Is relative speed of light constant?

Answer 1

The speed of light in a vacuum is absolute, unchangeable and can't be exceeded. The speed of light anywhere else depends on the material it moves through. c is indeed the c in e=mc2 - it is also the speed of light in vacuo. Any material has a speed of light associated with it, but that speed is not c, and that speed is neither a fundamental constant nor a universal speed limit. Photons are limited to that speed while in the material - that is what causes refraction. Material particles (those with mass) are not subject to the speed limit, any more than a rifle bullet is limited by the speed of sound. When a rifle bullet passes close to you, you hear a crack; this has the same origin as the sonic boom from an aircraft going supersonic. If a material particle that is travelling at close to c enters a material where the speed of light is less than the speed of the particle a shock wave is generated which is closely analagous to the sonic boom. There is no sound, just electromagnetic radiation, known as Cerenkov radiation. If you ever get a chance to observe a University reactor, almost all of which are water moderated, look down into the pool and admire the beautiful blue-green light surrounding the reactor core. That is Cerenkov radiation, caused by particles produced by the reactor going faster than the speed of light in water. As the particles bleed off energy into e-m radiation, they slow down. Once they are below the speed of light in water the Cerenkov production stops. It normally takes only a few feet.

Answer 2

The speed that light travels at depends of the medium in which it travels through. For instance, in a vacuum, light travels at approximately 3x108 meters/second. Mediums such as; air, water, and other materials have different indexes of refraction that cause the light to travel at slower speeds, however 3x108 meters/second is the fastest any light can travel.

Answer 3

That question cannot be answered with what we currently know about Nature. It is a fundamental tenet in special relativity, which has been thoroughly tested, and as a by product also in many derived things such as quantum field theory and general relativity, both of which also were verified experimentally.

It is an experimental fact that the speed of light is constant, and we base our theories on this, but why there has to be a constant of nature in the form of a speed is not known.

One could speculate of course, involve the anthropic principle etc., but that is no real answer.

It is an axiom of relativity and as such needs no explanation in relativity.

It is the speed predicted by Maxwell's equations using fundamental properties of electromagnetism. Why these properties are what they are is also unknown, but are determined by experiment.

Answer 4

The speed of light in a vacuum is, as far as we have been able to determine, the same everywhere (and there are good theoretical considerations for why this should be the case everywhere).

However, the speed of light is different in different materials.

Answer 5

The speed of light is the result of the electrostatic and magnetic properties of the medium

through which it's traveling. The speed changes only when those properties change.

Answer 6

The speed of light in a vacuum is constant.

Answer 7

Yes, depending on the medium it travels through

Answer 8

Yes the speed of light is the absolutely fastest speed in the universe according to modern physics. It is impossible to go faster than the speed of light.

Answer 9

No. The speed of light is always 299,792,458 meters/second

Answer 10

Yes it is constant. It never stops moving.