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shminux comments on If Many-Worlds Had Come First - Less Wrong
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rQM subtracts objective state and therefore does not have MWI's basis problem.
I tend to agree with you. As I said before, to me RQM to MWI is what "shut up and calculate" is to Copenhagen. Unfortunately, I have a feeling that I am missing some important point Eliezer is making (he tends to make important points, in my experience). For example, in the statement
I do not understand where, in his opinion, RQM adds a complication to (what?) epistemology.
Instead of having causal processes which are real, we now need causal processes which are 'real relative to' other causal processes. To prevent the other worlds from being real enough to have people inside them, we need to insist very loudly that this whole diagram of what is 'real relative to' other things, is not itself real. I am not clear on how this loud insistence can be accomplished. Also, since only individual points in configuration space allow one particle to say that another particle is in an exact position and have this be 'real', if you take a blob of amplitude large enough to contain a person's causal process, you will find that elements of a person disagree about what is real relative to them...
...and all these complications are just pointless, there's no need for our ontology to have a notion like 'real relative to' instead of just talking about causes and effects. RQM doesn't even get any closer to explaining the Born probabilities, so why bother? It's exactly like a version of Special Relativity that insists on talking about 'real lengths relative to' instead of observer-invariant Minkowskian spacetime.
In RQM, there are no other worlds in the MWI sense. MWI allows observers to make contradictory measurements, such as |up> and |down> and then tries to remove the contradiction by indexing each measurement to its own world. rQM does not allow observers to make contradictory measurements, so there is no need to wish away worlds, because there was never a need to introduce them.
"However, the comparison does not lead to contradiction because the comparison is itself a physical process that must be understood in the context of quantum mechanics. Indeed, O′ can physically interact with the electron and then with the l.e.d. (or, equivalently, the other way around). If, for instance, he finds the spin of the electron up, quantum mechanics predicts that he will then consistently find the l.e.d. on (because in the first measurement the state of the composite system collapses on its [spin up/l.e.d. on] component). That is, the multiplicity of accounts leads to no contradiction precisely because the comparison between different accounts can only be a physical quantum interaction. This internal self-consistency of the quantum formalism is general, and it is perhaps its most remarkable aspect. This self consistency is taken in relational quantum mechanics as a strong indication of the relational nature of the world." --SEP
rQM has an ontology. It's an ontology of relations. rQM denies state -- non-relational infmoration. rQM does not need to say anything is real relativee to anything else -- only that some information is not available to some systems.
I have no idea what that means.
My best guess at the lack of agreement here is the difference in yours and mine ontology at a rather basic level. Specifically, your ontology seems to be
whereas mine does not have "the thingy that determines my experimental results" and treats these results as primitive instead. As a consequence, everything is a model ("belief"), and good models predict experimental results better. So there is no need to use the term "real" except maybe as a shorthand for the territory in the map-territory model (which is an oft useful model, but only a model).
You can probably appreciate that this ontological difference makes statements like
where the term "real" is repeated multiple times, lose meaning if one only cares about making accurate models.
Now, I cannot rule out that your ontology is better than my ontology in some sense of the term "better" acceptable to me, but that would be a discussion to be had first, before going into the interpretational problems of Quantum Mechanics. I can certainly see how adopting your ontology of objective reality may lead one to dislike RQM, which evades pinning down what reality is in the RQM view. On the other hand, you can probably agree that removing objective reality from one's ontology would make MWI an unnecessary addition to a perfectly good model called relational quantum mechanics.
This sounds like 'shut up and calculate' to me. After applying "shut up and calculate" to RQM the results are identical to the results of applying "shut up and calculate" to MWI, so there's no reason to claim that you're shutting up about RQM instead of shutting up about MWI or rather just shutting up about quantum mechanics in general, unless you're not really shutting up. To put it another way, there is no such thing as shutting up about RQM or MWI, only shutting up about QM without any attempt to say what underlying state of affairs you are shutting up about.
If that's not what you mean by denying that you intend to talk about a thingy that generates your experimental results and treating the results as primitive, please explain what that was supposed to say.
First, I think that we agree that 'shut up and calculate' reflects the current unfortunate state of affairs, where no other approach is more accurate despite nearly a century of trying. It postulates the Born rule (measurement results in projection onto an eigenstate), something each interpretation also postulates in one form or another, where the term "measurement" is generally understood as an interaction of a simple transparent ( = quantum) system with a complex opaque ( = classical) one. The term decoherence describes how this simple system becomes a part of the complex one it interacts with (and separates from it once the two stop interacting).
Now, I agree that
And indeed I'm not shutting up, because the quantum-classical transition is a mystery to be solved, in a sense that one can hopefully construct a more accurate model (one that predicts new experimental results, not available in "shut up and calculate").
The question is, which are the more promising avenues to build such a model on. RQM suggests a minimal step one has to take, while MWI boldly goes much further, postulating an uncountable (unless limited by the Planck scale) number of invisible new worlds appearing all the time everywhere, without explaining the mysterious splitting process in its own ontology (how does world splitting propagate? how do two spacelike-separated splits interact?).
Now, I am willing to concede that some day some extension of MWI may give a useful new testable prediction and thus will stop being an 'I'. My point is that, unless you postulate reality as ontologically fundamental, MWI is not the smallest increment in modeling the observed phenomenon of the quantum-classical transition.
No mechanism is required, you just get that from the SWE (taken realistically..as it isn't in rQM). Are you a physicist?
This should screen off the title/profession "physicist" entirely, I think. If that's what you meant in the first place, then it wasn't quite clear.
It seems at first like you're asking about academic degrees and titles and tribal levels of authority.
I was surprised at the mistake.
Not sure what SWE stands for.
Schrodinger (Wave) Equation.
Oh. The Schroedinger equation says nothing about the measurement. In all likelihood, a theory of quantum to classical transition would require at least some elements of QFT, as the measurement, as an irreversible process, results in emission of photons, phonons or some other real or quasi-particles. Thus you have to go from the Hilbert space to some sort of Fock space, since the number of particles is not conserved.
No approach is ever more accurate than 'shut up and calculate'. The 'Shut up and calculate' version of Special Relativity, wherein we claim that Minkowski's equations give us classical lengths but refuse to speculate about how this mysterious transition from Minkowski intervals to classical lengths is achieved, is just as accurate as Special Relativity. It's just, well, frankly in denial about how the undermining of your intuition of a classical length is not a good reason to stick your fingers in your ears and go "Nah nah nah I'm not listening" with respect to Minkowski's equations representing physical reality, the way they actually do. You believe this with respect to Special Relativity, and General Relativity, and every other "shut up and calculate" version of every physical theory from chemistry to nuclear engineering - that there's no reason to shut up with respect to these other disciplines. I just believe it with respect to quantum mechanics too.
So do I, and have stated as much. Not sure where the misunderstanding is coming from.
You ought to, however, agree that QM is special: no other physical model has several dozens of interpretations, seriously discussed by physicists and philosophers alike. This is an undisputed experimental fact (about humans, not about QM).
What is so special about QM that inspires interpretations? Many other scientific models are just as counter-intuitive, yet there is little arguing about the underlying meaning of equations in General Relativity (not anymore, anyway) or in any other model. To use your own meta-trick, what is it so special about the Quantum theory (not about the quantum reality, if you believe in such) that inspires people to search for interpretations? Maybe if we answer this reasonably easy cognitive science question first, we can then proceed to productively discuss the merits of various interpretations.
Perhaps you mean the sheer quantity is so great. But there have been, an are, disputes about classical pysyics and relativity. Some of them have been resolved by just beiieving the theory and abandoning contrary intuitions. At one time, atoms were dismissed as a "mere calculational device". Sound familiar?
Sure, every new theory is like that initially. But it only takes a short time for the experts to integrate the new weird ideas, like relative spacetime, or event horizons, or what have you. There is no agreement among the experts about the ontology of QM (beyond the undisputed assertion that head-in-the-sand "shut up and calculate" works just fine), and it's been an unusually long time. Most agree that the wave function is, in some sense, "real", but that's as far as it goes. So the difference is qualitative, not just quantitative. Simply "trusting the SE" gives you nothing useful, as far as the measurement is concerned.
There's certainly one obvious explanation which occurs to me. There being a copy of you in another universe seems more counterintuitive than needing to give up on measuring distances, so it's getting more like the backlash and excuses that natural selection got, or that was wielded to preserve vitalism, as opposed to the case of Special Relativity. Also the simple answer seems to have been very hard to think of due to some wrong turns taken at the beginning, which would require a more complex account of human cognitive difficulty. But either way it doesn't seem at all unnatural compared to backlash against the old Earth, natural selection, or other things that somebody thought was counterintuitive.
You mean that "simple answer" that still can't make predictions?
You need to realize that the "simple answer" isn't so simple- no one has been able to use the axioms for many worlds to make an actual calculation of anything. By kicking away the Born amplitudes, they've kicked away the entire predictive structure of the theory. You are advocating that physicists give up the ability to make predictions!
Its even worse when you go to quantum field theories and try to make many worlds work- the bulk of the amplitude will be centered on "world's" with undefined particle number.
Cat neither dead nor alive until you open the box?
Yeah, that's pretty special, but why?
On a related note, in MWI there is an uncountable number of worlds with the cat is in various stages of decay once the box is open. Is that weird or what.
You have to remember that 'interpretations' of quantum mechanics are actually reformulations of quantum mechanics. Just as classical mechanics can be described by Newton's laws, or one of several action principals (Hamilton/Jacobi,Maupertuis' principle,etc), quantum mechanics has many formulations, each with their own axioms- there is nothing unique about quantum in this sense.
What IS unique about quantum mechanics is that so many interpretations are incomplete. Copenhagen is circular (to make sense of the measurement axiom, you need correspondence principle axiom, but classical needs to be a limit of quantum mechanical.) The measurement problem is a formal problem with the axioms of the theory.
Of course, many worlds is in an even worse position. No one has yet to effectively derive the Born amplitudes which means the interpretation is broken, there is no recipe to extract information about measurements from the theory.
Bohm might be an actual complete interpretation but its nearly impossible to extend the formalism to quantum field theories, Consistent histories is where I put my money- the homogenous history class operator seems potentially like the missing piece.
Hmm, I could never make sense of the formalism of CH (it seems to rely on time-ordering and density matrices, neither of which inspire confidence, given that one expects a relativistically invariant evolution of a pure state), and the popular write-ups sound like advocacy.
This isn't actually correct- there is not a "shut-up-and-calculate" version of many world's- without the born probabilities you can't calculate anything. Maybe someday Deutsch,Wallace or some other enterprising many worlds advocate will show us a way to do calculations without the measurement postulate. That hasn't happened yet, so many worlds does not let us calculate. As far as I know, this inability to calculate is the primary reason physicists reject it.
I'm very curious as to why I'm being downvoted for expressing this sentiment, if any down voter cares to explain, I'd be much obliged.
FYI, "territory" means "territory", not map.
Model of what? If you subtract the ontology from an interpretation, what are you left with knowledge of?
A basis to build a testable model on.
In this and your previous comment, you write as though as though rQM is a different formalism, a different theory, leading to different results. It isn't.
In principle rQM could suggest a different mental picture, and one better capable of inspiring further models that will make successful predictions. (Assuming shminux's bizarre positivist-like approach admits the existence of mental pictures.) The "better capable" part seems unlikely to this layman. Feynman's path integrals have a very MWI-like feel to me, and Feynman himself shared that impression when he wrote the book with Hibbs. But since paths that go back in time seem to pose a problem for Eliezer's causality-based approach, perhaps shminux has some reason for preferring rQM that I don't see. I'm still betting against it.
Feel free to quote the statement that led you to such a strange conclusion.
and
Maybe he's counting the lack of an objective state as additional information?
Basic question I probably should've asked earlier: Does shminux::RQM entail not-MWI?
If the answer is "no" then shminux::RQM is indeed plausibly shutting up, since by adding further information we can arrive at MWI. I plead guilty to failing to ask this question, note that shminux failed to volunteer the information, and finally plead that I think most RQMers would claim that theirs is an alternative to MWI.
MWI=universal state
Rovelli-rQM=no universal state
Can you describe in more detail what you mean by 'no universal state'?
By "state" I mean information physically embodied in a non relational way.
By "universal" I mean the maximal ensemble: universe, multiverse, cosmos, whatever.
(I think you might have been hearing "the universe does not have a state" as "nothing is real" or "nothing is out there". There is something out there, but it is not anything that can even be conceived as existing in a classical view-from nowhere style. "Following the idea of relational networks above, an RQM-oriented cosmology would have to account for the universe as a set of partial systems providing descriptions of one another. The exact nature of such a construction remains an open question."--WP)
To the extent that this seems to be meaningful at all, this would seem to imply that not only is the universe mysterious and ineffable, it's also uncomputable - since anything you can calculate in a turing machine (or even a few kinds of hypercomputers) can be "conceived of as existing in a classical view-from nowhere style" (it's just a list of memory states, together with the program). That's a lot of complexity just to be able to deny the idea of objective reality!
QM is computable. rQM doesnt change that. If an observer wants to do quantum cosmology, they can observe the universe, not from nowhere, but from their perspective, store observations and compute with them. Map-wise, nothing much has changed.
Territory-wise, it looks like the universe can't be a (classical) computer. Is that a problem?
As I understand it, any quantum computer can be modeled on a classical one, possibly with exponential slowdown.
"The universe is not anything that can even be conceived as existing in a classical view-from nowhere style" also means that the universe can't be modeled on a computer (classical or otherwise). From a complexity theory point of view, this makes the rQM cosmology an exceptionally bad one, since you must have to add something uncomputable to QM to make this true (if there is even any logical model that makes this true at all).
The fact that you can still computably model a specific observer's subjective perspective isn't really relevant.
Well, general relativity, while descriptively very simple, is awfully complex if you measure complexity by the length of a simulator program, so perhaps in the interest of consistency you should join the anti Einsteinian crank camp first.
Those incredibly successful theories were based entirely on the notion of complexity in a more abstract language where things like having no outside view and no absolute spacetime are simpler than having outside view.
Nice non-sequitor you've got there. Newtonian mechanics is simpler than general relativity. It also happens to be wrong, so there's no point going back to it. But GR is not even that complex relative to a theory that claims that the cosmos is an ineffable mystery - GR has well defined equations, and takes place in a fixed riemannian manifold. You can in fact freely talk about the objective spacetime location of events in GR, using whatever coordinate system you like. This is because it is a good theory.
Actually GR shows the advantage of having an outside view and being able to fit things into a comprehensive picture. If my graduate GR course had refused to talk about manifolds and tensors and insisted that you could only measure "lengths relative to specific observers", and shown us a bunch of arcane equations for converting measurements between different observers' realties, I imagine it wouldn't have been half as fun.
(Although the fact that certain solutions to the GR equations allow closed timelike curves and thereby certain kinds of hypercomputation is less than ideal -- hopefully future unified theories will conspire to eliminate such shenanigens.)
I think what EY is saying is that, rQM entails MWI, and only an extra layer of epistemological interpretation denies the reality to the worlds. ie, he thinks MWI says "QM implies many worlds" whereas rQM says "QM implies many worlds, but we should just ignore that". (One man's ontological minimalism is another man's epistemological maximism).
But that's all based on a sequence of misunderstanings. rQM doesn't allow observers to make contradictory observations AND there is no observer-indepenent world-state in rQM, so there are no multiple world-states in rQM.
So true.