Re: More Open Universe (FTL travel and GR)
Tue, 3 Feb 1998 17:38:32 -0500

Someone wrote:

> Relativity doesn't say it's impossible
> to move faster than light, it just says you can't send matter, energy or
> information between two points faster, and an expanding universe does not do
> this.

General relativity (GR) does forbid faster-than-light (FTL) travel through
However, GR places no restriction on the speed at which space can inflate.
If you are 50 light years from point B and you set out at .99 the speed of
light towards
that point B, you will get there in less than 50 years due to the length
predicted by GR. However to a (essentially) stationary observer on Earth 50
years would
pass between the time you set out for point B and the time you actually reached
point B.

Quantum tunneling would appear to violate the GR prediction that information
can not travel
at FTL speeds through space-time. However, you can not determine the state of
the new
quantum state until you observe it. Since you can not travel at FTL speeds you
can not
reach the object that experienced quantum tunneling and learn the information
in a manner
that would violate GR.

The whole affair is nonintuitive and if you are confused thats a strong sign
that you
understand it! :)

Doug Bailey