Re: opposite of relativistic time contraction

On 2008-03-16, Ben Crowell <crowell07@xxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
Mmm...I would consider diffraction to be a fundamental physical
limitation, not a minor engineering problem. If the laser is
at rest with respect to the galaxy, then it has to operate over
distances of light-years.

You want to accelerate a 10^17 kg black hole at 100g over distances of
at least a couple of light-years? Ouch. The project then needs at
least 10^37 J of energy available.


In any case, there's another issue that seems more fundamental,
which is that 10^29 W converts via E=mc2 to 10^12 kg/s, which is
enough to double the mass of our black hole in hours.

Oh, if you need more than that, then don't feed the beam into the
hole: just let the hole's gravity bend it, say 150 degrees or so. As
a bonus, you get nearly double the momentum transfer. Of course the
redshift will be a problem in any event since the gamma factor will go
past 200.

On the plus side, the diffraction problem isn't as bad as you think:
an on-site collimator can direct the laser to the correct location
near the hole.


Good point. Well, the exhaust velocity can be a small fraction of c
-- you want it to be a small fraction of c in order to get a decent
thrust-to-power ratio.

Absolutely not: the mass/payload ratio is exponential in
delta-V/exhaust and for 100g acceleration over 2 light years the
delta-V is at least 6c. If converting mass directly into energy at
arbitrary rates is a problem, then the whole project is doomed.


Maybe the magnet is on the end of a 10 km superconducting cable
trailing behind the thrust module.

Heh, the cable is subjected to a tension of 10^20 N. I think ordinary
matter is out of the question.


- Tim
.

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