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Subject: SPACE Digest V11 #36

SPACE Digest                                      Volume 11 : Issue 36

Today's Topics:
               Re: Spacewarps?
                 Spacewarps?
     Can one obtain the Voyager "Sounds of Earth" album?
Re: Easy come, easy go (was Re: Spacecraft drives and fuel efficiency)
----------------------------------------------------------------------

Date: 12 Feb 90 05:18:26 GMT
From: cs.utexas.edu!jarvis.csri.toronto.edu!helios.physics.utoronto.ca!physics.utoronto.ca![e-mail]  (Christopher Neufeld)
Subject: Re: Spacewarps?

In article <[e-mail]> [e-mail] (Tim Maroney) writes:
>In article <[e-mail]>
>[e-mail] (Christopher Neufeld) writes:
>>   In principle there would be no energy requirements to keep such a
>>warp-generating object contained and spinning. Containment does not require
>>energy. Spinning would happen in vacuum, and the dissipation would be
>>slight. Actually, there might be some energy loss due to gravitational or
>>Hawking radiation, depending on the geometry. I leave it to specialists in
>>the field to estimate those.
>
>Why do you say containment wouldn't require energy?  The treatments
>I've seen indicated that degenerate matter or neutronium would be
>required, and these are not gravitationally stable at these sizes
>(unless we're talking about planet-sized machines -- again, at this
>technology level, controlling tons of antimatter would probably not be
>a problem).  The centrifugal force from spinning at near c would tear
>the thing apart in nanoseconds unless some sort of opposing force were
>used to contain it.
>
   Containment doesn't require energy. A force is not energy. Energy
results when a force acts across a distance (the integral of the scalar
product of F with dx). Consider: a compressed gas canister contains the
gas, but it doesn't need batteries to do it, and it won't fail after some
well-defined period of time because it has run out of energy.
   Remember, if it consumes energy, it must be radiating energy, or raising
the potential energy of the combined system. So, if your spinning torus is
held together with the thirtieth century equivalent of elastic bands and
chewing gum, they wouldn't consume energy. If it's held together by
"tractor fields", well, then the elements generating your fields might
themselves be dissipative, but that is a separate problem from the matter
of containment.

>--
>Tim Maroney, Mac Software Consultant, sun!hoptoad!tim, [e-mail]
>
>"I believe that bigfeet from outer space are stealing ships
>from the Bermuda triangle area.  Prove me wrong."
>    -- Bob Dainauski, [e-mail], on sci.skeptic


--
 Christopher Neufeld....Just a graduate student  |
 [e-mail]              | "Vulcan has no moon."
 [e-mail]                    | "I'm not surprised!"
 "Don't edit reality for the sake of simplicity" |

------------------------------

Date: 11 Feb 90 17:24:18 GMT
From: cs.utexas.edu!jarvis.csri.toronto.edu!helios.physics.utoronto.ca!physics.utoronto.ca![e-mail]  (Christopher Neufeld)
Subject: Spacewarps?

In article <[e-mail]> [e-mail] writes:
>
>> Unfortunately, the speculative "gate" approaches such as the Kerr
>> metric warp are even worse.  Has anyone done any estimates on the
>> energy needed to keep a Kerr warp contained and spinning?
>
>What is a "Kerr metric warp", who is Kerr, and what sort of physics
>  does this involve?  Is this merely some science fiction conjecture
>  or is it based on reputable theory?
>
   Taken from the technical appendix to _The McAndrew Chronicles_ by
Charles Sheffield:
   Roy Kerr is a physicist. He formulated a relativistic description of a
rotating body while working out of the University of Texas at Austin in
1963. This particular description deals with energy storage and extraction
in rotating black holes, and not with space warps. See one of the Phys.
Rev. Letters from September, 1963, titled "Gravitational field of a
spinning mass as an example of algebraically special metrics."

   The physics involved in the space warp theories are all classical (ie.
not quantum mechanical) general relativity.
   The theory is reputable, as many aspects of the theory have been
confirmed by experimentation or observation of celestial bodies.
   One problem with general relativity is that, contrary to popular belief,
the equations actually require causality violation for some geometries,
even some which are not "black holes", so that the surface escape velocity
is below the speed of light. Some of these solutions appear to be robust,
so they would probably not be affected by small perturbations from the
symmetry which made the solutions tractable. In other words, though some of
the solutions require perfect spherical or cylindrical symmetry, and so may
be disrupted by any energy density (such as a prospective time traveler)
approaching them, other seem to be able to transmit matter along non-causal
paths.
   I'd provide you with some real references, but one of my tutorial
students took my copy of Robert L. Forward's _Future Magic_ in which the
references are listed. If anybody out there has the book, they might look
it up for those people who are interested.
   Anyway, there are all sorts of strange solutions which come out of
general relativity. I believe the Kerr warp mentioned in the previous
posting is the result of a toroidal mass rotating about its symmetry axis.

>How do you estimate how much energy it takes to induce one?
>
   Well, weigh the starting materials for the torus, spin it up, weigh it
again, take the difference, multiply by the square of the speed of light,
and convert to the units of your choice (troy bushels or whatever :-) ).
Anyway, the mass difference should come out of the equations naturally as
the general relativistic form of the rotational energy of the body.
   In principle there would be no energy requirements to keep such a
warp-generating object contained and spinning. Containment does not require
energy. Spinning would happen in vacuum, and the dissipation would be
slight. Actually, there might be some energy loss due to gravitational or
Hawking radiation, depending on the geometry. I leave it to specialists in
the field to estimate those.

>Scott


--
 Christopher Neufeld....Just a graduate student  |
 [e-mail]              | "Vulcan has no moon."
 [e-mail]                    | "I'm not surprised!"
 "Don't edit reality for the sake of simplicity" |

------------------------------

Date: 12 Feb 90 00:15:03 GMT
From: zaphod.mps.ohio-state.edu!samsung!aplcen!haven!ncifcrf!nlm-mcs![e-mail]  (Michael D'Alessandro)
Subject: Can one obtain the Voyager "Sounds of Earth" album?

I know that this was discussed back in the summer when Voyager encountered
Neptune, but I didn't follow that discussion then...

I have a friend who would like a copy of the Voyager "Sounds of Earth" album
that was produced by Carl Sagan and placed on both Voyager spacecraft.  Is
this commercially available?
--
Michael D'Alessandro M.D.
The National Library of Medicine
Lister Hill National Center for Biomedical Communications
Educational Technology Branch            Internet:  [e-mail]

------------------------------

Date: 12 Feb 90 06:12:57 GMT
From: zaphod.mps.ohio-state.edu!samsung!cs.utexas.edu!jarvis.csri.toronto.edu!helios.physics.utoronto.ca!physics.utoronto.ca![e-mail]  (Christopher Neufeld)
Subject: Re: Easy come, easy go (was Re: Spacecraft drives and fuel efficiency)

In article <[e-mail]> [e-mail] (Frank C. Paterra) writes:
>In article <[e-mail]> [e-mail] (Steve Nuchia) writes:
>   In article <[e-mail]> [e-mail] (H
>Keith Henson) writes:
>>>energy to laser light.  Lasers will levitate against 1g, and as someone
>>>(Henry?) recently said, a year at one gee is the speed of light.
>>>(How to stop is left as an exercise)  Keith Henson
>>Robert Forward's solution to this excersize (_Flight_of_the_Dragonfly_)
>>was to release the main reflector at turnover and use the reflected
>>(and refocused) beam to deccelerate the ship using a smaller secondary
>>reflector.  The former main reflector is of course accelerated further
>>on the outbound axis.
>
>Assuming you guys have solved all the problems of accelerating
>the ship, how about when you reach the half way point, pointing
>the solar sail at the destination star and using it to decelerate
>the ship?
>
   No. In Robert L. Forward's book the ship doesn't ride on natural
sunlight. A solar power station inside Mercury's orbit powers a
multi-gigawatt laser array (numbers, anybody? My copy of the book is in
Montreal) which is focused by a Fresnel lens near the orbit of Jupiter.
This lens focuses the beam back down to a few hundred kilometres wide at
the ship, even a few light-years away. The photon flux at the ship is very
much higher than that available from starlight at that point. Natural
starlight at the destination wouldn't even dent the speed of the incoming
spacecraft, which was some tenths of the speed of light.

>>--
>>Steve Nuchia          South Coast Computing Services      [phone]
>
>Frank Paterra
>[e-mail]


--
 Christopher Neufeld....Just a graduate student  |
 [e-mail]              | "Vulcan has no moon."
 [e-mail]                    | "I'm not surprised!"
 "Don't edit reality for the sake of simplicity" |

------------------------------

End of SPACE Digest V11 #36
*******************