Re: Quantum Weirdness

From: Eliezer S. Yudkowsky (
Date: Sat Dec 11 2004 - 23:30:49 MST

Jeff Medina wrote:
> Dani,
> A photon, not being an observer, has no point of view, and thus the
> 'problem' of relativistic spacetime corrections for a photon's
> reference class is ill-founded and meaningless.
> Harvey,
> Whoa. I currently find MW the most plausible interpretation of quantum
> physics, and I don't subscribe to *ANY* of the drivel you just
> attributed to MW theorists. Messianic rapture? Were you mauled by a
> gang of MWI-spouting mafia at some point or something? Perhaps you're
> not clear on what the MWI is, or the arguments for it?

I second this sentiment. Harvey, I think you must have encountered the
wrong version of many-worlds. I also find Everett-Wheeler the best
quantum theory, and not because of any emotional consequences it might
or might not have. As Tegmark points out, once you think the universe
to be spatially infinite, the existence of quantum worlds is quite
irrelevant/unnecessary philosphically; the spatial infinity provides as
many worlds as one could wish, or fear. I find MW the best theory
because of its pure, mathematical elegance. In fact, I confess myself
utterly incapable of comprehending quantum physics without it.

The so-called "Copenhagen interpretation" contains hidden informal
parameters by refusing to specify what constitutes an "observation" or
how far a "quantum collapse" extends; the Copenhagen "theory" (it does
not even deserve the phrase) is fitted to the facts post-facto using
this informal parameter. We eliminate this ill-specified adjunct of the
"quantum collapse", delete the strange interloper that is so utterly
incompatible with the quiet elegance of unitary evolution, just subtract
"collapse" entirely from the theory, and lo, we arrive at exactly the
same experimental predictions - except that predictions are delivered in
advance, rather than fitted post-facto. Everett tells us exactly how to
calculate when decoherence occurs and how much decoherence it is, all
under exactly the same quantum laws that are already necessarily
postulated to explain "uncollapsed" behaviors.

As a slight side effect we find that "worlds" (in a quantum
configuration space filled with swirling clouds of probability amplitude
in close mutual causal connection) "fork" (a cloud of amplitude develops
into separate clouds, groups of points in configuration space
interacting with each other but not with nearby clouds of amplitude), a
phenomenon interpreted by embedded observers as the other clouds
"vanishing". But it would be exceedingly strange to take an elegant
theory which describes exactly how the clouds diverge, and adjoin a
weird and grossly unnecessary postulate which says that as soon as two
clouds fall out of causal contact (which, according to Everett, is not a
discontinuous process, but a smooth one), all but one of the diverging
clouds suddenly vanishes from quantum configuration space (when? why?)

I emphasize that many-worlds is simply the straightforward extrapolation
of quantum theory exactly as it stands, with the unnecessary "collapse
postulate" eliminated. Quantum theory already yields decoherence. And
decoherence is sufficient to explain - nay, predict quantitatively in
advance - everything observed. We do not need to see it post facto and
call it a "collapse", afterward saying that it was caused by an
"observation", and lift our hands and shrug over why the observation
collapsed only so much and no more. Under Everett, all matter in the
universe is governed by exactly the same laws. There is no
distinguished event of "observation".

Now that I understand many-worlds I cannot imagine a quantum theory that
works any other way. It is like understanding natural selection and
then trying to imagine exactly the same biology except that it works by
"elan vital". Elan vital was an early misinterpretation of biology,
grossly ad-hoc and post-facto. The same may be said of Copenhagen and
quantum mechanics. When they set forth the Schrodinger equation they
had *already* explained, formally, with a theory capable of making
advance predictions, all that they had observed, without any need of a
collapse postulate; yet no one realized that the Schrodinger equation
sufficed by itself, until Everett wrote his beautiful paper years later.
  So they adjoined a collapse postulate, awkward and ill-specified and
informal and out of joint with the rest of physics. As if angel's wings
had been adjoined to Newton's equations to fulfill the task of pushing
planets about in the sky, because no one had thought to apply Newton's
equations to planets and see that the task of explaining was already
done - until a few decades later; and then people said, "Oh, but it is
already explained, it is done by angel's wings. And since the angel's
wings already explain the motions of the planets - we just look and
whatever we see, we say it is the angel's wings - your theory can never
be proven."

As a slight side effect of Everett's simpler quantum mechanics, obtained
*purely* by eliminating one awkward dangling postulate from a theory
already complete without it, we find predicted the high-level phenomenon
previously interpreted as "collapse" caused by "observation", and now
revealed as diverging clouds of amplitude - that is, forking worlds.
But for one who has already come to terms with the spatial infinity of
the universe, this should be no additional burden.

I have not used the term "MWI". Many-worlds is not an "interpretation".
  Many-minds, the deranged mad cousin of Everett, is an "interpretation"
and one which makes no sense. Copenhagen is an "interpretation".
Many-worlds is a unified theory that applies to quantum fields, period;
making no mention of observers, minds, or anything else. MW is not an
"interpretation". It is a formal model, unlike its competitors.

> Pardon my incredulity, but I find your statement offensive; and doubly
> so due to your having presented zero justification for your strange
> slander.

These are the possibilities:

1) Harvey has not seen the elegance of the math, and having not seen
the elegance of the math, is extremely disturbed by the possibility of
himself forking a million times per second.

2) Harvey has enough knowledge that he *should* have seen the math, but
is extremely disturbed by the prospect of forking a million times per
second, and so he searches for an excuse.

3) Harvey has already come to terms with the spatial infinity of the
universe implied by contemporary astrophysics, and so many-worlds means
nothing to him emotionally one way or the other; but Harvey has not seen
the elegance of the math, has encountered the wacky philosophical
deranged brother of Everett known as "many-minds", or heard some other
extremely poor justification of many-worlds.

4) Harvey has not come to terms with spatial infinity, so MW would be a
new emotional shock to him, and also he has not heard the good physics
reasons for MW. This would explain his reaction.

> Call me crazy for suggesting this, but how 'bout we avoid dismissing a
> posit of physics found plausible by a number of actual physicists

63% according to that legendary informal poll. Certainly a very large
number of prominent physicists. That is mere argument from authority,
of course. But I see no reason to suppose that these prominent
physicists are messianic transhumanists, when so great a bounty of
mathematical elegance lies at hand, to explain their choice of explanation.

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