**From:** John K Clark (*johnkclark@fastmail.fm*)

**Date:** Tue May 19 2009 - 10:09:23 MDT

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On Sun, 17 May 2009 "Matt Mahoney"

<matmahoney@yahoo.com> said:

*> The question is important to us because it means that
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*> regardless of any life prolonging mind or body enhancement,
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*> we will always have some doubt about our immortality even
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*> if we achieve it.
*

You’re treating this as if it was a question in pure mathematics and it

is not. The possibility of immortality boils down to the question: is

the universe capable of making an infinite number of calculations? A

calculation is not a mathematical abstraction, it is a physical process

that consumes energy, gives off heat, and produces entropy. Even if

calculations can go on for a infinite number of years that’s not the

same as an infinite number of calculations.

Landauer, Bennett and Merkle have shown that with reversible computing

the amount of energy needed to make a calculation can be made

arbitrarily small, but the only way to do it is by slowing down the

calculation. Fortunately 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. We won’t know if that’s good enough to allow

infinite computation until we know more about the basic laws of physics

and cosmology, and we won’t learn that from mathematics alone.

John K Clark

-- John K Clark johnkclark@fastmail.fm -- http://www.fastmail.fm - The professional email service

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