X-Message-Number: 3091
From:  (Nick Szabo)
Subject: CRYONICS: Determinism & reversibility
Date: Fri, 9 Sep 1994 01:35:55 -0700 (PDT)


There may be no practical difference between quantum mechanical 
processes that are truly random (as most physicists now believe) 
and ones that are driven by very chaotic deterministic processes.  
Even the most commonplace process of radioactive decay is at least so 
chaotic, that it is beyond the precision of our current instruments, 
and the statistical analysis capacity of our fastest computers, to 
tell it apart from a truly random process.  

A fundamental result in computation theory is that it is easy
to generate practically random sequences with a fully deterministic
process.  The Blum-Blum-Shub generator is one example of such
an algorithm.  The gap between the effort needed to generate
randomness, and the effort needed to reverse that process to
find the underlying determinism, grows quickly as amount of
generated information grows.  The amount of information in our brain
is a large indeed; if a significant nonredundant fraction 
of it undergoes computationally one way quantum change we're
dead beyond hope.  It doesn't effect the problem significantly to
assume faster computers; the difference quickly becomes so large that 
if every atom in the universe were a Cray, they still wouldn't be able 
to reverse the process.  The only way I could then be reanimated
is if we reached the hypothetical "Omega Point", and even then
I would only witness an infinitesimal fraction of the future.
I'm only infinitesimally satisfied with that.

Ralph Merkle has put forth a perceptive model called information 
theoretic death.  Along those lines, we might model death as a process 
of increasing randomization that at some point becomes computationally 
infeasible to reverse.  In the equilibrium or living state of the 
brain, the only computationally irreversible processes are channeled
into waste heat; structural processes are more or less at
an equilibrium of randomizing and ordering processes.
During ischemia the randomization quickly grows, until (at some 
point around currently defined medical death) the amount of
damage grows beyond the capacity of any in vivo ordering process.
By the time the corpse has rotted, restoring the brain back
to its original state has become computationally infeasible for any 
process.

The main question then becomes how reversible are the ischemia, 
perfusion, freezing, and vitrification processes undergone by neural 
tissue during suspension.   Ralph has started to tackle this with his 
excellent articles on the repair of the brain and "cryptanalysis" of 
freezing damage.  Much more knowledge of memory and its redundancy, as 
well as a much more detailed analysis of damage incurred in freezing
and vitrification, may be needed before we can make confident 
predictions about the reversibility of the suspension process.

Some parts of the dying process are known to be reversible with
a well observed probability.  For example, minutes of ischemia
at low temperatures.  I find Mike Darwin's research to be quite
valuable, as its goal is to physically demonstrate (a much
stronger result than theoretical proof) a perfusion/cooldown process 
that is reversible with high probability under a reasonable range of 
conditions.  Research on freezing and vitrification is also valuable, 
but the results are much more ambiguous.  For example, detailed STM pix 
of vitrified synaptic structure, with atom by atom accounting of the
damage, would be quite valuable, but would only allow improvement
in our indirect guesses of probability.  Atomic accounting is 
a kind of worst-case scenario that doesn't allow us to model memory 
redundancy.  It would be easy to have atomic displacements that in
themselves are computationally irreversible, but there exists
redundancy elsewhere in the brain, or even in other brains,
by which the original location can be inferred in a computationally 
feasible manner.  On the other hand, there may well be varieties of 
damage for which there is no computationally feasible redundancy.  
The area where brain research and information death theory may have 
the most impact, is to identify areas of low redundancy, difficult to
reverse damage, and to redesign suspension protocols to eliminate 
these forms of damage.  Assuming away irreversible damage is
very dangerous; that is precisely the kind of damage we should
be looking for in order to eliminate it.

Nick Szabo					

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