Cosmic uncertainty: Is the speed of light really constant?

New Scientist ^ | 03/01/2017 | Stuart Clark

[SeekAndFind]

The speed of light in a vacuum is the ultimate cosmic speed limit. Just getting close to it causes problems: the weird distortions of Einstein’s relativity kick in, so time slows down, lengths go up, masses balloon and everything you thought was fixed changes. Only things that have no mass in the first place can reach light speed – photons of light being the classic example. Absolutely nothing can exceed this cosmic max.

We have known about the special nature of light speed since an experiment by US physicists Albert Michelson and Edward Morley in the 1880s. They set two beams of light racing off, one parallel and one at right angles to the direction of Earth’s rotation, assuming the different relative motions would mean the light beams would travel at different speeds – only to find the speed was always the same.

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Light’s constant, finite speed is a brake on our ambitions of interstellar colonisation. Our galaxy is 100,000 light years across, and it is more than four years’ light travelling time even to Proxima Centauri, the closest star to the sun and home, possibly, to a habitable planet rather like Earth.

Then again, if the speed of light were infinite, massless particles and the information they carry would move from A to B instantaneously, cause would sit on top of effect and everything would happen at once.

[Ultra Sonic 007]

Ping of interest

[shockwaver]

There must not be too much scattering, photon/photon or otherwise. The spectrum lines are pretty sharp, even from the most distant sources.