X-Message-Number: 9300
From: Ettinger <>
Date: Mon, 16 Mar 1998 21:23:13 EST
Subject: Display and Scratch

Here is another possible problem with emulation of a physical system by a
digital computer. I don't recall having seen it mentioned before.

In the prevailing view, if I understand it correctly, a physical system
changes over time by taking on successive new quantum states. This just
happens; there is nothing "in between" states. Every part and aspect of the
system makes its contribution to the total reality; there is nothing lacking
and nothing extra.

In a digital computer, trying to emulate the physical system, the situation is
fundamentally different--even aside from the fact that successive quantum
states of the emulated system are represented by successive COLLECTIONS of
classical states of the Turing computer.

First, there are two main categories of numbers, which we might call "display"
numbers and "scratch" numbers. The display numbers are those specifying values
for the parameters of the quantum states of the emulated system. The scratch
numbers are the results of intermediate calculations on "scratch paper" that
are needed by the program in order to find the next display numbers. Scratch
numbers correspond to nothing in the emulated system. (The program itself also
corresponds to nothing in the emulated system--not even to the laws of
physics, except in a very restricted sense.)

Second, the display numbers themselves are of two kinds. Since I am talking
about a Turing type machine, only one new display number at a time can be
entered--and in fact, in the case of the ur-tape, usually only a portion of a
number. So at a particular moment (from our point of view), in general, we
have some display numbers for the old quantum state parameters and some for
the new. The whole collection of display numbers then represents a straddle of
quantum states. A straddle corresponds to nothing in the emulated system.  

O.K., perhaps the programmer can label those numbers and moments he wants to
be "on the record," eliminating straddles and scratch. One can also claim it
is permissible for an emulation to have something extra, as long as it lacks
nothing--in other words, a suitable partial isomorphism. But is it really that
easy?

At this point we have to look at the rationale for believing that a "real"
system can be constituted of mere symbols or numbers and their changes and
relationships. The argument is that while a symbol by itself means little or
nothing, a complex network of symbols, with well defined and orderly
relationships, can be as "real" a system as the one being emulated, or as
realistic as the one being studied. After all, our own brains seem to work
with nothing but electromagnetic and chemical signals that are mostly just
symbols at the cognitive level (leaving aside the self circuit, hormones,
muscle impulses etc.), but we can use learned patterns to make inferences
about the outside world. The proof of the pudding is that we also act upon the
outside world, by moving our bodies etc., and the interaction holds up to
analysis.

This is fairly persuasive, and (digressing) it also leads into another
area--rejection of the notion that you can't possibly tell if you are in an
emulation, or at least a doctored emulation. If your brain is not subjected to
internal interference, but someone seeks to fool it through virtual reality
manipulations, you retain the potential ability to see through the deception,
i.e. to detect anomalies in the alleged outside world. For example, a person
emulated in a classical Turing computer (if that is indeed possible) could
conduct experiments that would cast light on his situation. Deutsch has made
similar remarks.

…..I have forty eleven other threads to pursue and modify, and previous
remarks to clarify and follow up…..and higher priorities. Have to quit--and
unless my will power fails, I don't plan to return to this discussion any time
soon. You're welcome.

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

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