From: John K Clark (johnkc@well.com)
Date: Wed Sep 04 1996 - 11:11:56 MDT
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>John K Clark
>Dyson showed that if the universe is open there would always
>be a time when life could exist, but that's not immortality
>because it would not be possible for the universe to
>perform an infinite number of calculations
>Robin Hanson
>Dyson showed that a computer could go through an infinite
>number of compute cycles starting with a finite energy store.
>But various such computers would find it increasingly
>expensive to communicate with each other, as the distance
>between them increased.
>Anders Sandberg
>But the big question is if this prevents memory growth. [...]
>Would the energy needed to communicate with my remote memory
>banks become prohibitive?
Landauer, Bennett and Merkle have shown that with reversible computing the
amount of energy needed to make a calculation can be made arbitrarily small
by slowing down the calculation a little. Even a small reduction in speed can
help a lot in energy saving, the power dissipation (per unit of time) falls
as the SQUARE of the speed, and at the Omega point things will naturally speed
up because at the Big Crunch the parts of your computer will keep getting
closer together so it takes less time to send a message from one part to
another. More recently in the June 28 1996 issue of Science, Landauer shows
(in a interesting but non practical way) how you can also communicate and not
just compute information with an arbitrarily small amount of energy if you
are willing to slow things down.
We'll never run out of energy to perform a calculation if the universe
reverses it's expansion in a non symmetrical way and we have a big crunch.
We will have not a huge amount of usable lots of energy, we will have an
infinite amount. Tipler's idea is to trade energy for subjective time,
we have infinite energy so we have infinite time.
In an open universe you only have a finite amount of energy to work with,
so you'll want to slow things way down, but other problems that Landauer did
not consider will force you to slow things even more, and use more energy
too. The components of your brain keep getting more distant so that's going
to keep slowing things way down. Also, in order to establish reliable
communication it's going to take more and more photons of light to send one
bit of information. It won't be easy for one part of a brain to hit it's
target a billion trillion light years away, not much chance if you only send
one photon. Also, each photon will be strongly and increasingly redshifted,
to compensate the sender must keep shorting the wavelength of the photons he
uses, this takes more energy and you only have a finite amount of it.
>Anders Sandberg
>As I understand it, a sufficiently slowly growing being
>would never have any problems with redshifts *inside* itself.
I don't see why that would be so.
John K Clark johnkc@well.com
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