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. Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=13362