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Re: starship-design: Re: Aliens

kyle writes:
 > Steve VanDevender wrote:
 > > kyle writes:
 > >  > Why doesn't ZPE deplete? Your guess is as good as mine.
 > > Who says it doesn't?  I've never seen even the physicists who propose
 > > extracting energy from it claim that zero-point energy won't be depleted
 > > by extraction.  
 > I don't think it does since there have been no witnessed disasters
 > accomanying ZPE. I think that if you use ZPE, somewhere, ZPE is
 > replenished. After all, why doesn't gravity deplete?

Kyle, I would hope after all this time you'd start learning how to
build logically convincing arguments.

It may be that you can't extract zero-point energy, or that phenomena
we're seeing that don't have other explanations could be zero-point
energy extraction disasters, or that extracting zero-point energy
changes the vacuum.  Without any evidence, it's hard to say which,
although I tend towards the last alternative.

If zero-point energy is extractable, and it doesn't produce disastrous
effects, then the most likely explanation is that it's like draining
from a very deep reservoir.  There's a certain finite amount of energy
tied up in the vacuum, and extracting it is simply converting it to
mass/energy.  Unrestricted extraction of zero-point energy could result
in both changes to the vacuum on a large scale and the increase of the
mass density of the universe, possibly even with dangerous effects if
done on a large scale.

Why doesn't gravity deplete?  Well, why don't electric fields deplete
either?  Because they're conservative potential fields (conservative
meaning that they observe conservation laws, not that they're
philosophically stodgy).  That means that moving through a closed loop
in such a field produces no net change in energy.  As it turns out,
gravitational potential energy from gravitationally bound objects does
actually leak away over time in gravity waves, albeit extremely slowly.
But this is actually just conversion of the potential energy in the
separation of the masses into propagating spacetime disturbances; once
(over a truly astronomical time scale) the masses come together and
coalesce, they still exhibit the gravitational field resulting from
their combined masses.  If you're dubious, look up the astrophysical
observations of some massive closely-coupled binary systems that show a
gradual decrease in period resulting from the gravitational radiation.

 > Where are the deficit neutrinos? What are they?

I've never heard of them.  As with the zero-point experiments, where are
your references?

 > What is gravity? I know the knee-jerk response is: its produced by mass.
 > But what IS it?

Curvature (change of the geometric properties) of spacetime.  See
Misner, Thorne, and Wheeler's _Gravitation_.

 > Why does light accelerate in a casimir cavity?

Which experiment showed this?  So far I've only heard of the Casimir
effect as a theoretical possibility.