X-Message-Number: 19746
From: 
Date: Sat, 10 Aug 2002 12:31:49 EDT
Subject: probabilities

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George Smith and Steve Harris commented today on estimates of probability of 
success in reviving cryonics patients. 

Essentially, Mr. Smith seemed to take the position (shared by some of the 
major figures in mathematics) that it is not meaningful to talk about the 
"probability" of a particular event. It will happen or it won't. 
"Probability" only applies to sequences or collections of events, an average 
ratio of "successes" to "trials." Some have pointed out, for example, that 
one can just as meaningfully speak of the "probability" of heads for a coin 
about to be tossed, or for a coin already tossed but not yet inspected. The 
latter in one sense is history, with no "probability" about it--but from the 
point of view of the observer there is no difference.  (Mr. Smith does of 
course make some other good points.)

Dr. Harris mentioned the Drake equation, assuming that an event depends on 
the success of each of several independent requirements, each with its own 
probability, the final result found by multiplication. But, besides making 
some other good points, he noted that the assumptions are questionable and 
the invidual estimates widely variable.

My own viewpoint is different, and set forth at length on our web site. I 
have no delusion that it will be persuasive to many, but I challenge anyone 
to refute it. The upshot is that there is in general no such thing as "the" 
probability of an event, although we have this impression from common 
experience with overly simple situations such as games of chance or 
statistical mechanics. Instead, to calculate a probability, one must first 
define a sequence of experiments and the criteria of  "success" in an 
individual outcome, and USUALLY there will be many possibilities in real-life 
problems. A full study would have to deal with second-order probabilities 
(probabilities of probabilities), but that is another story and usually an 
informal choice is good enough or the only one available.

Bottom line--odds on for success.

Robert Ettinger
Cryonics Institute
Immortalist Society
www.cryonics.org

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