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Wayne McCoy
2007-Jan-19, 11:05 PM
Does anyone know of anything in current theory that suggests why the velocity of light in vacuo is finite and of the value 3X10^8 m/s? What I'm looking for here is something that impedes photons traversing spacetime. Is spacetime the source of this impedance, perhaps interaction with the virtual particles created in the Higgs field or constraint to follow the Planck-level structure of spacetime (e.g., Wheeler's foam)?

Ken G
2007-Jan-19, 11:37 PM
I think the problem with thinking in terms of impedence is, you're going to need an infinite impedence to get an infinite speed down to c. It may be true that light "wants" to move at infinite speed, and something prevents it from doing that, but it would be hard to use the language of impedence. Still, maybe there's a deep way to think of light as "trying" to be infinitely fast but is "held up" by virtual interactions of some kind, that seems like it might be a useful insight. Alternatively, maybe you couldn't have light at all without those interactions-- the interactions that "slow" light might be necessary in order to get any energy into the light in the first place.

Wayne McCoy
2007-Jan-20, 01:09 AM
@KenG
Yes, I suppose the use of the word "impedance" is loaded -- we think of electrical impedance in a circuit. I was thinking more generally, in terms of "something that impedes, or interferes with." I was curious to know if any recent theory has treated this. Thanks for your answer.

Jeff Root
2007-Jan-20, 01:20 AM
Hello, Wayne!

I think that Ken was interpreting the term "impedence" the way
you intended.

Consider this: How fast would a water wave move if it were not
being impeded by the water?

-- Jeff, in Minneapolis

Amber Robot
2007-Jan-20, 01:26 AM
Consider this: How fast would a water wave move if it were not
being impeded by the water?

Sounds like a zen riddle :p

Sam5
2007-Jan-20, 01:55 AM
Sounds like a zen riddle :p

Lol, sounds like the old Shelly Berman joke about the one hand clapping.

Wayne McCoy
2007-Jan-20, 03:39 AM
Consider this: How fast would a water wave move if it were not
being impeded by the water?

Without the water there would be no wave. But the analogy seems strained, since there is no medium in which light waves (Michelson-Morley experiment).

trinitree88
2007-Jan-20, 02:52 PM
Without the water there would be no wave. But the analogy seems strained, since there is no medium in which light waves (Michelson-Morley experiment).

Wayne. Actually, that's not true. The apparent negative result of the MM experiment has four separate, physically valid interpretations (Isaac Asimov,"On Physics"..circa 1970) only one of them was that the "luminiferous ether" did not exist. It has been the most widely accepted in view of its' simplicity, but that does not make it explicity true. One of the others was that the ether exists, but that it has properties such that a MM experiment cannot detect it..i.e. it causes the things we numerically see in Special Rel.
Light in fact traverses the neutrino sea, in which we all live, and neutrinos can interact via the neutral current which couples to all the particles in the Standard Model. The cross-sections for low energy neutrinos are being determined at the Sudbury Neutrino Observatory as we speak. Whether that will produce a "something" that impedes light (as in tired light) as you suspect, time will tell. At the present time effects which are produced by accelerating an object inertially,SR, or producing a gravitational acceleration through the presence of mass ,GR, are always accompanied simultaneously by local reference frame neutrino sea gradient changes, since you cannot remove the "sea" from your experiment. Whether that will quantitatively yield measurable results will be tricky to tease out of the data as neutrinos cross-sections in general are prohibitively low....but they're not zero.Pete.

Wayne McCoy
2007-Jan-20, 03:28 PM
@trinittree88

Thanks! That's the kind of answer I was seeking. I'm aware of the various aether theories -- at least that they are out there -- but I haven't seem anything that explicitly treats the transmission of photons

Ken G
2007-Jan-20, 07:55 PM
Furthermore, the interaction would need to be frequency independent, or the Planck spectrum of the CMB would not be preserved during "tiring". How likely do you think that would be, if you think it is mediated by neutral current interactions?

Wayne McCoy
2007-Jan-20, 09:34 PM
Furthermore, the interaction would need to be frequency independent, or the Planck spectrum of the CMB would not be preserved during "tiring". How likely do you think that would be, if you think it is mediated by neutral current interactions?

I think too that that there would have to be something "uniform" about the interaction, else there would be variations in the velocity, and the velocity might vary with distance -- cumulative effect of some sort. But the velocity is seen to be constant and independent of distance as far as experiment can divulge. Moreover, polarization is preserved, and presumably phase.

I'm wondering if such an interaction, if it exists, might be the source of the "drag" on bodies being accelerated to light velocity in SR, in the sense that the mass increases and more energy is required to overcome the "drag." Conceptually, I think of something analogous to friction, without the heating.

Or, who knows, maybe it's just all them wiggly little strings getting knotted up.:)