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EHeller comments on Welcome to Less Wrong! (5th thread, March 2013) - Less Wrong
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I have a phd in physics (so I have at least some technical skill in this area) and find the QM sequence's argument for many worlds unconvincing. You lead the reader toward a false dichotomy (Copenhagen or many worlds) in order to suggest that the low probability of copenhagen implies many worlds. This ignores a vast array of other interpretations.
Its also the sort of argument that seems very likely to sway someone with an intro class in college (one or two semesters of a Copenhagen based shut-up-and-calculate approach), precisely because having seen Copenhagen and nothing else they 'know just enough to be dangerous', as it were.
For me personally, the quantum sequence threw me into some doubt about the previous sequences I had read. If I have issues with the area I know the most about, how much should I trust the rest? Other's mileage may vary.
Actually, attempting to steelman the QM Sequence made me realize that the objective collapse models are almost certainly wrong, due to the way they deal with the EPR correlations. So the sequence has been quite useful to me.
On the other hand, it also made me realize that the naive MWI is also almost certainly wrong, as it requires uncountable worlds created in any finite instance of time (unless I totally misunderstand the MWI version of radioactive decay, or any emission process for that matter). It has other issues, as well. Hence my current leanings toward some version of RQM, which EY seems to dislike almost as much as his straw Copenhagen, though for different reasons.
Right, I've had a similar experience, and I heard it voiced by others.
As a result of re-examining EY's take on epistemology of truth, I ended up drifting from the realist position (map vs territory) to an instrumentalist position (models vs inputs&outputs), but this is a topic for another thread. I am quite happy with the sequences related to cognitive science, where, admittedly, I have zero formal expertise. But they seem to match what the actual experts in the field say.
I am on the fence with the free-will "dissolution", precisely because I know that I am not qualified to spot an error and there is little else out there in terms of confirming evidence or testable predictions.
I am quite skeptical about the dangers of AGI x-risk, mainly because it seems to extrapolate too far beyond what is known into the fog of the unknown future, though do I appreciate quite a few points made in the relevant sequences. Again, I am not qualified to judge their validity.
How is that any more problematic than doing physics with real or complex numbers in the first place?
It means that EY's musings about the Eborians splitting into the world's of various thicknesses according to Born probabilities no longer make any sense. There is a continuum of worlds, all equally and infinitesimally thin, created every picosecond.
The way I understand it, it's not that “new” worlds are created that didn't previously exist (the total “thickness” (measure) stays constant). It's that two worlds that looked the same ten seconds ago look different now.
That's a common misconception. In the simplest case of the Schrodinger' cat, there are not just two worlds with cat is dead or cat is alive. When you open the box, you could find the cat in various stages of decomposition, which gives you uncountably many worlds right there. In a slightly more complicated version, where energy and the direction of the decay products are also measurable (and hence each possible value is measured in at least one world), your infinities keep piling up every which way, all equally probable or nearly so.
(By “two” I didn't mean to imply ‘the only two’.)
Which two out of the continuum of world then did you imply, and how did you select them? I don't see any way to select two specific worlds for which "relative thickness" would make sense. You can classify the worlds into "dead/not dead at a certain instance of time" groups whose measures you can then compare, of course. But how would you justify this aggregation with the statement that the worlds, once split, no longer interact? What mysterious process makes this aggregation meaningful? Even if you flinch away from this question, how do you select the time of the measurement? This time is slightly different in different worlds, even if it is predetermined "classically", so there is no clear "splitting begins now" moment.
It gets progressively worse and more hopeless as you dig deeper. How does this splitting propagate in spacetime? How do two spacelike-separated splits merge in just the right way to preserve only the spin-conserving worlds of the EPR experiment and not all possibilities? How do you account for the difference in the proper time between different worlds? Do different worlds share the same spacetime and for how long? Does it mean that they still interact gravitationally (spacetime curvature = gravity). What happens if the spacetime topology of some of the worlds changes, for example by collapsing a neutron star into a black hole? I can imagine that these questions can potentially be answered, but the naive MWI advocated by Eliezer does not deal with any of this.
That fails to answer the question- the Schroedinger equation isn't lorentz invariant (its not even fully Galilean invariant), so it can't tell you much about spacetime.
You can't just replace Schroedinger with Dirac or Klein-Gordon without leading inevitably to a field theory, which opens up new cans of worms.
A mental picture of thermodynamic irreversibility as a directed tree is indeed an appealing one. It becomes less appealing once your tree does not have any well-defined vertices or edges due to the issues I have outlined.
The SE is non-relativistic, so it has absolutely nothing to say about propagation in spacetime. It does not even describe emission or absorption, an essential part of decoherence. You have to go fully monty QFT to talk about signal propagation, but no one talks about MWI in the context of QFT, as far as I know.
In MWI [eigen]states correspond to worlds, so I don't know what it means. I also don't know what you mean by mergeable states.
This implies gravitational interaction between non-interacting worlds, so do they interact or don't they?
Feel free to quote... Just not his quantum consciousness speculations.
coughmeasurecough
Is there actually any physicists that find QM sequence to be making such a strongly compelling case for MWI as EY says it does?
I know Mitchell Porter is likewise a physicist and he's not convinced at all either.
Mitchell Porter also advocates Quantum Monadology and various things about fundamental qualia. The difference in assumptions about how physics (and rational thought) works between Eliezer (and most of Eliezer's target audience) and Mitchell Porter is probably insurmountable.
Yeah, and EY [any of the unmentionable things].
For other point, scott aaronson doesn't seem convinced either. Robin Hanson, while himself (it seems) a MWI believer but doesn't appear to think that its so conclusively settled.
The relevance of Porter's physics beliefs is that any reader who disagrees with Porter's premises but agrees with the premises used in an article can gain little additional information about the quality of the article by learning that Porter is not convinced by it. ie. Whatever degree of authority Mitchell Porter's status grants goes (approximately) in the direction of persuading the reader to adopt those different premises.
In this way mentioning Porter's beliefs is distinctly different from mentioning the people that you now bring up:
What one can learn is that the allegedly 'settled' and 'solved' is far from settled and solved and is a matter of opinion as of now. This also goes for qualia and the like; we haven't reduced them to anything, merely asserted.
It extends all the way up, competence wise - see Roger Penrose.
It's fine to believe in MWI if that's where your philosophy falls, its another thing entirely to argue that belief in MWI is independent of priors and a philosophical stance, and yet another to argue that people fail to be swayed by a very biased presentation of the issue which omits every single point that goes in favour of e.g. non-realism, because they are too irrational or too stupid.
No, that set of posts goes on at some length about how MWI has not yet provided a good derivation of the Born probabilities.
But I think it does not do justice to what a huge deal the Born probabilities are. The Born probabilities are the way we use quantum mechanics to make predictions, so saying "MWI has not yet provided a good derivation of the Born probabilities" is equivalent to "MWI does not yet make accurate predictions," I'm not sure thats clear to people who read the sequences but don't use quantum mechanics regularly.
Also, by omitting the wide variety of non-Copenhagen interpretations (consistent histories, transactional, Bohm, stochastic-modifications to Schroedinger,etc) the reader is lead to believe that the alternative to Copenhagen-collapse is many worlds, so they won't use the absence of Born probabilities in many worlds to update towards one of the many non-Copenhagen alternatives.
Note that the Born probabilities really obviously have something to do with the unitarity of QM, while no single-world interpretation is going to have this be anything but a random contingent fact. The unitarity of QM means that integral-squared-modulus quantifies the "amount of causal potency" or "amount of causal fluid" or "amount of conserved real stuff" in a blob of the wavefunction. It would be like discovering that your probability of ending up in a computer corresponded to how large the computer was. You could imagine that God arbitrarily looked over the universe and destroyed all but one computer with probability proportional to its size, but this would be unlikely. It would be much more likely (under circumstances analogous to ours) to guess that the size of the computer had something to do with the amount of person in it.
The problems with Copenhagen are fundamentally one-world problems and they go along with any one-world theory. If I honestly believed that the only reason the QM sequence wasn't convincing was that I didn't go through every single one-world theory to refute them separately, I could try to write separate posts for RQM, Bohm, and so on, but I'm not convinced that this is the case. Any single-world theory needs either spooky action at a distance, or really awful amateur epistemology plus spooky action at a distance, and there's just no reason to even hypothesize single-world theories in the first place.
(I'm not sure I have time to write the post about Relational Special Relativity in which length and time just aren't the same for all observers and so we don't have to suppose that Minkowskian spacetime is objectively real, and anyway the purpose of a theory is to tell us how long things are so there's no point in a theory which doesn't say that, and those silly Minkowskians can't explain how much subjective time things seem to take except by waving their hands about how the brain contains some sort of hypothetical computer in which computing elements complete cycles in Minkowskian intervals, in contrast to the proper ether theory in which the amount of conscious time that passes clearly corresponds to the Lorentzian rule for how much time is real relative to a given vantage point...)
And yet it proclaims the issue settled in favour of MWI and argues of how wrong science is for not settling on MWI and so on. The connection - that this deficiency is why MWI can't be settled on, sure does not come up here. Speaking of which, under any formal metric that he loves to allude to (e.g. Kolmogorov complexity), MWI as it is, is not even a valid code for among other things this reason.
It doesn't matter how much simpler MWI is if we don't even know that it isn't too simple, merely guess that it might not be too simple.
edit: ohh, and lack of derivation of Born's rules is not the kind of thing I meant by argument in favour of non-realism. You can be non-realist with or without having derived Born's rules. How QFT deals with relativistic issues, as outlined by e.g. Mitchell Porter , is a quite good reason to doubt reality of what goes on mathematically in-between input and output. There's a view that (current QM) internals are an artefact of the set of mathematical tricks which we like / can use effectively. The view that internal mathematics is to the world as rods and cogs and gears inside a WW2 aiming computer are to a projectile flying through the air.
Are they, though? Irrational or stupid?
I defected from physics during my Master's, but this is basically the impression I had of the QM sequence as well.