CryoNet #31712 - #31715

CryoNet - Wed 3 Jun 2009

    #31712: Pizer's time travel [Daniel Crevier]
    #31713: Virtual Boy Will Talk and Play with You [Mathew Sullivan]
    #31714: Re: CryoNet #31708 - #31711 [2Arcturus]
    #31715: Virtual Time Travel (Retrodiction) [Mike Perry]

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Message #31712
From: Daniel Crevier <[email protected]>
References: <[email protected]>
Subject: Pizer's time travel
Date: Tue, 02 Jun 2009 11:55:07 -0400

Traveling back in time by running a backwards simulation from the present is 
a good idea, but it suffers from a major weakness: you can't go back more 
than a short period in time without running into the same problems you get 
when trying to predict the weather. The differential equations describing 
the world can be integrated both backwards and forward, but a small error 
accumulates at each time step in both cases. This is due to the so-called 
butterfly effect, whereby small causes can have large consequences. More 
specifically, tiny errors in the  evaluation of the initial state of the 
system get amplified over time, until the calculated state doesn't have any 
relation with reality. In order to preserve accuracy over time, a perfect 
knowledge of the initial state would be needed, which is impossible because 
of quantum uncertainty (you can't know both a particle's speed and position 
with perfect accuracy). This is a fundamental limitation of nature, and a 
galaxy-wide computer wouldn't do you any good.

For this reason, earlier proponents of the idea, like Mike Perry in Forever 
for All, if I understand him correctly, recommend a backwards simulation 
that would be constrained to conform to known historical facts (which would 
be used as 'boundary conditions' in mathematical jargon). Whatever facts the 
simulation provides that are not part of the historical record would then 
constitute at best educated guesses on what really happened, as there is an 
infinite number of historical novels that can be written and fit what is 
known of history. The simulation would just extract the most likely ones.

Of course the task would be easier for historical characters for which many 
facts are know : Napoleon, about whom there are mountains of bibliographies, 
could be reconstructed with a lot less guesswork than an anonymous grunt in 
his army.

So if you want to be brought back, leave as many traces behind as you can. 
And get your loved ones to do the same.

Daniel Crevier, Ph.D.

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Message #31713
Date: Tue, 2 Jun 2009 18:37:29 -0400
Subject: Virtual Boy Will Talk and Play with You
From: Mathew Sullivan <[email protected]>

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Be sure to watch the video in the link!

Mathew

Virtual Boy Will Talk and Play with You
http://www.livescience.com/technology/etc/090602-virtual-boy-will-talk-and-play-with-you.html

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Message #31714
References: <[email protected]>
Date: Tue, 2 Jun 2009 16:35:11 -0700 (PDT)
From: 2Arcturus <[email protected]>
Subject: Re: CryoNet #31708 - #31711

--0-366505548-1243985711=:28383

>>>Message #31708
Date: Mon, 1 Jun 2009 11:07:30 -0400
Subject: Time observation in the past, sci fi book recommendation
From: Rudi Hoffman <[email protected]>
Anyone else read this?

Rudi,
That's one of my favorites. Really great perspective and vision. 
Note that, in that book, the people in the past are brought back to life without actually travelling into the past or changing it.



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Message #31715
Date: Wed, 03 Jun 2009 01:25:49 -0700
From: Mike Perry <[email protected]>
Subject: Virtual Time Travel (Retrodiction)
References: <[email protected]>

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.)

MikeP

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