starship-design: Many Questions

[Steve VanDevender <stevev@efn.org>]

kyle writes:
 > WARNING! Off-topic (for now)
 > 
 > Greetings:
 > 
 > I come with questions:
 > 
 > 1. What causes antigravity? Theoretically in the big bang?

I'm no expert in inflationary big bang cosmology.  The inflationary
models postulate that spacetime expanded at a very high rate during the
very early moments of the universe.  In essence the radius of the
universe expanded faster than the speed of light for some brief amount
of time.

 > 2. Is neutronium that was spoken of the degenerate matter in neutron
 > stars?

Neutronium is basically just a huge clump of neutrons.  Neutron stars
are formed when a collapsing stellar core reaches a pressure high enough
to cause protons and electrons to combine into neutrons.

Besides being incredibly dense, neutronium would be really hard to work,
particularly since even small chunks would probably tend to just turn
into spherical blobs from their own gravity.  I think that you also have
to have some minimum pressure to keep it stable, or the neutrons will
just beta-decay back into protons and electrons again.

 > 3. Why does light speed up in casimir cavities?

Presumably as a result of a change in electromagnetic properties of the
vacuum.  c = 1/sqrt(m0 * e0), where m0 is the magnetic permittivity of
the vacuum and e0 the electric permittivity.

 > 4. What part of FTL causes causality violations?

This I can speak to more authoritatively.  A slower-than-light path
through spacetime always appears to move forward in time (at different
rates) for all observers, and events connected by particles travelling
at or below the speed of light always have the same time order but with
different time intervals between events measured by different observers.
Faster-than-light paths can appear to move forward in time for some
observers and backward in time for others depending on their relative
velocity to the events in question, and events connected by
faster-than-light paths therefore don't have the same time order for all
observers.

 > 5. What is Tipler's infinite rotating cylinder? A man made black hole?

Frank Tipler showed that the general-relativistic solution for the
spacetime curvature around an infinitely long, massive rotating cylinder
contained paths that allowed travel in time as well as space.  While
this is theoretically interesting, there are some massive practical
problems (to understate it) with building such a cylinder; even if you
didn't have to make it infinitely long, one dense enough to work would
be incredibly difficult to restrain against axial collapse into a normal
black hole.

Nick Herbert's _Faster than Light_ discusses a lot of the
general-relativistic approaches to faster-than-light travel.
Unfortunately the proposals so far are all seemingly impossible to
construct in our universe.

 > 6. What would happen to space surrounded by negative energy?

I'll leave this for someone else :-)

 > Kyle Mcallister