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Hal's Extropians Digest      Thu, 18 Jun 1992       Volume 92 : Issue   0009

    Selected messages from the Extropians list.  To join, send to:
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    Hal Finney
    Extropians Digest Moderator

Today's Topics:
		    QM vs Relativity (6 messages)

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Date: Wed, 17 Jun 92 17:58:40 EDT
From: [...]
To: Extropians@gnu.ai.mit.edu
Subject: Newcombs paradox

I may be butchering this badly, but I seem to recall reading somewhere
that quantum mechanics and relativity are in conflict. This has something
to do with somebody named Bell.

Here's a thought experiment. Suppose one has two boxes, each
containing a cat, isolated in such a way that they will both be shot
if a certain quantum effect happens at a certain time. The qunatum
effect occurs with a 50-50 probability.

We start the experiment. The cats are either killed or not. The
bystanders cannot know without looking in the boxes. Two bystanders,
Axel and Krishna each take a box without looking inside. They then
travel to far distant places.

Krishna then looks into her box. Her cat is dead (alive). She
immediately knows that Axel's cat is dead (alive). Because of quantum
uncertainty, information can travel faster than the speed of light!

Has anybody heard this before? Is this a serious problem or not?

                                  [...]

P.S. Many of these environmental arguments seem, to me, to go like
this.

I'd like ecological problems not to exist. The experts conflict.
Therefore I'll pick the ones that agree with my desired view. QED,
Greens are mistaken.

Very seldom do I hear arguments about assessing the consequences if
one view or the other is wrong. What's happens if environmental damage
beyond a certain point is a disaster and we do not address it first?
It seems one could construct a strong Pascal's wager-type argument for
addressing environmental problems early. (Note, I'm am not saying that
one shoul ignore all other values, such as allowing individuals the
maximal freedom to run their lives as they seem fit.)

P.P.S. Has anybody here heard of Karl Popper? Does anybody know
whether there was any mutual influence between Popper and Hayek?

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Date: Wed, 17 Jun 92 15:44:48 -0700
From: uunet!auburn.ee.washington.edu!davisd
To: Extropians@gnu.ai.mit.edu
Subject: Dead cats


Krishna then looks into her box. Her cat is dead (alive). She
immediately knows that Axel's cat is dead (alive). Because of quantum
uncertainty, information can travel faster than the speed of light!

****************

Sounds to me like Krishna carried the information in her own mind by
knowing the relationship between the two cats.

Buy Buy -- Dan Davis

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Date: Wed, 17 Jun 92 20:04:22 EDT
From: Mark Edward Desilets <uunet!skylab.src.umd.edu!desilets>
To: Extropians@gnu.ai.mit.edu
Subject: Re: Newcombs paradox

 [ dead cats and etc deleted....]
>
> Has anybody heard this before? Is this a serious problem or not?
>
>                                   [...]
>

   No, it is not a problem.  The only knowledge you have is that
   t seconds ago you both were given dead/alive cats.  This is
   isomorphic (if you excuse the loose use of the word) to the
   knowledge of the outcome of the (observable) experiment.  This
   information travels with you at your less-than-light speed.
   It is no different from carrying a letter from your wife and opening
   it when you get to you destination.  As you read the letter, you
   and your wife both know what she wrote.  Does this seem a
   paradox?  If the asymmetry bothers you both of you can carry letters
   and open them a predetermined delta_t from your parting time.

                                                        Mark

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Date: Wed, 17 Jun 92 16:09:25 PDT
From: uunet!ghsvax!hal (Hal Finney)
To: Extropians@gnu.ai.mit.edu
Subject: QM vs Relativity

> I may be butchering this badly, but I seem to recall reading somewhere
> that quantum mechanics and relativity are in conflict. This has something
> to do with somebody named Bell.

There are a couple of misconceptions in this message.  There are some
senses in which QM and Relativity conflict, but it is more subtle than
is being suggested.

Consider this case of what might appear to be "faster than light"
communication that doesn't involve QM.  I have two boxes, and I hide a
ball in one of them.  Two people each take a box, not knowing which
has the ball, and travel light-years apart.  They then each open their
box.  One of them learns that he has the ball, and thereby learns
instantly that the other person doesn't have it.  Evidentally the
information that the other person doesn't have the ball travelled
faster than the speed of light!

This is clearly false, showing that you have to be careful about how
you picture information flow in these situations.

When we add QM to the example, though, the situation becomes trickier.
Instead of putting a ball into one box, I let the wave function for an
electron spread out so that it has an equal chance of going into
either box, then seal the boxes.  Now, in QM terms, it's not strictly
correct to say that one box has the electron and one does not.
Instead, each box has half the electron's wave function.

This can be proven because the boxes can in principle be brought back
together, opened, and the two "half electrons" allowed to merge in
such a way that certain interference phenomena result.  If the
electron had been firmly located in one box, such quantum interference
could not occur.

So, we are forced to say that the electron really is in a
superposition of states of being in each of the two boxes.  Now, when
you separate the boxes by light-years and open them, one box is found
to hold the electron.  Under conventional interpretations of QM, it is
only at that very moment that the electron wave function "collapsed",
and the electron ended up in that box.  Up until that moment the
electron really was in some sense in both boxes.

The wave function collapse would actually be triggered by opening just
one of the boxes.  Evidentally by opening a box here, one can cause an
instantaneous change in a box light-years away.  The universe thus
appears to allow non-local actions, in violation of basic concepts of
relativity.

(Note, though, that this type of non-local action can not be used to
send a message faster than light.  When you open your box there may be
a sense in which my box changes state, but no measurements I can make
on my box will tell me when you've opened yours.  All I can do is open
my box and see if I have an electron, and there will be a 50-50 chance
of that no matter what you do.)

IMO, this whole analysis, although quite conventional, can be better
understood as revealing the limitations of the usual interpretations
of "wave function collapse" than showing that the universe is
nonlocal.  That is why other interpretations of QM are gaining in
popularity.  The July Scientific American has an article which
mentions some of the newer interpretations.

Hal Finney
ghsvax!hal@uunet.uu.net				...!uunet!ghsvax!hal
Permission is granted to freely reproduce this message.

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Date: Wed, 17 Jun 92 20:38:21 EDT
From: uunet!gnu.ai.mit.edu!rjc
To: Extropians@gnu.ai.mit.edu
Subject: Re: QM vs Relativity

> So, we are forced to say that the electron really is in a
> superposition of states of being in each of the two boxes.  Now, when
> you separate the boxes by light-years and open them, one box is found
> to hold the electron.  Under conventional interpretations of QM, it is
> only at that very moment that the electron wave function "collapsed",
> and the electron ended up in that box.  Up until that moment the
> electron really was in some sense in both boxes.
>
> The wave function collapse would actually be triggered by opening just
> one of the boxes.  Evidentally by opening a box here, one can cause an
> instantaneous change in a box light-years away.  The universe thus
> appears to allow non-local actions, in violation of basic concepts of
> relativity.
>

    This is one of the things that bugs me about QM. What constitutes
an observation?  Does it take a sentient being to collapse a wavefunction?
What if an AI "opened the box"? What if the box itself was an intelligent
nanite?
    I personally believe that QM is only a very good approximation of
of the underlying complexity of the microscopic world. The Many Worlds
and Copenhagen interpretation of QM both introduce some rather awkward
circumstances into the notion of 'objective reality'. The New Age
seems to like this, and has taken to manipulating QM into supporting
their notions of thought amnd reality. (e.g. they claim that
since observation collapses the wavefunction, thought controls
reality)

-- Email to rjc@gnu.ai.mit.edu -- CUT HERE -- PGP Public Key --
begin 644 rjc_gnu.pub
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M(>!I?7LPJOW8N$720'LO@.N$G]5BX!N[,!#+%(G6BWJ6(,>RT5*7$,&G_+Q;
.28^$>OV+38WF93P% !,O

end

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Date: 17 Jun 92 23:09:30 EDT
From: Michael Clive Price <uunet!CompuServe.COM!100034.3077>
To: Extropians@gnu.ai.mit.edu
Subject: Re: QM vs Relativity

>    This is one of the things that bugs me about QM. What constitutes
>    an observation?  Does it take a sentient being to collapse a
>    wavefunction?  What if an AI "opened the box"? What if the box
>    itself was an intelligent nanite?
Very good questions.
>    The Many Worlds and Copenhagen interpretation of QM both
>    introduce some rather awkward circumstances into the notion of
>    'objective reality'.
Oh?  Many-worlds a la Everett was devised explicitly to avoid all the
paradoxes of wavefunction collapse entailed in Copenhagenism.  If you
throw out wave-function collapse (and get many-worlds) you get rid of all
need to define observers and have self-contradictory definitions of
'objective reality'.  Reality becomes the identified with the universal
wavefunction.

The many-worlds interpretation is uncomfortable for many people because
it conflicts with their (single-threaded) view of reality.  But then the
idea of that the world is round did as well, but we accept it because it
is the only self-consistent model of the world.  Many-worlds says that
the only self-consistent model of the universe is one that contains many
worlds.

All else is quackery and Voodoo and ultimately dissolves into the
absurdities of thought controlling reality and other 'New Age' rot.

Mike Price

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End of Hal's Extropians Digest Volume 92 Issue #0009
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