[SEQ RERUN] Collapse Postulates
post by MinibearRex · 2012-04-30T06:49:51.041Z · LW · GW · Legacy · 8 commentsToday's post, Collapse Postulates was originally published on 09 May 2008. A summary (taken from the LW wiki):
Early physicists simply didn't think of the possibility of more than one world - it just didn't occur to them, even though it's the straightforward result of applying the quantum laws at all levels. So they accidentally invented a completely and strictly unnecessary part of quantum theory to ensure there was only one world - a law of physics that says that parts of the wavefunction mysteriously and spontaneously disappear when decoherence prevents us from seeing them any more. If such a law really existed, it would be the only non-linear, non-unitary, non-differentiable, non-local, non-CPT-symmetric, acausal, faster-than-light phenomenon in all of physics.
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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 Quantum Non-Realism, and you can use the sequence_reruns tag or rss feed to follow the rest of the series.
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8 comments
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comment by Random832 · 2012-04-30T12:31:54.639Z · LW(p) · GW(p)
The only phenomenon in all of physics that violates Liouville's Theorem (has a many-to-one mapping from initial conditions to outcomes).
I don't know what Liouville's Theorem is, but this sounds like an objection to not being able to run time backwards.
Replies from: Oscar_Cunningham↑ comment by Oscar_Cunningham · 2012-04-30T13:05:00.900Z · LW(p) · GW(p)
Liouville's Theorem says that if you know that the state of the universe has to be one of the states in a set A, and then as time passes you run each universe in that set forwards, so that now you know that the universe is in set A', then the "volume" of sets A and A' has to be the same.
comment by RobertLumley · 2012-04-30T14:15:23.047Z · LW(p) · GW(p)
At first scan, I read this post as "[SEQ RERUN] Collapse Prostitutes". I was very confused.
comment by shminux · 2012-04-30T06:56:34.453Z · LW(p) · GW(p)
WHAT DOES THE GOD-DAMNED COLLAPSE POSTULATE HAVE TO DO FOR PHYSICISTS TO REJECT IT? KILL A GOD-DAMNED PUPPY?
Be experimentally proven inferior to some other model. Hasn't happened yet.
Replies from: Swimmy↑ comment by Swimmy · 2012-04-30T17:24:19.234Z · LW(p) · GW(p)
I propose a theory: It isn't the "strong nuclear interaction" that binds protons and neutrons together, it's actually very tiny little angels that live in between the particles and hold them together. They are also responsible for binding quarks together.
What's that you say? "Invisible fairies" is a complicated hypothesis that needs extra evidence to contend with strong nuclear interaction theory? Well, they are experimentally no different, so you need to directly falsify my angel theory.
What's that you say? The existence of indetectable invisible magical sapient beings that are too small to contain any known possible mind configurations violates some known laws of physics, so our Bayesian prior should be highly weighed against them? Who cares? I'm going to believe in them until you prove that they are experimentally inferior to strong nuclear interaction theory.
(By the way, "Jesus holds atoms together" is genuinely proposed by some.)
Replies from: shminux↑ comment by shminux · 2012-04-30T17:53:51.459Z · LW(p) · GW(p)
By all means, show that your TiLiABiNT theory (tiny little angels binding nucleons together) explains all of the observed nuclear phenomena and predicts as much as the currently popular TiLiRuBaBiNT (tiny little rubber bands binding nucleons together) theory.
What's that you say? The existence of indetectable invisible magical sapient beings that are too small to contain any known possible mind configurations violates some known laws of physics, so our Bayesian prior should be highly weighed against them?
No, the onus is on you to show that TiLiABiNT is better than TiLiRuBaBiNT, if you want me to adopt any specific interpretation. Until then, I will happily use the relevant math without worrying whether the rubber bands are magical or sapient.
Oh, and by the way, that straw-evolutionist cartoon is great. Someone really skilled at Dark Arts did an excellent job. Took me quite some time to figure out what is going on, back when I came across it for the first time years ago, before knowing anything about rationality.
Replies from: Maelin↑ comment by Maelin · 2012-05-09T07:11:20.677Z · LW(p) · GW(p)
No, the onus is on you to show that TiLiABiNT is better than TiLiRuBaBiNT, if you want me to adopt any specific interpretation. Until then, I will happily use the relevant math without worrying whether the rubber bands are magical or sapient.
Right, but now let's imagine a world in which you heard TiLiABiNT (henceforth: angel theory) before you heard TiLiRuBaBiNT (henceforth: rubber theory)..Might you not equally be arguing "No, the onus is on you to show that rubber theory is better than angel theory"?
If your decision process when faced with competing, equally supported theories is simply to stick with whichever one you happened to hear first, if you deny that (quantified) application of Occam's Razor is a worthwhile tool to apply to competing theories that explain observations equally well, then you open yourself to holding beliefs with many useless, nonfunctional extra attachments stuck on. You could just as easily have heard angel theory before rubber theory. You want a mind that would settle on the less ridiculous of the two regardless of what order it heard them in.
Replies from: asr↑ comment by asr · 2012-05-09T08:13:49.983Z · LW(p) · GW(p)
The costs to switch beliefs are sometimes high. In particular, changing scientific theories is very costly in terms of retraining, revising textbooks and curricula, trying to figure out which past results are still meaningful and which are now incoherent, etc. I am prepared to tolerate a certain amount of theoretical cruft for the sake of having old research papers remain readily readable.
MWI vs collapse theories is an interesting case in point. There doesn't seem to be a simple and clean way to derive the Born Rule in MWI. From a practical point of view, it's much better to just stipulate the Born rule -- to say that we can ignore any part of the wave function that didn't match with our measurement -- than it is to assume this exponentially* growing entangled state that we will never perceive. It might be that MWI is simpler in some sense, but talking about "collapse" is a much clearer way to explain what we are really doing mathematically.
*I am using the word in its precise sense.