Re: SCI: slow light

Anders Sandberg (
19 Feb 1999 11:34:02 +0100 writes:

> However...that leads to a question. If light is "slowest" in a Bose-Einestein
> Condesate...and "fastest" in a there anything "less" than a
> vacumn? It is possible to slow light it even theoretically
> possible to speed light up?
> No clue here...a vacumn is a vacumn right?
> Right?

Depends on what kind of vacuum it is :-)

Actually, I seem to recall that the speed of light is different in the vacuum between the plates in the Casimir force experiment, where the vacuum is actually given a slightly negative energy. This is from the realtivity FAQ:

The Casimir effect is a very small, but measurable force which exerts between two uncharged conducting plates when they are very close together. It is due to vacuum energy (see the Physics FAQ article on the Casimir Effect). A surprising calculation by Scharnhorst suggests that photons travelling across the gap between the plates in the Casimir effect must go faster than c by a very very small amount (at best 1 part in 1024 for a 1 nanometre gap.) It has been suggested that in certain cosmological situations, (such as in the vicinity of cosmic strings if they exist) the effect could be much more significant. However, further theoretical investigations have shown that once again there is no possibility of FTL communication using this effect.


K. Scharnhorst, Physics Letters B236, 354 (1990) S. Ben-Menahem, Physics Letters B250, 133 (1990) Andrew Gould (Princeton, Inst. Advanced Study). IASSNS-AST-90-25 Barton & Scharnhorst, J Phys A26, 2037 (1993)

Anders Sandberg                                      Towards Ascension!                  
GCS/M/S/O d++ -p+ c++++ !l u+ e++ m++ s+/+ n--- h+/* f+ g+ w++ t+ r+ !y