From: Hal Finney (hal@finney.org)
Date: Mon Mar 10 2003 - 17:11:32 MST
Scerir writes:
> Indefinite Information Processing in Ever-expanding Universes
> http://arxiv.org/abs/gr-qc/0302076
> Authors: John D. Barrow, Sigbjorn Hervik
> Comments: 6 pages
> We show that generic anisotropic universes arbitrarily close to the open
> Friedmann universe allow information processing to continue into the
> infinite future if there is no cosmological constant or stable
> gravitationally repulsive stress, and the spatial topology is non-compact.
> An infinite amount of information can be processed by ``civilisations'' who
> harness the temperature gradients created by gravitational tidal energy.
> These gradients are driven by the gravitational waves that sustain the
> expansion shear and three-curvature anisotropy.
I see three problems with this as a practical solution to our future
information processing needs.
The first is that current cosmological evidence suggests that there is
a cosmological constant, possibly even an increasing one, which would
mean that this method won't work, since it requires a zero CC.
The second is that although the paper describes how to extract energy from
gravitational waves "forever", it's not clear whether it is possible to
actually build a processing machine that can grow in size indefinitely.
Unless the size of the machine can increase without bounds, the number
of possible states that it has is limited, and so eventually it will be
forced to repeat calculations it has already done. In effect life would
be marching in place and would no longer be progressing, a philosophically
unsatisfying ending.
The third is that Tipler sketched a proof in his book The Physics of
Immortality that infinite computing was impossible in an open universe,
and I didn't see this paper explicitly mentioning that proof or explaining
why his proof didn't apply to this case.
Hal
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