infinite energy' they are essentially saying that this situation is impossible? I read this in ...
4
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4answers
401 views

Speed of light travel

I have just started special theory of relativity. The limiting speed known as speed of light fascinated me most. I asked my teacher: Consider two massless objects moving in the same direction at ...
3
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1answer
1k views

Didn't Newton's Corpuscular theory fail to explain reflection?

In 1637 Descartes gave the corpuscular model of light and derived Snell's law. This Corpuscular model of light was further developed by Isaac Newton in his famous book entitled OPTICKS and because of ...
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1answer
120 views

At what frequency does the medium of air change from acoustic to light?

I'm calculating the max doppler frequency of a fading channel in an in-room environment and looking at different carrier frequencies. Calculated as follows: F = vf/c Where F -> max doppler shift v ...
11
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4answers
3k views

Do all massless particles (e.g. photon, graviton, gluon) necessarily have the same speed $c$?

I suppose there was a discussion already on speed-of-gravity-and-speed-of-light. But I silly wonder whether all the massless mediators of four fundamental forces, i.e. Graviton: $g_{\mu\nu}$ ...
11
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2answers
1k views

How is it possible the universe expanded faster than the speed of light during inflation?

In a documentary written in collaboration with Stephen Hawking, the narrator (supposedly Stephen Hawkings) says that by the time the cosmos was 10 minutes old, it had already expanded thousands of ...
0
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1answer
58 views

How is the universe is experienced at light speed? [duplicate]

When moving faster, we experience time dilation and space contraction. We often state that a photon does not travel through time, i.e. if it where capable of observation, it would not experience time. ...
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1answer
240 views

Faster than light possibility? [duplicate]

According to general relativity, speed is relative, so for example if you are running at 20 km/h and a car passes you at 30 km/h, the runner is actually moving at 50 km/h relative to the car. Now ...
2
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1answer
78 views

Slowing of photons in a EB Condensate

Help me understand this. I have heard tell that they are now able to slow the forward progress of a photon traveling through an EBC to somewhere near 35mph. Is this actually the physical slowing down ...
0
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3answers
159 views

Is light slower when traveling inside a gravity field?

This question is not about phase velocity changed which causes refraction, but about the real time itself being slower by the gravity of any object (from general relativity). If so, would this mean ...
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1answer
337 views

Lorentz boost matrix in terms of four-velocity

As I understand it, the value of a 4-vector $x$ in another reference frame ($x'$) with the same orientation can be derived using the Lorentz boost matrix $\bf{\lambda}$ by $x'=\lambda x$. More ...
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0answers
65 views

Clocks tick steadily, so why is there no photon time? [duplicate]

Consider a photon bouncing left and right between two mirrors in a photon clock. Seen from inside the clock, the photon bounces at a constant frequency. Time ticks regularly. No matter whether the ...
0
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1answer
251 views

What is the significance of Einsteins postulate on speed of light?

Einstein postulated that the speed of light in free space is the same for all observers, regardless of their motion relative to the light source, where we may think of an observer as an imaginary ...
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2answers
251 views

Proving invariance of $ds^2$ from the invariance of the speed of light

I've started today the book of Landau and Lifshitz Vol.2: The Classical Theory of Fields $\S 2$. They start from the invariance of the speed of light, express it as the fact that $$c^2(\Delta ...
4
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2answers
755 views

Did Einstein know about Michelson-Morley experiment?

The second postulate of special relativity deals with constancy of light in inertial reference frames. But, how did Einstein came to this conclusion? Did he knew about the Michelson-Morley experiment? ...
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1answer
46 views

Su­per­lu­mi­nal in­ter­ac­tions

The fact that photons emitted from an electric-dipole active atom cannot be spatially localized better than to the near-field zone of the atom is seen as the origin of genuine superluminality. ...
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3answers
263 views

Velocity of the photon

As far as I know photon travels in a wave pattern, that means it has $x$ and $y$ axis velocity components. If photon travels along $x$ axis, then what is it's maximum $y$ axis velocity?
0
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1answer
163 views

Concentration of photons: How many can you slow down in a given unit of space?

Being able to slow down light to the speed of a bicicle as shown in this vid: http://www.youtube.com/watch?v=EK6HxdUQm5s Led to a question: Given a unit of space e.g. 1cm^3, and then you slowed down ...
4
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2answers
199 views

Speed of light, lasers and mass

Hopefully this isn't a bad question. Light travels at the speed it does and nothing else can travel that fast because things have mass, correct? Or at least correct on an elementary level. And if ...
13
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1answer
463 views

Is it only the Higgs field that stops me from getting to $c$?

Is it only the higgs field that stops me from accelerating up to the speed of light or is there other restriction concerning the increase in mass? In other words if I had a Higgs field shield on my ...
2
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5answers
378 views

How can I explain this fallacy of conveying information faster than Light?

First statement of this question: In superluminal phase velocities, what is it that is traveling faster than light? says that information cannot be transmitted at a velocity greater than speed ...
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1answer
58 views

Does photons undergo the process of cyclic absorption and re-emission by virtual particles in vacuum?

The process of cyclic absorption and re-emission by electrons in a medium is an explanation for the fact that light appears to slow down in mediums relative to vacuum. But, does light undergo this ...
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4answers
540 views

Why is the speed of light considered as a fundamental constant if its speed changes with medium resulting in refraction? [duplicate]

I know that the speed of light, the universal constant of gravitation and the Planck's constant are considered to be the three fundamental constants of the universe. But, why is speed of light ...
2
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2answers
214 views

does light experience time? [closed]

If we positioned a mirror 1 light year away from earth and shot a particle of light at the mirror so that it would reflect and come back to earth, how long would it take for us to receive that ...
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0answers
208 views

Is false vacuum bubble nucleation possible in our universe?

Is it possible that a false vacuum bubble to nucleate into our universe rather than a true vacuum one ? If yes,it will expand at speed of light within our spacetime or what ?
1
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1answer
54 views

The speed of light and fields

Does the speed of light apply to the speed of (waves?) in every known field, or does it only apply to the electromagnetic field?
3
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1answer
215 views

Time dilation and the speed of light in the twin paradox

Suppose we look at the twin paradox where the twin traveling at high speed relative to an observer on earth has a clock which counts time by sending photons of light across a distance within the ...
3
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8answers
21k views

How does velocity cause time dilation?

I've been trying to learn about the speed of light and time dilation, but I'm at an impasse. The presented facts say that if I travel around the solar system at 50% the speed of light and then come ...
3
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0answers
49 views

Momentum of light in medium [duplicate]

Maybe this has been asked before, but I didn't find anything about it. I am wondering about the momentum of light in media with refractive index n>1 (so to say, not in vacuum). There are two ...
1
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2answers
180 views

Variance in speed of light

While discussing this question (Does light have an unending journey?) I stumbled on the fact that light's speed is constant only in inertial frame. What I happened to do was add up the expansion of ...
-1
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2answers
875 views

How is the speed of light an absolute maximum speed in the universe? [closed]

Under the heading which came first, the chicken or the egg, which came first: the maximum velocity of electrons orbiting the atom, or the speed of light as the maximum velocity limit? Is it possible ...
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2answers
404 views

Does influence on gravity increase with mass when velocities approach the speed of light? [duplicate]

In other words, when a particle's mass increases significantly as it approaches the speed of light (c), does its influence on gravity increase, and if so, does it increase proportionally?
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1answer
261 views

What do subatomic particles look like for a 'speed of light - observer'?

Let's say that an observer is moving with the speed of light relatively to an atom that he wants to look into. He has equipment that precise that he can observe the atom and what is inside. From ...