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Re: fHuman vs. natural influences on the environment



In article <JMC.96Aug17081450@Steam.stanford.edu> jmc@Steam.stanford.edu (John McCarthy) writes:

   In article <lkn2zuunvo.fsf@sandy.ast.cam.ac.uk> steinn@sandy.ast.cam.ac.uk (Steinn Sigurdsson) writes:

    In article <2bnLmKAOsMFyEweQ@wandana.demon.co.uk> Jim Barr <JimBarr@wandana.demon.co.uk> writes:

       Several years ago, at a symposium for astrophysicists held in London, an
       experiment was carried out.  All the delegates were asked to calculate
       how much energy it would take to bring one stationary electron from a
       point in deep space ( but near a KNOWN stellar object) and bring it to
       rest on the surface of the earth.

       They would allow for mass and movement of all *major* solar objects but
       not asteroids or deep space objects apart from the one mentioned above.

       They were all *capable* of  doing the sums and several of them did so.
       The unamazing fact was that the *answers* that these scientists came up
       with differed by as much as 13 orders of magnitude.

    I don't believe you. Please provide a citation.

   I don't understand.  

   It would seem to me that the energy required to move the electron
   depends entirely on the electric potential difference between the
   point in space and the surface of the earth.  I would expect that to
   be entirely unknown.  I doubt that the potential differences are known
   even within the solar system and may not even be constant over time.
   It seems to me from what I have read that a lot is known about the
   potential difference between the ionosphere and the earth's surface,
   but I don't know if it is constant geographically or in time.

Exactly. Although the gravitational potential difference
also needs to be accounted for in principle (and could in
practice dominate the total energy requirement).

The paragraph on the movement of solar objects is a complete
red herring, the rest makes very little sense. The only conceivable
situation where the energy requirement is so uncertain is, say,
if the electron needs to be removed from the polar cap of a
pulsar. Otherwise the anecdote is rubbish, and actively
misleading. Hence I'd like to know which symposium this
occured at - if only so I can go yell at whoever
was off by 10^12 1/2 ;-)






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