X-Message-Number: 13362
Date: Sun, 05 Mar 2000 08:17:39 -0800
From: "Ralph C. Merkle" <>
Subject: Feasibility of cryonics

My own views on the feasibility of cryonics have been expressed in "The 
Molecular
Repair of the Brain," available at http://www.merkle.com/cryo/techFeas.html.

To quote one relevant passage from that source:

   The damage caused by extracellular ice formation depends largely on the 
fraction
   of the initial liquid volume that is converted to ice[6, 57]. (The 
initial liquid
   volume might include a significant amount of cryoprotectant as well as 
water).
   When the fraction of the liquid volume converted to ice is small, damage 
is often
   reversible even by current techniques. In many cases, conversion of 
significantly
   more than 40% of the liquid volume to ice is damaging[70, page 134; 71]. The
   brain is more resistant to such injury: conversion of up to 60% of the 
liquid
   volume in the brain to ice is associated with recovery of neuronal 
function[58, 62,
   66, 82]. Storey and Storey said "If the cell volume falls below a 
critical minimum,
   then the bilayer of phospholipids in the membrane becomes so greatly 
compressed
   that its structure breaks down. Membrane transport functions cannot be 
maintained,
   and breaks in the membrane spill cell contents and provide a gate for ice to
   propagate into the cell. Most freeze-tolerant animals reach the critical 
minimum
   cell volume when about 65 percent of total body water is sequestered as 
ice."[57].

   Appropriate treatment with cryoprotectants (in particular glycerol) 
prior to freezing
   will keep 40% or more of the liquid volume from being converted to ice 
even at
   liquid nitrogen temperatures.


The following observations are relevant:

1)  Current Alcor suspension protocols call for the introduction of 
sufficient glycerol
      to reduce ice formation to substantially below 40% of the initial 
liquid volume.

2)  Functional survival is generally a more stringent criterion than 
information
      theoretic survival.

Based on these (and other) observations, and based on the near certainty 
that a mature
nanotechnology will be able to reverse any secondary structural damage, it 
seems likely
that present protocols, when carried out under favorable conditions, can 
produce a
satisfactory outcome -- assuming that the non-technical issues (e.g., 
maintaining people
in suspension until appropriate medical technology can be developed and used)
can be dealt with successfully.

However, as current suspensions are not always carried out under favorable 
conditions,
it is necessary to consider the ultimate limits of survival.  The primary 
purpose of such
considerations is to determine at what point we should abandon hope and 
reallocate
our efforts in other directions.  The use of cryptanalytic methods should 
permit recovery
of information relevant to long term memory and personality when conditions are
significantly unfavorable, suggesting that suspensions should be continued 
despite
such circumstances.  A discussion of the application of cryptanalytic methods
to cryonics is at http://www.merkle.com/cryo/cryptoCryo.html.  A discussion
of more general issues relevant to the technical feasibility of cryonics, 
including
some discussion of mechanisms of injury that might be encountered in cryonic
suspensions, is available at http://www.merkle.com/cryo/techFeas.html.

While I am sympathetic with the desire for absolute knowledge and utter 
certainty,
and improving our state of knowledge is certainly a desirable goal, it is 
not the only
desirable goal.  Organizational growth, favorable changes in the social and 
legal
systems that we operate under, and many other objectives are also worth 
substantial
effort.  As organizational growth provides additional resources which can 
be applied
to all the other areas of concern, and as it can also save lives, it is 
particularly worthy
of our attention.

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