X-Message-Number: 13331
From: 
Date: Tue, 29 Feb 2000 11:39:13 EST
Subject: information recovery

Eugene Leitl writes, in part:
-----------
>Now for the bad part: the cryptography analogy is unfortunately
>totally bogus. The damage description in

>   http://www.merkle.com/cryo/cryptoCryo.html 

>bears only tenuous connection to reality, and the assumption that
>there is no information loss in the system because "The laws of
>physics are reversible, and so in principle recovery of complete
>information about the original state should be feasible" is not valid.

[snip]

>if the information is still Out There, but is meanwhile spread over a
>lightcone with (say) 100 lightyears radius, and is still receding
>fast, at the quite formidable speed of light                
------------
We all talk past each other on occasion, instead of really paying attention 
to what the other fellow is saying. 

I have recently reminded readers that information recovery is NOT limited to 
calculating reverse trajectories or inferring past quantum states from first 
principles, and we are NOT reduced to following fugitive photons or anything 
like that.

As just one example, suppose you wanted to know the genome of someone who has 
been burned to a crisp in a fire. I don't think Mr. Leitl or anyone else 
would call that impossible. All you need do (not easy, just relatively easy 
at some future time) is to collect DNA samples from as many living relatives 
as possible. Knowing the relationships, one could then infer, to a high 
degree of accuracy, the genome of the crisp. Or you might even be able to 
find a hair or skin flake left behind somewhere by the crisp. A whole lot of 
other information would also be relevant.

Suppose you wanted to know whether George Washington had false teeth. You 
don't have to back-track the atoms in his remains, or even open his grave. 
All you have to do is read a little; it is a matter of historical record. 

In other words, to repeat, there are countless anchor points in accessible 
history-known (or relatively easily knowable) facts that enormously reduce 
the dimensions of the inference problem. 

Of course Mr. Leitl is entirely correct in saying that additional information 
would be more valuable than additional speculation. But the speculation still 
has its place and use.

Additionally, I would suggest that the cryptography analogy, however 
imperfect, does have some validity. Among other things, it forcefully reminds 
us that destroying or even concealing information is not easy. Cryptographers 
DELIBERATELY TRY to conceal information, yet even so are often unsuccessful. 
Nature is not deliberately trying to conceal anything. 

Robert Ettinger
Cryonics Institute
Immortalist Society
http://www.cryonics.org

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