X-Message-Number: 15054
Date: Wed, 29 Nov 2000 23:28:52 -0700
From: Mike Perry <>
Subject: More on Turing Emulations

Robert Ettinger, #15045, says

>A Turing machine (finite but 
>unlimited sequential digital computer) is classical in its construction and 
>behavior, even though it can calculate quantum mechanics. Since its 
>capabilities are finite, it cannot generate a full set of Many Worlds future 
>histories of any system, let alone an emulated person.

A "full set" of future histories might require infinite time. However, from
an appropriate starting point, bounded (finite) in energy and spatial
extent, the TM could patiently enumerate the possible outcomes for
successively increasing but always finite times. Over finite time there will
only be finitely many possible different states for such a system. So over
infinite time our TM would generate all the infinite possibilities. It
would, of course, be grossly inefficient since the number of possibilities
it would have to consider would grow exponentially with the time step.

> ... It [the TM again] can only, at best, generate 
>successive internal computer states corresponding to successive most-probable 
>quantum states of the emulated system.

Again (I posted on this yesterday) the TM could change its states
probabilistically and thus pick the less probable states sometimes. (Indeed,
I've seen a chess machine that did this very thing. If you tried to play the
same game twice by repeating your moves it would vary its moves thus
producing a different game.) Such a device, then, should be able to model
quantum state changes with the expected frequencies so that emulating a
complex system like a human being is not ruled out. Note that this idea is a
different one from the many-worlds emulation where all possible future
histories are emulated (though again with great inefficiency). In the
probabilistic case, only one timeline is considered, which seems far more
reasonable from a practical standpoint. But it is also fascinating that the
quantum computer could overturn this judgment, so that maybe some form of
many-worlds emulation is what will actually be done.

Mike Perry

Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=15054