X-Message-Number: 31715
Date: Wed, 03 Jun 2009 01:25:49 -0700
From: Mike Perry <>
Subject: Virtual Time Travel (Retrodiction)
References: <>

The idea of retrodicting history and in some way using this 
information to either reassemble deceased individuals from 
constituents (atoms, say) or replicate them in some other suitable 
way, goes back at least to the 19th-century philosopher Fedorov. A 
crucial question is whether the past can be so retrodicted. The 
evidence to me seems meager at best that this will prove possible. 
(You would have to, for instance, recover the detailed brain 
structure of persons whose brains have long since decomposed.) 
Granted, there could be properties of reality that will permit this 
with suitable advanced technology, but again it seems doubtful. 
Reality could be deterministic (every effect has a cause) without 
there necessarily being a path back, informationally, to any desired 
point in the past. If the past cannot be retrodicted we may ask if 
there could still be a means of resurrecting the unpreserved dead. It 
seems clear to me that the answer is "yes" because, for instance, 
finite patterns of information could be recreated by pure guesswork, 
as a last resort. A scenario I've laid out for resurrections and more 
generally dealing with what I call information-deficient cases (as 
might occur in cryonics), is at 
http://www.universalimmortalism.org/resurrection.htm .

The issue was raised about whether the entire visible universe (a 
"Hubble volume") could be exactly duplicated. Basically a Hubble 
volume is a finite construct like a brain, only much bigger, so the 
answer in both cases, with suitable assumptions about quantum 
discreteness, is yes. Physicist Max Tegmark has this to say 
(see  http://space.mit.edu/home/tegmark/multiverse.pdf ): "A crude 
estimate suggests that the closest identical copy of you is about 
10^(10^29) m [meters] away. About 10^(10^91) m away, there should be 
a sphere of radius 100 light-years identical to the one centered 
here, so all perceptions that we have during the next century will be 
identical to those of our counterparts over there. About 10^(10^115) 
m away, there should be an entire Hubble volume identical to ours." 
(To say that something is a certain distance away does not mean you 
could necessarily travel there, even in principle, yet it would still exist.)


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