From: hal@finney.org
Date: Thu Jun 10 1999 - 15:51:11 MDT
I seem to recall reading an analysis of the (original)
Alcubierre warp drive in terms of causality. Can you get the
classical special relativity causality paradoxes which normally
flow from FTL travel? There is some discussion of this at
http://www.physics.purdue.edu/~hinson/ftl/html/FTL_part4.html#sec:stmanipulation
When we were talking about wormholes and causality, one of the ideas
floating around was that virtual particles could enter a closed timelike
loop and end up amplifying themselves each pass around, which took
place outside of time. The effect was an instantaneous, spontaneously
created spear of energy which would collapse the wormhole. I wonder
if a similar phenomenon wouldn't occur with any sort of FTL travel that
violates causality.
Wormholes have some properties in common with the Alcubierre warp,
namely the need for negative energy, and the possibility of FTL travel
and associated paradoxes.
More recently Anders referred us to http://xxx.lanl.gov/abs/gr-qc/9903061
which seems to prove that wormholes can't exist.
One of the papers referenced by Van Den Broeck is available at
http://www.ioppublishing.com/PEL/article/cq14011l1/full/:
The expectation value of the stress - energy tensor of a free
conformally invariant scalar field is computed in a two-dimensional
reduction of the Alcubierre `warp-drive' spacetime. Unless the
spacetime is in the Hartle - Hawking state at an appropriate
temperature, the stress - energy diverges on past and future event
horizons which form when the apparent velocity of the spaceship
exceeds the speed of light. The likelihood of the spacetime being in
this state, whether due to natural evolution or the application of
technology, is briefly discussed.
This sounds a bit similar to the wormhole collapse phenomenon, although
the author indicates that it might perhaps be avoided with some care.
Hal
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