[SEQ RERUN] Spooky Action at a Distance

MinibearRex

Today's post, Spooky Action at a Distance: The No-Communication Theorem was originally published on 05 May 2008. A summary (taken from the LW wiki):

As Einstein argued long ago, the quantum physics of his era - that is, the single-global-world interpretation of quantum physics, in which experiments have single unique random results - violates Special Relativity; it imposes a preferred space of simultaneity and requires a mysterious influence to be transmitted faster than light; which mysterious influence can never be used to transmit any useful information. Getting rid of the single global world dispels this mystery and puts everything back to normal again.

Discuss the post here (rather than in the comments to the original post).

This post is part of the Rerunning the Sequences series, where we'll be going through Eliezer Yudkowsky's old posts in order so that people who are interested can (re-)read and discuss them. The previous post was Bell's Theorem: No EPR "Reality", and you can use the sequence_reruns tag or rss feed to follow the rest of the series.

Sequence reruns are a community-driven effort. You can participate by re-reading the sequence post, discussing it here, posting the next day's sequence reruns post, or summarizing forthcoming articles on the wiki. Go here for more details, or to have meta discussions about the Rerunning the Sequences series.

Today's post, Spooky Action at a Distance: The No-Communication Theorem was originally published on 05 May 2008. A summary (taken from the LW wiki):

As Einstein argued long ago, the quantum physics of his era - that is, the single-global-world interpretation of quantum physics, in which experiments have single unique random results - violates Special Relativity; it imposes a preferred space of simultaneity and requires a mysterious influence to be transmitted faster than light; which mysterious influence can never be used to transmit any useful information. Getting rid of the single global world dispels this mystery and puts everything back to normal again.

I agree that the problem of extending MWI (and for that matter, any interpretation of QM) to quantum field theory is a very difficult one. There is good reason to think that one of the central tenets of MWI -- wavefunction realism -- will not survive the transition. I said in a response to Villam's question that the fundamental ontology of the MWI is a universal wavefunction on configuration space. This is the view promoted by Eliezer in his QM sequence. It's an elegant view, but unfortunately its appeal falls apart when you start looking at QFT.

Part of the problem is that in QFT there is no precise configuration space. Particle number isn't conserved in the theory, and particles (being non-fundamental) do not have precisely defined masses, charges and positions. It is very different from the simple case where we can construct a space consisting of the exact configuations of a fixed number of particles.

Also, unlike in non-relativistic QM, operators in QFT are associated with particular regions of space-time. For instance, there are separate field operators associated with every space-time point. Physical space-time is much more entangled with the fundamentals of the theory than it is in non-relativistic QM.

So I think the QM sequence should be accompanied by a huge caveat. The form of MWI advocated there is (I think) the best interpretation available for non-relativistic QM. However, many of the basic lessons of the sequence no longer apply when we are dealing with QFT. And the true physical theory is likely to be a lot closer to QFT than non-relativistic QM. I still think our best bet is to build a broadly MWI-like non-collapse interpretation for QFT, but I suspect it will look quite different from the MWI we all know and love.

Is there any papers that asses this problem ? I can't say I've heard any proponents of MWI acknowledge problems with relativity?

4Viliam_Bur14y

Thanks for explanation. So I guess the question is still open (of course, the word "open" refers to our maps, not to the territory). If I understand it correctly: * relativity assumes that the universe is local in space * quantum physics assumes that the universe is local in configuration space and the problem, as I see it, is we don't even have a nice definition of "configuration space" that wouldn't violate the assumption of space locality. If I understand it correctly, some people are trying to fix this by replacing configuration spaces by histories of the universe, but... imagining a history of the whole universe up to the specific point of space-time as a fundamental particle of physics, that feels wrong. Well, maybe it is right -- we should not rely on our intuition derived from macroscopic events -- but maybe we just didn't find a better solution yet.

2Shmi14y

That's a matter of taste, since there is no way to resolve this except on aesthetic grounds. [...] Indeed. Including the quote in the OP, which makes no sense as stated. [...] Or else, dispense with interpretations and do physics instead.

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