"Adam P. Goucher" <apgoucher@gmx.com> wrote:

The speed of light is actually constant.

Well, that clears that up. Hans Havermann <gladhobo@teksavvy.com> wrote:

Theoretical. There are two papers in Springer's 'The European Physical Journal D'. Here are the abstracts:

Thanks. I don't see anything in the first abstract that Feynman didn't say decades ago. This tiny variation in the time light takes to travel a fixed path is more commonly expressed as Heisenberg uncertainty in the length of that path. Thomas Knight <tk@csail.mit.edu> wrote:

Perhaps the Casimir effect can be used to detect a shift, given its change in the population of virtual particles in the gap.

Maybe. Intuitively, this quantum effect should be much larger than the general relativistic effect due to the negative mass-energy in the gap, and both effects should cause light to go faster. However, since faster light could cause causality violations, there's probably some reason this won't work. Dan Asimov <dasimov@earthlink.net>

Naturally, since the speed of light is constant by definition, it must be the length of a meter that potentially can vary.

And what does *that* mean? It varies relative to what?