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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How does gravity escape a black hole?
My understanding is that light can not escape from within a black hole (within the event horizon). I've also heard that information cannot propagate faster than the speed of light. It would seem to ...
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13answers
7k views
Home experiments to derive the speed of light?
Are there any experiments I can do to derive the speed of light with only common household tools?
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12answers
2k views
Is it possible for information to be transmitted faster than light by using a rigid pole?
Is it possible for information (like 1 and 0s) to be transmitted faster than light?
For instance, take a rigid pole of several AU in length. Now say you have a person on each end, and one of them ...
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7answers
11k views
How can a photon have no mass and still travel at the speed of light?
I've read a number of the helpful Q&As on photons that mention the mass/mass-less issue. Do I understand correctly that the idea of mass-less (a rest mass of 0) may be just a convention to make ...
17
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3answers
821 views
Does gravity slow the speed that light travels?
Does gravity slow the speed that light travels? Can we actual measure the time it takes light from the sun to reach us? Is that light delayed as it climbs out of the sun's gravity well?
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1answer
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How did they measure the speed of light observing Jupiter's moons, centuries ago?
I am interested in the pratical method and I like to discover
if it is cheap enough to be done as an experiment in a high school.
Thank you.
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2answers
285 views
Does gravity travel at the speed of light?
Whenever I did calculations in high school physics involving gravity, it was either "a ball falling to the earth" type scenario, or a basic measurement of the gravitational attraction between two ...
15
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3answers
762 views
What is the length of 1 second in meters
If time is treated as a fourth dimension of spacetime, what is relation between length and time units?
Or in other words, how can I convert time units to length units, for instance seconds to meters?
...
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10answers
7k views
Does the Pauli exclusion principle instantaneously affect distant electrons?
According to Brian Cox in his A night with the Stars lecture$^1$, the Pauli exclusion principle means that no electron in the universe can have the same energy state as any other electron in the ...
13
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2answers
294 views
What does a sphere moving close to the speed of light look like?
What shape does the viewer in a reference frame with $v=0$ perceive? I suppose that since the sphere moves in one direction only (oX only, not oY) its section would change into an ellipse, where the ...
13
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4answers
445 views
What is the mechanism behind the slowdown of light/photons in a transparent medium?
So light travels slower in glass (for example) than in a vacuum. What causes light to slow down? Or: How does it slow down? If light passes through the medium, is it not essentially traveling in the ...
12
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3answers
97 views
If neutrinos travel faster than light, how much lead time would we have over detecting supernovas?
In light of the recent story that neutrinos travel faster than photons, I realize the news about this is sensationalistic and many tests still remain, but let's ASSUME neutrinos are eventually proven ...
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3answers
968 views
Is the universe a quantum computer - is light speed barrier a computational constraint
There is currently a debate ongoing on leading maths blog Gödel’s Lost Letter, between Gil Kalai and Aram Harrow, with the former arguing that building a quantum computer may not be possible due to ...
12
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3answers
878 views
Why the vacuum polarization does not decrease the speed of light?
On one hand, in the classical electrodynamics polarization of transparent media yields in lowering the speed of light by the factor of $n=\sqrt{\epsilon_r \mu_r}$ (refractive index).
On the other, in ...
11
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2answers
842 views
Is the “How to break the speed of light” minute physics video wrong?
I am referring to this video, on YouTube, by minutephysics, which has quite a lot of views.
In the video it states that if you flick your wrist while pointing a laser that reaches the moon, that the ...
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5answers
1k views
How do photons travel at a speed that should be impossible to attain?
If it requires infinite amount of energy to travel at the speed of light then how photon attains this speed? Its source is never infinitely sourced.
11
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2answers
641 views
Deriving the speed of the propagation of a change in the Electromagnetic Field from Maxwell's Equations
I've been told that, from Maxwell's equations, one can find that the propagation of change in the Electromagnetic Field travels at a speed $\frac{1}{\sqrt{\mu_0 \epsilon_0}}$ (the values of which can ...
11
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3answers
374 views
How does a photon experience space and time?
To an an external observer it appears that time has stopped for photon. But this relation is reflexive, so for an observer travelling with the photon it appears the universe has stopped everywhere.
...
10
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4answers
1k views
Travelling faster than the speed of light
Let's say I fire a bus through space at the speed of light. If I'm inside the bus (sitting on the back seat) and I run up the aisle of the bus will I in fact be traveling faster than the speed of ...
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9answers
3k views
Accelerating particles to speeds infinitesimally close to the speed of light?
I'm in a freshmen level physics class now, so I don't know much, but something I heard today intrigued me. My TA was talking about how at the research facility he worked at, they were able to ...
10
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3answers
863 views
“Speed” of Gravity and Speed of Light
Some threads here touching speed of gravity made me think about that. This lead to some questions.
The speed of gravity was not measured until today (at least there are no undebated papers to that ...
10
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4answers
356 views
The definition of an inertial reference frame in Einstein's relativity
I'm reading Sean Carroll's book on general relativity, and I have a question about the definition of an inertial reference frame. In the first chapter that's dedicated to special relativity, the ...
10
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3answers
911 views
What really cause light/photons to appear slower in media?
I know that if we solve the maxwell equation, we will end up with the phase velocity of light is related to the permeablity and the permitivity of the material. But this is not what I'm interested in, ...
10
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1answer
703 views
How realistic is the game “A slower speed of light”?
The game "A slower speed of light" from MIT claims to simulate effects of special relativity:
Visual effects of special relativity gradually become apparent to the
player, increasing the ...
10
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3answers
556 views
Can the speed of light become complex inside a metamaterial?
The speed of light in a material is defined as $c = \frac{1}{\sqrt{\epsilon \mu}}$. There are metamaterials with negative permittivity $\epsilon < 0$ and permeability $\mu < 0$ at the same time. ...
10
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1answer
240 views
How is it possible the speed of light is not constant?
I was reading this article recently, which summarizes a couple of new studies into the speed of light.
In one paper, Marcel Urban from the University of Paris-Sud, located in Orsay, France and his ...
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4answers
705 views
In superluminal phase velocities, what is it that is traveling faster than light?
I understand that information cannot be transmitted at a velocity greater than speed of light. I think of this in terms of the radio broadcast: the station sends out carrier frequencies $\omega_c$ but ...
9
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4answers
594 views
Why does the speed of light $c$ have the value it does?
Why does light have the speed it does? why is it not considerably faster or slower than it is? I can't imagine science, being what it is, not pursuing a rational scientific explanation for the speed ...
9
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4answers
369 views
How does $E=mc^2$ put an upper limit to velocity of a body?
How does $E=mc^2$ put a upper limit to velocity of a body? I have read some articles on speed of light and they just tell me that it is the maximum velocity that can be acquired by any particle. How ...
9
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6answers
3k views
Why can't light escape from a black hole?
Photons do not have mass (that's why they can move at speed of "light").
So, my question is how the gravity of black hole can stop light from escaping?
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3answers
939 views
Does a photon have a rest frame?
Quite a few of the questions given on this site mention a photon having a rest frame such as it having a zero mass in its rest frame. I find this contradictory since photons must travel at the seed of ...
9
votes
1answer
310 views
How is quantum mechanics compatible with the speed of light limit?
Consider a free electron in space. Let us suppose we measure its position to be at point A with a high degree of accuracy at time 0. If I recall my QM correctly, as time passes the wave function ...
8
votes
2answers
733 views
Does $E = mc^2$ apply to photons?
Photons are massless, but if $m = 0$ and $E = mc^2$ then $E = 0c^2 = 0$. This would say that photons have no energy, which is not true.
However, given the formula $E = ℎf$, a photon does have energy ...
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3answers
382 views
In a universe where the speed of light is infinite, are relativistic models and Newtonian models equivalent?
Take our universe. Observations are consistent with relativity, but not consistent with Newtonian mechanics. Assume that our current (relativistic) model of gravitation is correct. Now increase $c$ ...
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2answers
666 views
Does the speed of light vary in noninertial frames?
The speed of light is the same in all inertial frames.
Does it change from a non-inertial frame to another? Can it be zero?
If it is not constant in non-inertial frames, is it still bounded from ...
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11answers
7k views
Why does the mass of an object increase when its speed approaches that of light?
I'm reading Nano: The Essentials by T. Pradeep and I came upon this statement in the section explaining the basics of scanning electron microscopy.
However, the equation breaks down when the ...
7
votes
3answers
570 views
Why is a black hole black?
In general relativity (ignoring Hawking radiation), why is a black hole black? Why nothing, not even light, can escape from inside a black hole? To make the question simpler, say, why is a ...
7
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2answers
889 views
What happens if light/particles exceeded the speed of light for a particular medium
While the speed of light in vacuum is a universal constant (c), the speed at which light propagates in other materials/mediums may be less than c. This is obviously suggested by the fact that ...
7
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4answers
1k views
If a 1kg mass was accelerated close to the speed of light would it turn into a black hole?
I'm a big fan of the podcast Astronomy Cast and a while back I was listening to a Q&A episode they did. A listener sent in a question that I found fascinating and have been wondering about ever ...
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4answers
1k views
Why is the speed-of-light “the upper limit” rather than the speed of “particle type X”?
Basically, I can't stop wondering why light (the photon) is so special, compared to all the other particles known (and unknown) to modern day physics.
Could it be that there exists an upper limit on ...
7
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1answer
336 views
Can a black hole form due to Lorentz contraction? [duplicate]
Possible Duplicate:
If a 1kg mass was accelerated close to the speed of light would it turn into a black hole?
Imagine, a rod of length L is moving with velocity approaching the speed of ...
6
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4answers
794 views
Double light speed
Let's say we have 2 participles facing each other and traveling at speed of light
Let's say I'm sitting on #1 participle so in my point of view #2 participle's speed is c+c=2c, double light speed? ...
6
votes
13answers
965 views
The origin of the value of speed of light
Meaning, why is it the exact number that it is? Why not 2x10^8 /mps instead of 3? Does it have something to do with the mass, size or behavior of a photon? To be clear, I'm not asking "how we ...
6
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6answers
893 views
What are the most realistic ways of high speed space propulsion?
Liquid and solid chemical fuels in rockets are very expensive and inefficient. I have heard of solar sails but what are the most realistic space travel fuels that will be used in the future to get ...
6
votes
3answers
518 views
Special Relativity and $E = mc^2$
I read somewhere that $E=mc^2$ shows that if something was to travel faster than the speed of light then they would have infinite mass and would have used infinite energy.
How does the equation show ...
6
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3answers
536 views
At what speed does our universe expand?
Conceivably it expands with the speed of light. I do not know, but curious, if there is an answer. At what velocity, does our universe expand?
6
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1answer
519 views
Tachyon and Photons
Is there a particle called "tachyons" that can travel faster than light? If so, would Einstein's relativity be wrong? According to Einstein no particle can travel faster than light.
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3answers
337 views
Can something travel faster than light if it has always been travelling faster than light?
I know there are zillions of questions about faster than light travel, but please hear me out. According to special relativity, it is impossible to accelerate something to the speed of light. However, ...
6
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3answers
722 views
Alcubierre Drive - Clarification on relativistic effects
On the Wikipedia article on the Alcubierre drive, it says:
Since the ship is not moving within this bubble, but carried along as the region itself moves, conventional relativistic effects such as ...
6
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2answers
983 views
Why can't massless particle exceed speed of light?
Why massless particle can't exceed speed of light?
