From: steppe@ccwf.cc.utexas.edu (Top Changwatchai)
Newsgroups: rec.puzzles
Subject: Re: Virtual reality puzzle
Date: 21 Aug 92 10:09:52 GMT
Organization: The University of Texas at Austin, Austin TX

In article <1992Aug19.145636.26007@cs.cornell.edu> karr@cs.cornell.edu (David Karr) writes:
>In article <9882@uqcspe.cs.uq.oz.au> warwick@cs.uq.oz.au writes:
>>karr@cs.cornell.edu (David Karr) writes:
>>
>>>In article <9881@uqcspe.cs.uq.oz.au> warwick@cs.uq.oz.au writes:
>>>>Trivial:  Open up the VR machine in your Real/VR homes, and examine EVERY
>>>>  component.  The VR machine cannot possibly store the details of its own
>>>>  construction (where would it store them?).
>>
>>>Nonsense....
>>
>>Nonsense it's nonsense...
>
>All right, maybe "nonsense" was a little strong, but the argument is still
>fundamentally and fatally flawed.
>
>...
>
>>As I said originally, this all relies on you ability to tell the difference
>>between a mock-up VR machine and the real thing... maybe that's the hard part.
>
>Yes, well, this is a good point.  I would expect that the simulated
>dust motes that settled inside the simulated VR machine are not in the
>same locations as in the real one.  But without being able to go back
>and look at the real machine to compare, how are you ever going to be
>able to tell?  Even if you'd had the foresight to take detailed notes
>and photographs before starting the simulation, if you're still in the
>simulation these will be fake anyway and can be altered to suit.  Even
>if you think you see a discrepancy between what you see and what you
>remember, how much can you trust your memory to that level of
>detail--in real life?
>

As to whether you could distinguish between simulation and reality in
practical terms, I'd say it depended largely on how "perfect" the VR
simulator was.  After all, if it's real enough that you can't immediately
tell the difference between simulation and reality, then I doubt it's going
to slip up in some detail ("Aha!  That violated the 2nd law of
thermodynamics!  Ergo, I'm in the simulation.").  On the other hand, the
first thing the user is going to want to know is how to get out of the
simulator and know it; the company is probably obliged to provide some
sort of verification (i.e., only the "orc module" will be loaded, and not
the "everyday life module").

>
>In fact, there's a theorem of computability that says there is a
>computer that can describe itself.  Specifically, there is a Turing
>machine M that, given any input, prints out a complete description of
>M (itself) on its tape.  You can easily extend the proof of this
>result to have the machine print out a text that describes exactly
>what a Turing machine is in general, and how you should interpret the
>description of M.
>
>This result is considered non-intuitive, so you may be excused for
>having skepticism, but it's true nevertheless.
>

I've followed the argument for the creation of the universal Turing machine
(and seen an "example" of one in Penrose's "The Emperor's New Mind").
However, there seems to be a difference between the theoretical and practical
mappings between the VR machine and a perfect Turing machine:  efficiency.

If the machine could simulate reality (and not just a strictly limited
orc adventure) in real time, then why doesn't the company just develop
one that would predict the future?  They'd make a fortune.

(Of course, now that I think about it, the VR machine could use all kinds of
dirty tricks.  Maybe slow down your responses to give it computation time.
Inject fun stuff into your head so you won't care to verify the reality of
the simulation.)

All in all though, practical considerations aside, I concur:  you would have
no way of knowing whether it's a simulation or not.  But why worry?  How do
you know you're not in a simulation right now?  (Your real memories, of
course, have been suppressed for the duration of the simulation.)

>------
>
>This VR thread reminds me of an SF story I read once--unfortunately I
>forget the author and title--about a man who is leaving his house on a
>rainy day, suddenly remembers something he forgot back in the house,
>and when he goes in he looks out a window and sees sunny skies behind
>the house.  Meanwhile, back at the control center for the simulation
>the man is in, there is hell to pay for whoever was so careless as to
>allow this discrepancy to show up.
>
>Anyone remember the author and title?
>
>-- David Karr (karr@cs.cornell.edu)

Don't know what story you're referring to, but it reminds me of a mildly
interesting short story I read once, titled "The Electric Ant" I believe.  In
the story, "electric ants" are robots that are programmed to think they are
human, and in fact they hold human jobs.  Anyway, the protagonist one day
discovers that he is an electric ant (quite by accident) and decides to
experiment:  he opens himself up and pokes holes in his "reality ticker tape"
(yes, this was a pretty cheesy story).  When the mutilated section was
scanned, he would experience phenomena corresponding to the holes (say, a
flock of geese in his living room).

Anyway, he decides to commit suicide.  Although his friend tries to stop him,
he succeeds in cutting his reality tape.  As he's winding down, the point
of view of the story switches over to his friend, who finds herself slowly
disappearing, much to her surprise and dismay.  She is simply part of the
fellow's program, though she thinks that she thinks and acts under her own
free will and all.

Hmm.

Top
---
  "If that there King was to wake," added Tweedledum, "you'd go out--bang!--
just like a candle!" - Lewis Carroll
-- 
steppe@ccwf.cc.utexas.edu
"I'm gonna live forever or die trying."