From: scerir (scerir@libero.it)
Date: Fri Feb 28 2003 - 07:45:41 MST
[fwd from 'undernetphysics', a yahoo group]
In the 28th Feb. 2003 issue of Science, there is an advance article
on a soon-to-be-published paper that theoretically shows the
possibility of having a "motion" without propulsion (i.e. not using
Newton's Third Law). Written by Jack Wisdom of MIT, the highly
mathematical and complicated paper reveals a motion similar to when
one is sitting on a swivel chair and by thrusting one's arm in
specific directions, one can make the chair turns. It is the same
effect that happens when a cat falls down and lands on its feet - by
twisting its torso.
This new paper deals with the same idea and involves with a curved 4D
spacetime. By stretching and retracting the "limbs" of a body, Wisdom
showed that one can "swim" through a curved spacetime. Interestingly
enough, and just like the swivel chair case where one can change
one's orientation but not spin, in this "swim" one can change one's
position but not the overall velocity.
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