Particles break light-speed limit?

Does it even make sense to say "won't", or for that matter bring up anthropic considerations, in reference to causality violation?

I'm not sure. If a universe allows sufficient causality violation then it may be that it will be too unstable for observers to arise in that universe. But I'm not sure about that. This may be causality chauvinism.

Does it even make sense to say "won't" [...] in reference to causality violation?

Yes. (Leave out the anthropics, when that makes sense to bring up is complicated.)

Most of the reason for saying:

If there are ways to violate causality they are likely restrictive enough that we can't use them to violate causality prior to when we knew about the methods (roughly).

... are somewhat related to "causality doesn't appear to be violated". If (counterfactually) causality can be violated then it seems like it probably hasn't happened yet. This makes it a lot more likely that causality violations (like wormholes and magic) that are discovered in the future will not affect things before their discovery. This includes the set of (im)possible worlds in which prior-to-the-magic times cannot be interfered with and also some other (im)possible worlds in which it is possible but doesn't happen because it is hard.

An example would be faster-than-light neutrinos. It would be really damn hard to influence the past significantly with such neutrinos with nothing set up to catch them. It would be much easier to set up a machine to receive messages from the future.

It may be worth noting that "causality violation" does not imply "complete causality meltdown". The latter would definitely make "won't" rather useless.

In the context of almost every proposed causality violation mechanism I've seen seriously discussed, it really is can't, not won't.

There are plenty of mechanisms in which can't applies. There are others which don't have that limitation. I don't even want to touch what qualifies as 'seriously discussed'. I'm really not up to date with which kinds of time travel are high status.

And Einstein was better at the same sort of philosophy and used it to predict new physical laws that he thought should have the right sort of style (though I'm not trying to do that, just read off the style of the existing model). But anyway, I'd pay $20,000 to find out I'm that wrong - what I want to eliminate is the possibility of paying $20,000 to find out I'm right.

Username, you're having a small conversion experience here, going from "causality is local" to "wavefunction collapse is preposterous" to "I understand quantum suicide" to "I'd better sign up for cryonics once I graduate" in rapid succession. It's a shame we can't freeze you right now, and then do a trace-and-debug of your recent thoughts, as a case study.

This was a somewhat muddled comment from Eliezer. Local causality does not imply an upper speed limit on how fast causal influences can propagate. Then he equivocates between locality within a configuration and locality within configuration space. Then he says that if only everyone in physics thought like this, they wouldn't have wrong opinions about how QM works. I can only guess how you personally relate all that to decoherence. And from there, you get to increased confidence in cryonics. It could only happen on Less Wrong. :-)

ETA: Some more remarks:

Locality does not imply a maximum speed. Locality just means that causes don't jump across space to their effects, they have to cross it point by point. But that says nothing about how fast they cross it. You could have a nonrelativistic local quantum mechanics with no upper speed limit. Eliezer is conflating locality with relativistic locality, which is what he is trying to derive from the assumption of locality. (I concede that no speed limit implies a de-facto or practical nonlocality, in that the whole universe would then be potentially relevant for what happens here in the "next moment"; some influence moving at a googol light-years per second might come crashing in upon us.)

Equivocating between locality in a configuration and locality in a configuration space: A configuration is, let's say, an arrangement of particles in space. Locality in that context is defined by distance in space. But configuration space is a space in which the "points" themselves are whole configurations. "Locality" here refers to similarity between whole configurations. It means that the amplitude for a whole configuration is only immediately influenced by the amplitudes for infinitesimally different whole configurations.

Suppose we're talking about a configuration in which there are two atoms, A and B, separated by a light-year. The amplitude for that configuration (in an evolving wavefunction) will be affected by the amplitude for a configuration which differs slightly at atom A, and also by the amplitude for a configuration which differs slightly at atom B, a light-year away from A. This is where the indirect nonlocality of QM comes from - if you think of QM in terms of amplitude flows in configuration space: you are attaching single amplitudes to extended objects - arbitrarily large configurations - and amplitude changes can come from very different "directions" in configuration space.

Eliezer also talks about amplitudes for subconfigurations. He wants to be able to say that what happens at a point only depends on its immediate environment. But if you want to talk like this, you have to retreat from talking about specific configurations, and instead talk about regions of space, and the quantum state of a "region of space", which will associate an amplitude with every possible subconfiguration confined to that region.

This is an important consideration for MWI, evaluated from a relativistic perspective, because relativity implies that a "configuration" is not a fundamental element of reality. A configuration is based on a particular slicing of space-time into equal-time hypersurfaces, and in relativity, no such slicing is to be preferred as ontologically superior to all others. Ultimately that means that only space-time points, and the relations between them (spacelike, lightlike, timelike) are absolute; assembling sets of points into spacelike hypersurfaces is picking a particular reference frame.

This causes considerable problems if you want to reify quantum wavefunctions - treat them as reality, rather than as constructs akin to probability distributions - because (for any region of space bigger than a point) they are always based on a particular hypersurface, and therefore a particular notion of simultaneity; so to reify the wavefunction is to say that the reference frame in which it is defined is ontologically preferred. So then you could say, all right, we'll just talk about wavefunctions based at a point. But building up an extended wavefunction from just local information is not a simple matter. The extended wavefunction will contain entanglement but the local information says nothing about entanglement. So the entanglement has to come from how you "combine" the wavefunctions based at points. Potentially, for any n points that are spacelike with respect to each other, there will need to be "entanglement information" on how to assemble them as part of a wavefunction for configurations.

I don't know where that line of thought takes you. But in ordinary Copenhagen QM, applied to QFT, this just doesn't even come up, because you treat space-time, and particular events in space-time, as the reality, and wavefunctions, superpositions, sums over histories, etc, as just a method of obtaining probabilities about reality. Copenhagen is unsatisfactory as an ontological picture because it glosses over the question of why QM works and of what happens in between one "definite event" and the next. But the attempt to go to the opposite interpretive pole, and say "OK, the wavefunction IS reality" is not a simple answer to your philosophical problems either; instead, it's the beginning of a whole new set of problems, including, how do you reify wavefunctions without running foul of relativity?

Returning to Eliezer's argument, which purports to derive the existence of a causal speed-limit from a postulate of "locality": my critique is as informal and inexact as his argument, but perhaps I've at least shown that this is not as simple a matter as it may appear to the uninformed reader. There are formidable conceptual problems involved just in getting started with such an argument. Eliezer has the essentials needed to think about these topics rigorously, but he's passing over crucial details, and he may thereby be overlooking a hole in his intuitions. In mathematics, you may start out with a reasonable belief that certain objects always behave in a certain way, but then when you examine specifics, you discover a class of cases which work in a way you didn't anticipate.

What if you have a field theory with no speed limit, but in which significant and ultra-fast-moving influences are very rare; so that you have an effective "locality" (in Eliezer's sense), with a long tail of very rare disruptions? Would Eliezer consider that a disproof of his intuitive idea, or an exception which didn't sully the correctness of the individual insight? I have no idea. But I can say that the literature of physics is full of bogus derivations of special relativity, the Born rule, the three-dimensionality of space, etc. This derivation of "c" from Pearlian causal locality certainly has the ingredients necessary for such a bogus derivation. The way to make it non-bogus is to make it deductively valid, rather than just intuitive. This means that you have to identify and spell out all the assumptions required for the deduction.

Ok, I sit corrected. This is what happens when an experimentalist tries to remember his theory courses. :)

You need to provide links because I read a fair bit on the subject and don't recall this.

That's a fair request. I don't really have the time to go digging for those details, though. If you feel so inspired, again I'd point to the work done at the Stanford Research Institute (or at least I think it was that) where they did a ridiculous number of trials of all kinds and did get several standard deviations away from the expected mean predicted based on the null hypothesis. I honestly don't remember the numbers at all, so you could be right that there has never been anything like a six-s.d. deviation in parapsychological experiments. I seem to recall that they got somewhere around ten - but it has been something like six years since I read anything on this topic.

That said, I get the feeling there's a bit of goalpost-moving going on in this discussion. In Eliezer's original reference to parapsychology as the control group for science, his point was that there are some amazingly subjective effects that come into play with frequentist statistics that could account for even the good (by frequentist standards) positive-result studies from parapsychology. I agree, there's a lot of problem with things like publication bias and the like, and that does offer an explanation for a decent chunk of parapsychology's material. But to quote Eliezer:

Parapsychology, the control group for science, would seem to be a thriving field with "statistically significant" results aplenty. Oh, sure, the effect sizes are minor. Sure, the effect sizes get even smaller (though still "statistically significant") as they collect more data. Sure, if you find that people can telekinetically influence the future, a similar experimental protocol is likely to produce equally good results for telekinetically influencing the past. Of which I am less tempted to say, "How amazing! The power of the mind is not bound by time or causality!" and more inclined to say, "Bad statistics are time-symmetrical." But here's the thing: Parapsychologists are constantly protesting that they are playing by all the standard scientific rules, and yet their results are being ignored - that they are unfairly being held to higher standards than everyone else. I'm willing to believe that. It just means that the standard statistical methods of science are so weak and flawed as to permit a field of study to sustain itself in the complete absence of any subject matter.

I haven't looked at the CERN group's methods in enough detail to know if they're making the same kind of error. I'm just trying to point out that we can't assign an abysmally low probability to their making a common kind of statistical error that finds a small-but-low-p-value effect without simultaneously assigning a lower probability to parapsychologists making this same mistake than Eliezer seems to.

And to be clear, I am not saying "Either the CERN group made statistical errors or telepathy exists." Nor am I trying to defend parapsychology. I'm simply pointing out that we have to be even-handed in our dismissal of low-p-value thinking.

Ok. In that case this hypothesis seriously fails.

Oh, sorry, I was confused and thought you were offering the bet the other way around.

In order for this to be from an error in measurement you need to be a few meters off (18 meters if that's the only problem). There are standard GPS techniques and surveying techniques which can be used to get very precise values. They state in the paper and elsewhere that they are confident to around 30 cm. Differential GPS can have accuracy down to about 10-15 cm, and careful averaging of standard GPS can get you in the range of 20 cm, so this isn't at all implausible but it is still a definite potential source of error.

A more plausible issue is that since parts of the detectors are underground they didn't actively use GPS for those parts. But even then, a multiple meter error seems unlikely, and 18 meters is a lot. It is possible that there's a combination of errors all going in the same direction, say a meter error in the distance, a small error in the clock calibration, etc. And all of that add up even as each error remains small enough that it is difficult to detect. But they've been looking at things really closely so one would then think that at least one of the errors would turn up.

Yup.