[LINK] The Wrong Objections to the Many-Worlds Interpretation of Quantum Mechanics
Sean Carroll, physicist and proponent of Everettian Quantum Mechanics, has just posted a new article going over some of the common objections to EQM and why they are false. Of particular interest to us as rationalists:
Now, MWI certainly does predict the existence of a huge number of unobservable worlds. But it doesn’t postulate them. It derives them, from what it does postulate. And the actual postulates of the theory are quite simple indeed:
The world is described by a quantum state, which is an element of a kind of vector space known as Hilbert space.
The quantum state evolves through time in accordance with the Schrödinger equation, with some particular Hamiltonian.
That is, as they say, it. Notice you don’t see anything about worlds in there. The worlds are there whether you like it or not, sitting in Hilbert space, waiting to see whether they become actualized in the course of the evolution. Notice, also, that these postulates are eminently testable — indeed, even falsifiable! And once you make them (and you accept an appropriate “past hypothesis,” just as in statistical mechanics, and are considering a sufficiently richly-interacting system), the worlds happen automatically.
Given that, you can see why the objection is dispiritingly wrong-headed. You don’t hold it against a theory if it makes some predictions that can’t be tested. Every theory does that. You don’t object to general relativity because you can’t be absolutely sure that Einstein’s equation was holding true at some particular event a billion light years away. This distinction between what is postulated (which should be testable) and everything that is derived (which clearly need not be) seems pretty straightforward to me, but is a favorite thing for people to get confused about.
Very reminiscent of the quantum physics sequence here! I find that this distinction between number of entities and number of postulates is something that I need to remind people of all the time.
META: This is my first post; if I have done anything wrong, or could have done something better, please tell me!
I’d like to see the best anti-MWI/Everett article out there.
Here are the best items I have found in my search for anti-MWI reading. Some present anti-MWI arguments but in the end are pro-MWI.
David Wallace, The Emergent Multiverse (Pro; Anti-Everett arguments in the interludes)
Steven Weinberg: Lectures on Quantum Mechanics, sec. 3.7 (Seemingly pro-Everett, but in the end saying all current theories are flawed)
Adrian Kent, “Against Many-Worlds Interpretations” (Anti)
Stanford Encyclopedia of Philosophy “Many-Worlds Interpretation of Quantum Mechanics ” (Mostly Pro, Anti in sec.6)
Another relevant excerpt from the article:
It’s not clear that ‘MWI’ in the LW sense has very much content—in particular, it’s not clear that Eliezer is committed when he endorses MWI to Carroll’s description above. His recognition of the mysteriousness of ‘reality fluid’ and his willingness to entertain ideas like mangled worlds suggests he’s perfectly happy to modify QM to generate the Born probabilities, provided the modifications reflect the character of physical law better than Bohmian Mechanics and objective collapse do.
If MWI is just ‘Bohmian mechanics is wrong’ plus ‘objective collapse is wrong’ plus ‘the right answer will structurally resemble our current physics’, then the best articles criticizing MWI might be ones that defend Bohmian mechanics or an objective collapse theory as non-ridiculous, and argue that until we have a finished empirically adequate MWI we can’t be confident it will actually turn out simpler or more-in-the-character-of-physics than BM.
I think MWI means more than that. If you figure out how to ensure that Schroedinger’s cat is alive or dead, but not both, then it’s not MWI. The mangled worlds thing gets rid of some of the worlds, but it most certainly does not get rid of all but one.
Yes, those are all possibilities for what I am looking for. I’ll let the experts decide: I’ll be glad to read a coherent defense of Copenhagen, objective collapse, etc. or whatever it is that Hugh Everett/David Deutsch/Max Tegmark/Sean Carroll/etc are up against.
You may be interested in (if you haven’t already encountered) the “QBist” interpretation espoused by Fuchs, Mermin, Schack and others. Here are links to some appropriate papers by Fuchs, who in my opinion expresses the position most eloquently and efficiently:
http://arxiv.org/abs/1003.5209
http://arxiv.org/abs/1311.5253
http://arxiv.org/abs/quant-ph/0205039
I personally see QBism as quite a natural extension of classical Bayesianism to quantum mechanics, and I am surprised that it is not discussed at all in this community. Given the interest that Less Wrong members have in quantum theory and its foundations, I can only surmise that this niche is due to some kind of idolization of Eliezer and his views. I am somewhat placated by your inclusion of Kent’s paper in your list of coherent anti-MWI arguments, although I would love to see more of the genuine academic debate surrounding the interpretation and foundations of quantum theory faithfully reflected in this forum.
Just from reading the abstract, I’m not interested in an egocentric model of the universe. Ontology doesn’t follow the same rules as epistemology.
QBism is less an egocentric model of the universe, more an egocentric interpretation of quantum theory. It doesn’t say that we cannot have an ontological model of the universe; it says that quantum theory ain’t it.
However, I appreciate that this probably won’t help with your lack of interest. Best of luck with everything.
First, condescending snark? Seriously?
Second, now I’m really confused. In what way can’t QM be the fundamental ontology of the universe?
I’m not sure how to interpret your question.
If you’re asking:
“What is the case against the MWI interpretation of quantum theory?”
then I would probably cite difficulties in explaining why our branch’s history appears to be Born-rule typical as a major argument.
If instead you’re asking:
“What is the case for a non-ontological interpretation of the wavefunction?”
then the best I can do is attempt to summarise the arguments put forth in the above papers.
I meant the second. If that is the point of the papers, then I guess that’s fair enough, but, well, I don’t anticipate that their argument is going to be valid. I’ll go and read it; no need to summarize.
First paper,
I recognize that this is subjective and fuzzy, but… no? Bohm looks like an incredibly… well, I won’t get into that, but it doesn’t seem to me like a quick fix. Spontaneous collapse, okay, I grant that one. MWI doesn’t seem like a quick fix in any sense either.
No, that’s silly.
Yes, that was silly. But that’s hardly the strongest argument that could or has been made. You don’t get to pick your opponents’ arguments like that. The way Decision theory is used when I’ve seen it is: any structure which is formally equivalent to a decider is a decider, and QM has such structures.
… No, that’s stupid. No amount of sophistry can make predetermination relevant to the meaningfulness of ‘decision’. And of course the relevance of this argument is dependent on taking the argument for probability-in-MWI to be strictly dependent on the applicability of decision theory in a particular way which is not the way it’s actually being used. In particular, by the time you ascend the level of abstraction enough for decision theory to be relevant, you’re past the point at which predetermination has fallen away and you’re dealing with an effectively non-predetermined system.
And then he just goes off and makes an argument that the theory is information about the state, not the state itself. But… … … if it successfully models your information about a thing, then the thing acts consistently with the model, which means you’re also modeling the thing. There are theorems that constrain the ontology given these observations, and it basically boils down to ‘QM is super legit’.
I agree with you up until your last paragraph: the strength of Fuchs’ papers are not in their direct criticism of Everettian interpretations (Kent’s papers are a lot better at that).
For your last paragraph, I think Fuchs would take umbrage at the idea that you are necessarily “modeling the thing” when you assign a quantum state to a given system. I don’t think he believes that systems have a “true ontic state” of which quantum states are representative. Rather, the quantum state is merely a representation of an agent’s beliefs about the future outcomes of their interventions/measurements into the universe. Nevertheless, Fuchs claims to be a scientific realist.
I’m deliberately using the word “think” a lot here because I’m not confident of relaying Fuchs’ views faithfully (this isn’t directly my area of research). I haven’t adopted a QBist interpretation (or any other), but from what I’ve read I feel it’s worth serious discussion.
You also mentioned theorems constraining ontology. You may be interested in Fuchs’ take on Bell’s Theorem: http://arxiv.org/pdf/1311.5253v1.pdf . I have been to a talk where he explains why the PBR theorem doesn’t impact his interpretation, although the details evade me (and I can’t find anything written about it by him online).
I’m also a fan of the Bayesian interpretation of quantum mechanics (and I’ve said so here a couple of times). I try not to say ‘Quantum Bayesianism’, because it seems to me that Fuchs has run with that term in directions that I don’t necessarily want to go. (I’m an objective Bayesian, while Fuchs is a subjective Bayesian, and that’s just the start.) Some fans of Everett avoid the term ‘many worlds’ and cringe at some of the writings of David Deutsch, for similar reasons.
All of which is to say that if a hard-headed rationalist thinks that Fuchs is saying crazy things, run it against your model of a classical Bayesian saying similar things, and see if maybe it’s the interpretation of Bayesianism that you object to rather than the interpretation of quantum mechanics, and adjust accordingly. (Of course, this doesn’t help if you’re not a Bayesian in the first place, but Bayes is more sacred here than Everett.)
I don’t know whether I’d consider myself a “fan” of any particular interpretation, but I think Quantum Bayesianism ranks highly in terms of the insight it sheds into the nature of quantum theory. I’d be interested in discussing or reading about the Bayesian interpretation in more detail, as I haven’t had too much exposure besides Fuchs et al’s papers and a couple of conference talks. For example, what is your take on the recent PBR theorem concerning the ontology of the quantum state, and would this depend on whether your Bayesianism is objective or subjective?
Do you have any resources you’d particularly recommend?
My own brief summary of the subject is in an nLab article. (This is a math/physics wiki, and I assumed that the reader already knows quantum mechanics, at least up to the point of knowing what a density matrix is and what it’s good for.) There are references there, but you’ll notice that they’re all linked from the History section. (Part of the point of that section is to make it clear that the idea predates Caves, Fuchs, et al, although they certainly deserve credit for making it prominent.) I don’t know any over-all exposition that I really like, although I will always like the one cited as Baez 1993, which is where I learnt about it (and in fact where I first learnt about density matrices). That article doesn’t say ‘Bayesian’, but as I was already a Bayesian when I read it, and since I knew Baez to be a Bayesian, I naturally interpreted it so. If you interpret the probabilities in a different way, then you’ll get a very different interpretation of quantum mechanics as a result!
Someday I want to write something for beginners, at the level of Eliezer’s essays here (and in fact probably post it here too), but I haven’t done that yet! Until then, Baez’s piece is at the right level, but it doesn’t address the things that LessWrongers specifically would want to see.
I’d like to try and flesh out the difference between your personal interpretation and (for example) QBism. In your nLab article you describe an objective Bayesian is someone who “who naturally thinks of Bayesian probabilities as reflecting knowledge rather than belief, betting commitments, etc”. This suggests that it has to be knowledge about something; about some objective ontological process I assume. Is this ontological process still somehow “quantum” in nature? Is it perhaps a hidden variable of some kind? You didn’t reply to my previous question about the PBR theorem, which seems relevant since it places strong restrictions on hidden-variable-type psi-epistemic interpretations of quantum theory. I’d be very interested in hearing a response to that if you have the time.
Sorry, I forgot to answer you about PBR. I agree with Matt Leifer’s analysis. Briefly: it’s a fine theorem, and it’s good that they proved it, but it shouldn’t surprise anybody, and it doesn’t rule out any of the interpretations that people actually advocate.
As for my interpretation, I don’t have any problems with Caves, Fuchs, and Schack’s comprehensive 2001 paper on the subject (this is not their first 2001 paper, which was more about a technical result and vaguer on the interpretation). This paper writes extensively about states of knowledge. But since then, Fuchs has criticized that phrasing as insufficiently Bayesian (by which he really means insufficiently subjectivist). Quantum States: What the Hell Are They? at his website covers this, although it’s hard to read. As you can see from the dates, he had these thoughts pretty early on. Anyway, if the original 2001 papers define the orthodoxy for the Bayesian interpretation, then I am an orthodox quantum Bayesian, and Fuchs is the heretic.
Knowledge of what? Fuchs says knowledge of (or beliefs about, etc) the conesequences of one’s interventions in a system; one can also say (which may be same thing) knowledge of the outcomes of further measurements. I would use more realist language: knowledge of the physical observables. If you try to build an ontological model in which each observable has an associated actual value and the results of measurements are determined by these values, then you’ll have a hard time with that; but that’s not what I want to do. An observable O does not (necessarily) have an actual value, but it has potential values (comprising its spectrum), and I have knowledge about O that can be summarized as a probability distribution over these potential values.
To clarify: do you believe that there is something ontological in the system which is assigning probabilities of measurement outcomes in some way, when you make a measurement of the obervable O?
Probabilities aren’t ontological; they’re epistemological. I agree with everything that Eliezer writes about that, probabilities are in the map, etc.
But remove that word; there is something ontological that assigns measurement outcomes when I make a measurement. Or to keep it simpler: when I make a measurement, the measurement outcome is ontological.
A belated thank you for your replies. I feel like I’m starting to get the hang of what it means to take seriously the idea that probabilities are epistemological. It’s difficult, moving between papers espousing differing interpretations, because their very language tends to presuppose some ontological commitment or other.
There’s a set of subjective/irrealist interpretations as well, which are routinely ignored here. Noticeably, Copenhagen is one such , but is constantly conflated with objective collapse here.
EY is sold on Deutschs presentation of MWI, which presents it as a kind of plain, unvarnished interpretation … but that isn’t a fact.. Others see MWI as making posits: that the wave function is, that there is state, that there is universal state, that there is a universal basis...
That’s a good point; would anyone be interested in a follow-up sequence to the quantum physics sequence that presents arguments on all sides equally (at least, as equally as a biased individual can present them)? Eliezer sort of set up many worlds as the obvious hero and the Copenhagen interpretation as a weak enemy; there are more modern interpretations such as Quantum Bayesianism and pilot wave theory that are harder to dispel.
Instructions for polls are here: http://wiki.lesswrong.com/wiki/Comment_formatting#Polls. In the mean time, I’ll get this one for you.
Would anyone be interested in a follow-up sequence to the quantum physics sequence that presents arguments on all sides equally?
[pollid:823]
Yes, contingent on finding a good author.
Also, note that this poll is subject to heavy selection pressure based on who read the comments on this article.
It doesn’t have to be one contributor, N authors could put the case for N alternatives to MWI.
Assuming that the question means “would you be interested” and not “does there exist at least one person in the multiverse who would be interested”.
Yes, let’s assume that.
:|
I’d be even more glad to read an article that specifically is against MWI/Everrett (or whatever you call it).
David Wallace, The Emergent Multiverse, Interludes I and II, presents both sides but in the end is pro-MWI.
A coherent, intelligent, reasonable article by an advocate of the other side would make things clearer.
Thanks, I completely forgot polls were a thing one could do.
While I agree, we shouldn’t expect there to be any ‘the’ best anti-Everett article. There are any number of non-Everett positions, and they all disagree with Everett for different reasons. What we need are multiple articles putting forth the best arguments for various positions (or one large article with multiple sections).
ETA: The main thing that this site really needs is just awareness that there is more to consider than MWI and objective collapse. I agree with Eliezer’s arguments that MWI wipes the floor with objective collapse. That doesn’t make me accept MWI, however. (Eliezer does do a short survey of other interpretations, but none of the ones that I think are worth consideration, besides Bohm’s, show up.)
I like this
That isn’t an argument against MWI/Everett, it’s an argument against thinking about quantum computation as “computing 2^n values of f(x) in parallel in different worlds”. (On the grounds that what licences us to consider two Everett branches as separate “worlds” is that decoherence makes their interactions negligible, while what happens in quantum computation is all coherent and preventing decoherence is a central engineering problem. [EDITED to add: And that the operation of a “cluster state quantum computer” is not helpfully thought of in terms of doing lots of computations in parallel. I don’t know enough about the cluster state model of quantum computation to have any idea how strong that argument is.])
The comments below the article evoke my “Read the Sequences” emotions.
But where are those other universes?
Doesn’t splitting the universe by making a decision contradict the conservation of energy?
And I feel like: “The conservation of energy is a rule within the universe; it does not apply to splitting universes. Even the notion of ‘where’ only applies within the universe. And the universe does not split ‘when you make a decision’; it keeps splitting all the time regardless of the content of your neurons. Duh! Could we just skip this level of debate and give more space to meaningful comments, please?”
But then I realize that’s me, spoiled by reading the Sequences. For most readers those questions probably feel completely relevant, and they would wonder if no one would mention such obvious objections.
Going a bit more meta—because I really don’t care about the quantum physics that much—this seems like a problem of debates in general. You can’t have a debate on different levels of expertise simultaneously. Bad arguments drive out the good ones. The easiest way to protect the good arguments is to forbid the bad ones; but again, to an outsider this will seem like those bad arguments are actually the good ones you don’t have an answer to! Or maybe there could be multiple “levels” of the debate where moderators could move individual comments to a “beginner” or “expert” column. (Any question that was already answered on the website and does not bring any new argument is classified as “beginner”.)
Also I realize that if I had a blog with discussions below the articles, this (having to answer to the same trivial objections again, and again, and again) might drive me crazy. But that’s a fact about me.
One way of interpreting the math is even more basic: from the perspective of conservation of energy, there’s still just one universe with different parts of the wave function not interacting.
I’ve daydreamed about debate clubs using kyu/dan levels like in go, but I don’t think that would go over well with the majority of people. I think it would turn debating into a competition to memorize “standard” lines of argument so you can pass tests without actually understanding them fully. I can dream, though...
I have commented there, and I will quote my comment here. To clarify, I am not anti-MWI, I am pro- experimental evidence.
It seems to me that you strawman a bit the main objection. Indeed, as you say
However, this does not answer the objection that
if you phrase it the way the MWI opponents usually mean it:
or than any other interpretation favored by a particular MWI opponent, as long as that interpretation makes exact same predictions as the orthodox QM.
You are certainly right, MWI does not need an extra collapse postulate, it comes out in many possible ways from using the L^2 norm for probability in conjunction with, say, unitarity, or some other equivalent experimentally justified assumption.
Unfortunately your “rightness” is rather hollow, because you still have no definitive experiment that would convince your opponent. And so the argument becomes philosophical rather than physical, as it cannot be resolved by the scientific method.
Needless to say, a QM formulation which would lead to a testable prediction beyond those derivable from the orthodox approach, would be an exceedingly big deal. But one can hope.
He asserts that such an experiment exists. I would love it if he were to expand on this assertion.
I don’t have the expertise to evaluate it, but Brian Greene suggests this experiment.
That experiment sounds very problematic to me. He says “After you measure the electron’s spin about the x-axis, have someone fully reverse the physical evolution.… Such reversal would be applied to everything: the electron, the equipment, and anything else that’s part of the experiment.”.
There is no explanation of the mechanics of how he thinks such a time-reversal could be implemented. We simply don’t have the fine control over the quantum state of the entire measurement apparatus. In fact, the very assumption that quantum theory is even the true/applicable state of affairs at this macro scale is the kind of thing that many Copenhagenists dispute.
Conversely, if it were possible to have such a fine control over the entire system including the very equipment used to perform the measurement, well then, you might as well simply make a quantum measurement of the larger quantum system which includes that apparatus! There would be different outcomes depending on whether collapse has or has not yet occured.
It seems like whether or not this experiment even makes sense relies somewhat on whether MWI is true. Ultimately I think the very description of this experiment makes hidden assumptions, which beg the same question it is trying to answer.
Yes, dynamical collapse appears to make new falsifiable predictions. MWI doesn’t, unless you take Deutsch’s reversible quantum consciousness seriously.
And even if you do, then the only viewpoint you will have really falsified is one which postulates that (a) the state vector collapse is caused by consciousness, and (b) concludes that therefore any consciousness has to do the trick, even one simulated on a quantum computer. I have met exactly zero physicists who’d treat (a) seriously, but even if you believe in (a), (b) still doesn’t need to follow (someone could believe that only real human brain makes the magic happen).
(I assume you were referring to experiment 3. from Deutsch’s “Three experimental implications of the Everett interpretation in Quantum Concepts in Space and Time.”)
Thanks for the reply; I will most likely be writing a longer, not-just-a-link post on some aspects of the argument that to my knowledge were not covered on Less Wrong. Namely, the experiments by David Deutsch which can distinguish between EQM and the Copenhagen Interpretation (but require quantum computers to get much, much better before we can test them), as well as arguments brought up by Sean Carroll and Scott Aaronson.
As for your argument, the idea there aren’t many worlds requires an extra collapse postulate, so many worlds is the default interpretation of quantum mechanics. The shut-up-and-calculate interpretation is just a refusal to accept any ontology whatsoever.
I could easily turn it around and say;
CI is no more testable than shut-up-and-calculate-only-probabilities-are-real, or than any other interpretation favored by a particular CI opponent, as long as that interpretation makes the exact same predictions as the orthodox QM.
Since MWI and CI are on equal footing in that respect, and MWI has one less postulate, I think CI should be classified as a fringe position and everyone should provisionally accept MWI, unless they are a particularly dead-set on refusing any ontology at all. Of course, once we are capable of putting entire minds into superpositions we can just test it and find out once and for all.
That follows if you make two assumptions that are standard in the Sequences, but not elsewhere. One is that the Copenhagen Interpretation is the one that says collapse is a real physical process. Another is that MWI is the only non collapse theory.
Are you arguing that it isn’t?
Yes
From wikipedia :
According to Howard, wave function collapse is not mentioned in the writings of Bohr.[4]Some argue that the concept of the collapse of a “real” wave function was introduced by Heisenberg and later developed by John von Neumann in 1932.[23] However, Heisenberg spoke of the wavefunction as representing available knowledge of a system, and did not use the term “collapse” per se, but instead termed it “reduction” of the wavefunction to a new state representing the change in available knowledge which occurs once a particular phenomenon is registered by the apparatus (often called “measurement”).[24]
Note also that the objective function theories were put forward as novel theories, by people who were familiar with content of CI, at a much later period than the Bohr-Heisenberg discussions: the Penrose interpretation dates to the late 90s, GRW from 1985.
So the collapse only exists in straw-Copenhagen? Or is it yet another scientific theory that popularly gets mistaken for Copenhagen interpretation?
The CI was somewhat minimal interpretation, that posits some sort of transition between the quantum realm and classical information during measurement, but says little about its nature. That left the field open for other interpretations to be more specific about collapse/projection/measurement, variously portraying it as objective, subjective, actually decoherence, etc.
If you have realism about the evolution of state according to the Schroedinger equation, then you need an extra collapse postulate to avoid many worlds.. But you don’t have to have realism about state, so there are ways of avoiding many worlds without introducing collapse.
It would be very helpful if you would spell out these initialisms/acronyms.
Edited.
Sorry, you are missing the point. Yes, MWI uses rather more natural assumptions than collapse to get to the same result. Yes, the ontological argument started by EPR and continued by Bell, Everett and Deutsch lead to a lot of progress in understanding what can or cannot lie behind the 90 years-old math of QM. No, you don’t get to denigrate one model you don’t like if it gives you exact same predictions, even if some very high-status people you trust do so.
Parroting Eliezer does not make you smarter.
I’m not parroting Eliezer, I’m a physics grad student who happens to have agreed with the many worlds interpretation even before I found Less Wrong. Nor am I denigrating one model because I don’t like it. Even if the models were on equal footing with regards to experimental evidence, MWI has fewer postulates and is therefore the more likely theory. You seem to agree that MWI has fewer postulates, so given a choice between the two, why favor the collapse interpretation, or refuse to give any interpretation at all?
EDIT: I hope I don’t sound flippant with my response, though your ad hominem was unwarranted. I do understand that my arguments are basically the same as Eliezers, since they’re the low-hanging fruit on the tree of pro-many-worlds arguments, so I will give you that I do sound like an Eliezer-parrot even if I don’t intend to. With that, think you’re right that Less Wrong’s arguments are sub par, and I’m going to try to write a few posts that present all the sides as equally as I can manage.
Apologies, you did not sound to me like a physics grad student when you said “CI should be classified as a fringe position and everyone should provisionally accept MWI”. (And “ad hominem” does not mean an insult, it means “I reject your logic based on who you are, rather than on what you say”.)
This is the crux of the issue. What do you gain by favoring one over another? My original point was that there is little to be gained
I understand the Deutsch’s logic “but if only we had a reversible and “conscious” quantum computation, we could test it”, which assumes that we know what conscious means and whether it can be reversible, tying one difficult issue to another just as deep. Until the latter is resolved, the former is not really testable.
I suppose one would only gain a simpler theory, since both theories predict the same thing. So from the perspective of neatness, I’d prefer to have one less postulate. From the persepctive of actually solving problems, none of this matters.
In fact, none of my professors throughout college ever brought up the topic of interpretation, except to say that it was complicated. I suppose that’s why I don’t sound like a grad student to you; though I can solve problems very well, everything I know about the interpretations of the theory I have gleaned from textbooks and the internet; I have yet to look at specific papers, or study it in depth.
Part of the reason I want to write more on this is to have an excuse to force myself to learn/study more on the issue; it is still possible to change my mind, after all.
Though on the issue of reversibility; if we accept the mind is capable of being simulated by a computer, and we had a computer that was made of Toffoli gates (or the quantum version, if such a thing exists), would that mind not then be reversible?
And thanks for pointing out my error on the use of ad hominem; I always forget that.
Right.
I was in the same boat, having gone through all the undergrad and grad quantum courses without learning anything about ontology, except for the general unease with the Born postulate. This is a common situation. Only Quantum Information courses are sometimes different. And philosophy of physics, but I don’t take those seriously.
By all means, just make sure you don’t have a “favored interpretation” when you start, it will bias you without you noticing.
There are arguments that dissipation and irreversibility is essential for consciousness. Whether they are any good will depend on what consciousness is. At this point we have very little to go on beyond “hopefully it can be simulated some day”.
The results of that are kinda noticeable,
I don’t see why “fewer postulates” makes something “more likely”. Occam’s Razor is not a natural law, it’s a convenient heuristic for human minds.
“For every complex problem there is an answer that is clear, simple, and wrong.”—H. L. Mencken
If I explain a phenomenon using 10 postulates (of some fixed length) and you explain it using 10,000,000,000, your theory gets demoted (even if we don’t know anything else about the two theories) because it has more ways to go wrong. If you accept that this is true in a big way in the extreme case, you should accept that it is true in a small way in more mild cases (e.g., 10 postulates vs. 20, or 10 postulates vs. 100).
I like to think of it as an extension of the conjunction fallacy; the probability of A and B being true can’t be higher than the probability of either A or B; adding new conditions can only make the probability stay the same or go down. So the probability of a theory once it has an extra postulate, must be equal to or lower than the probability of the same theory with fewer postulates. Of course, that assumes the independence of the postulates.
The probability of the postulates all being true goes down as you add postulates. The probability of the theory being correct given the postulates may go up.
This assumes the postulates are interdependent such that the theory may be true with all postulates, but false with all postulates save one. In this case, the theories are the same except for the collapse postulate, which may or may not have any real-world consequences, depending on whether you believe decoherence accounts for the appearance of collapse all by itself.
Not only it assumes independence, it also assumes that the two competing theories have exactly the same postulates except for a single extra one. That is typically not how things work in real life.
Er, no it doesn’t. Where are you getting this?
From here:
Among theories that explain the evidence equally well, those with fewer postulates are more probable. This is a strict conclusion of information theory. Further, we can trade explanatory power for theoretical complexity in a well-defined way: minimum message length. Occam’s Razor is not just “a convenient heuristic.”
Could you demonstrate this, please?
The linked Wikipedia page provides a succinct derivation from Shannon and Bayes’ Theorem.
Heh. I think you’re trying to generalize a narrow result way too much. Especially when we are not talking about compression ratios, but things like “explanatory power” which is quite different from getting to the shortest bit string.
Let’s take a real example which was discussed on the LW recently: the heliocentrism debates in Renaissance Europe, for example between Copernicus and Kepler, pre-Galileo (see e.g. here). Show me how the MML theory is relevant to this choice between two competing theories.
Kepler’s heliocentric theory is a direct result of Newtonian mechanics and gravitation, equations which can be encoded very simply and require few parameters to achieve accurate predictions for the planetary orbits. Copernicus’ theory improved over Ptolemy’s geocentric theory by using the same basic model for all the planetary orbits (instead of a different model for each) and naturally handling the appearance of retrograde motion. However, it still required numerous epicycles in order to make accurate predictions, because Copernicus constrained the theory to use only perfect circular motion. Allowing elliptical motion would have made the basic model slightly more complex, but would have drastically reduced the amount of necessary parameters and corrections. That’s exactly the tradeoff described by MML.
Not for Kepler who lived about a century before Newton.
My question was about the Copernicus—Kepler debates and Newtonian mechanics were quite unknown at that point.
Even Kepler’s theory expressed as his three separate laws is much simpler than a theory with dozens of epicycle.
The dozens of epicycles aren’t on a par with Kepler’s laws. “Planets move in circles plus epicycles” is what you have to compare with Kepler’s laws. “Such-and-such a planet moves in such-and-such a circle plus such-and-such epicycles” is parallel not to Kepler’s laws themselves but to “Such-and-such a planet moves in such-and-such an ellipse, apart from such-and-such further corrections”. If some epicycles are needed in the first case, but no corrections in the second, then Kepler wins. If you need to add corrections to the Keplerian model, either might come out ahead.
(Why would you need corrections in the Keplerian model? Inaccurate observations. Gravitational influences of one planet on another—this is how Neptune was discovered.)
I have heard that Copernican astronomy (circles centred on the sun, plus corrections) ended up needing more epicycles than Ptolemaic (circles centred on the earth, plus corrections) for reasons I don’t know. I think Kepler’s system needed much less correction, but don’t know the details.
Who told you that? Your philosophy of anti realism and pro empiricism is still a philosophy.
While I disagree with shminux’s views on the issue, I should like to note that these are astonishingly poor grounds on which to attack those views. First of all, your argument falls prey to the tu quoque fallacy. Second, it is almost certainly true that certain philosophies are better than others when it comes to understanding the world around us, and empiricism is one of the best IMO, practicalities notwithstanding. Saying “your view is also a philosophy” doesn’t prove anything. See the fallacy of grey.
I dont see how.
Empiricism has to be the one and only philosophy for shmimuxs claim to go through. Even a second best philosophy could be used to “denigrate” one theory as compared to another, empirically equivalent one.
Note that philosophies emphasizing empiricism famously have problems with self justification, eg L.P..
Saying yay, empiricism! doesn’t resolve those issues.
Shminux is (seemingly) criticizing non-empirical discussion and, by extension, most of philosophy. You responded that he/she is still espousing a philosophy: empiricism. This statement, whether true or not, has no bearing on the validity of his/her argument; instead, it is simply saying, “Well, if philosophizing is a crime, you’re doing it too, you hypocrite!”, ignoring the fact that if philosophizing is bad, it doesn’t matter if shminux is doing it or not. (Likewise if philosophizing is good.)
This is true, which is part of the reason I said I disagreed with shminux. That being said, your original objection was that his “anti-realism was still a philosophy”, which didn’t really bring up that particular point.
That’s because the justifications have typically been of the armchair variety. Of course you won’t be able to come up with a justification for, of all things, empiricism just by sitting there and thinking. Empiricism, however, is easily justified if you look at it empirically: empirical studies work, as shown empirically by the tremendous success of science in predicting observations. I’d say that’s pretty good as justifications go, no?
The point is not whether philosophy is morally bad or good, but whether it is epistemically bad or good. Shmimux has not provided an empirical justification for empiricism, and cannot consistently provide any other.
Please publish that result. Lots of things are claimed to work, and formalising handwaving claims of “working”, so they are not a free-for-all has proven extremely difficult.
Note that pragmatism, the fullest exploration of the “it works” philosophy to date, was intentionally inclusive.
There’s no “claim”. If you take the advice of doctors, use modern technology, or pretty much anything that relies on a scientific understanding of the world around us, you are implicitly endorsing empiricism as the philosophy that made it all possible.
You have missed the point. For any kind of “woo” , there are people who claims it works..
I… really don’t see how this has anything to do with the discussion, unless you’re calling science woo.
...Are you calling science woo?
I am saying that to demarcate woo from non-woo using the criterion of “working” you need a criterion of working that isn’ta subjective gut feeling. You need to solve the problem of formalising the empirical justification of empiricism.
All right. How about this: something “works” if it is independently replicable and reliably results in statistically significant deviations from the null result.
Reliable results of what? Is there anything that reliably indicates realism? If someone says that your reliable resultsare just accurate predictions of subjective experience, how do you counter them? And does your method tell you what you should be doing , or just what experiences to passively expect?
Isn’t it circular reasoning to justify empricism on the grounds that it works empirically?
I enthusiastically endorse realism about ants.
If your argument can be resolved by the scientific method, then why even bother arguing? You’re often not that lucky. Should the government be bigger or smaller? In principle, you could randomly sort the 50 states into three groups where you increase the budget of one, decrease the budget of another, and leave the last as a control, but nobody’s going to do that.
To come up with an argument which can be tested experimentally. At least in physics, which is the subject area here.
Alas.
Ah, but there are other ways. There are 200 other countries in the world, and some come very close to the experiments you want to perform, now or in the past. Does gun control reduce crime? Tested. Does universal healthcare reduce medical expenditures? Tested. Does changing attitudes toward women in STEM improve the fraction of exceptional women scientists? Tested. Does decriminalizing marijuana lead to more drug use? Tested.
You can argue about these issues with all the Bayesian might until cows come home, it is no substitute for a good experiment.
They let you look for correlations. They don’t let you run a good experiment. People can come up with theories that explain the facts, just as MWI and the Copenhagen Interpretation explain the facts. Science won’t save us here.
To which the answer is “its not a theory , its an interpretation. Interpretations arent testable, they’re philosophy. Including anti realism”.
Some people will vote you down for posting something that’s mostly just a link. Personally, I like good, relevant links.
How did you post this so as not to display its vote total?
Votes are displayed only after a post is an hour or so old. Not sure what the actual value is. They are still shown on the sidebar.
My understanding is that new posts don’t show their vote totals right away, to help prevent snowball effects.
A link with an example from the article is much better than mere link. It gives you a good estimate of whether you want to read the article before you click the link.
Can anybody point me to what choice of interpretation changes? From what I understand it is an interpretation, so there is no difference in what Copenhagen/MWI predict and falsification isn’t possible. But for some reason MWI seems to be highly esteemed in LW—why?
Because Copenhagen introduces additional rules that act in ways counter to everything we know about physics and gives no experimental evidence to justify them.
Where Copenhagen means “Objective Reduction”
What does this mean?
Mostly because Eliezer wrote a number of highly emotional and convincing posts about it.
Just to be clear, do these multiple-universes have the same qualities as the universe that we inhabit?
Yes. It’s possible that the vast majority of them have no life and we’re in this one because of the anthropic principle, but beyond that they all act the same.