X-Message-Number: 4640 From: Ralph Merkle <> Subject: Response to Donaldson's post Date: Mon, 17 Jul 1995 19:59:05 PDT Thomas Donaldson recently said (CryoNet Message #4631) that I have concluded that "...we need not worry about our suspension technology." I trust most readers will recognize that this is, shall we say, an inaccurate representation of my views. Various other statements by Thomas about what I said are also significantly biased. Thomas also said (CryoNet Message #4629): "I have not yet examined Ralph's posting on WWW. In that sense, I'm not qualified to say anything; however...." Further comment on this statement would appear superfluous :-) The article to which Thomas is objecting is "Cryonics, cryptography, and maximum likelihood estimation," which can be found on the web at: http://merkle.com/merkleDir/cryptoCryo.html The basic thrust of this article is that certain cryptanalytic methods used to determine the (initially unknown) wiring in World War II rotor machines could be applied to the problem of determining neuronal structure when there is incomplete information (caused, for example, by a poor suspension) about that structure. Several years ago, in an article discussing the first publication of "Molecular repair of the brain" Donaldson said "A robot of molecular size astounds and amazes. But exactly what computations is it supposed to *do*? Without answers to that question, no one can even decide whether the approach is practical." (Cryonics, Vol. 11, No. 1, January 1990, page 31). More recently, in reference to "The Technical Feasibility of Cryonics" published in Medical Hypotheses, Donaldson said "Unfortunately his argument was then and remains utterly fallacious on this central point of the computer power required. Furthermore, depending on the kind of "analysis" we ask of a data base, there is quite literally no amount of computer time required to do the analysis." (*It's not at all so easy,* Cryonics 3rd Quarter 1994, page 37). Naturally, I assumed Thomas would be pleased with more detailed descriptions of the algorithms that could be used :-) Alas, this has not proven to be the case :-( Those interested in my views might wish to read my cryonics page at http://merkle.com/merkleDir/cryo.html Those interested in articles by Tadd Hogg and colleagues on phase transitions in constraint satisfaction search can see ftp://ftp.parc.xerox.com/pub/dynamics/constraints.html To quote from the cited URL: "Many studies of constraint satisfaction problems have demonstrated, both empirically and theoretically, that easily computed structural parameters of these problems can predict, on average, how hard the problems are to solve by a variety of search methods. A major result of this work is that hard instances of NP-complete problems are concentrated near an abrupt transition between under- and overconstrained problems. This transition is analogous to phase transitions seen in some physical systems." In the current context, this implies that the computational costs of determining the healthy state are likely to be tractable unless the damage to the neuronal tissue has been sufficient to render such a determination almost infeasible. Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=4640