Yes, really. You and me and everything in the universe is travelling at the speed of light, through SpaceTime. Light is only peculiar in that the temporal component of its velocity is zilch. 

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''I'm sorry to disagree. Considering a certain frame of reference, only light and light-like things may move at just that speed... it's a matter of inertial frames of reference... we can measure, therefore we don't move at the speed of light. At that speed it's not possible to define an inertial frame of reference, which means we cannot measure things by ourselves. On the other hand, the temporal component of something (if my physics hold, it's been a long time) would be (minus) 1 over gamma (where gamma is the square root of 1 over (1 minus beta squared), beta being the speed in terms of the speed of light). But that doesn't necessarily hold true when you make the limit where beta goes to 1... Limits are tricky when you approach speed 1. OTOH, our events-line through spacetime never reaches tangent 1, because that would imply exerting an infitite amount of momentum, which nothing can... Light, precisely, defines the frontier between bradions and taquions... Only light and some other bosons (and matbe some neutrinos, although experimental data suggest at least two of the three types do have mass, indeed)...''

Considered in terms of relativistic, classical, space-time events, when light enters a dense (but transparent, at that wavelength) medium its 4-d velocity arrow gets rotated a bit towards the time axis, hence it appears to slow down, because some of its spacial velocity has gone away. Nothing ever gets accellerated, it just has its velocity arrow rotated.

And you thought software was hard.

''Software is hard...''

''What's happening when light enters a medium is that photons are absorbed (destroyed) and reemitted (created) by the atoms in the medium. The excitation and desexcitation is pretty fast, but not instantaneous. The delay created by Avogadro's Numbers of atoms in a material (or by that order) does effectively slow down the front wave of a beam, thus creating the illusion the beam has moved more slowly. Actually it's not the same beam anymore... Maybe spinorial theory explains things that way... fortunately, there are more clearer points of view for the same phenomena... Nowadays, Quantum Electrodynamics (QED) explains light and its interaction with electrons (matter). Relativity has a lot to say about it, but some things are pretty well settled, I think.''

Yep, all that's true too. All that QED absorption and re-emission and all the virtual particles and re-normalization and stuff is the mechanism, as far as anyone can tell. But Einsteinian relativity, which we were discussing above, has not truck with all that quantum shenanigans.

'':-) I think it's not productive to apply a model where it's not designed to work... and electromagnetic phenomena aren't relativistic (in the sense to be meaningful to apply General Relativity to its full)... BTW, the photon is a relativistic particle (sort of) and so is the electron... but as I said before, I think it's twisting the tensor too far when you try to apply a model far from its natural media (relativity: big mass densities, big speeds)... Simple is beauty...''

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Well, I can ''walk'' '''faster''' than the speed of light.  That is, if the light is travelling through a Bose Einstein condensate.  The new (February 2000) record for the slowest light speed is 1 mile per hour.  See http://www.aip.org/enews/physnews/2000/split/pnu472-1.htm for details.  (See the Physics News Update site: http://www.aip.org/physnews/update/ for many more interesting abstracts.  Some of this stuff makes science fiction seem tame...)

''Looks cool... :) Problem is: you can walk '''here''' faster than light in that condensate (apparent group speed, only, btw)... How fast can you walk in that condensate, though? <eg> :o) Thanks for the URIs''

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CategoryPhysics