[extropy-chat] Relativity drive: the end of wings and wheels?
Eliezer S. Yudkowsky
sentience at pobox.com
Sat Sep 9 18:44:54 UTC 2006
Hal Finney wrote:
> Keith's example may not have worked, but Dirk Bruere explained a few
> months ago that a reactionless drive is inconsistent with conservation
> of energy. This is true even if the drive uses power to produce thrust.
> Suppose constant power leads to constant thrust, as the principle of
> relativity would require. Constant power implies that total energy used
> will be proportional to time; but constant acceleration makes velocity
> proportional to time, and kinetic energy is proportional to v^2, which
> means it is proportional to time squared. Any time you have input energy
> proportional to time while output energy is proportional to time squared,
> you will go over unity after enough time.
"Shawyer cautions that the calculations only work for static thrusts.
‘You can’t beat the laws of physics. If it is used to accelerate, the Q
value drops. It is best used to lift a body and oppose a force, for
instance to counteract gravity. It cannot be used to accelerate further.’"
Sounds like this violates the equivalence principle in General
Relativity. Staying put against gravity = accelerating in free space.
Eliezer S. Yudkowsky http://singinst.org/
Research Fellow, Singularity Institute for Artificial Intelligence
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