How Many Worlds?
How many universes “branch off” from a “quantum event”, and in how many of them is the cat dead vs alive, and what about non-50/50 scenarios, and please answer so that a physics dummy can maybe kind of understand?
(Is it just 1 with the live cat and 1 with the dead one?)
How many ink blots are in this picture ?
For “many worlds”, imagine that evolving in time, with fuzzy borders.
The Many Worlds Interpretation doesn’t imply a countable number of worlds that suddenly branch, it’s more like a fuzzy continuum; talking of branching worlds and timelines is just a high-level abstraction that makes things easier to discuss.
This is a really good analogy to explain what a wrong question is.
It rather seems to me an imprecise analogy which makes thinks harder to discuss. But I agree with the general sentiment.
Not countable many, but continuum many? Is that what you say?
Maybe—I’m not sure of what you mean by “continuum many”—you mean like real numbers? I was thinking more of something like “roughly countable, though the count will depend on which definition of “world” (or “blob”) you use”, or even better, “it doesn’t really matter”.
Yes, I mean as many as real numbers. Or maybe even more, I don’t know. I am asking you, who is telling us that:
(Of course, MWI is popular, but I agree with those who say—it’s just ridiculous.)
Thanks for answering!
I guess I was confused by this:
That is a somewhat useful analogy, but it can be taken too far. But it seems to me to be saying the same thing (though perhaps not as clearly) as the inkblot above:
Can you really count it? Not really!
I thought that when it said “At the beginning there is one blob, at the end there are two blobs” it was saying that the “worlds” did eventually become discrete, you just couldn’t tell exactly when.
When you mix regions of stability and chaos, eventually things settle down into relatively discrete zones… along some directions… while being smeared out all over the place in others.
Edited to add: Are these downvotes from people who know quantum mechanics or dynamics in phase space, or is my comment just making people confused again (a bad thing to be sure), or what? I can probably fix it, but it’d be best to know what about it needs fixing.
No idea why whoever downvoted you did so, but here’s why I think I felt your comment was not useful to me, or much less useful of what it could have been if you happen to know what you’re talking about (I don’t so I can’t tell):
Your statement states a fact without any explanation, examples or pointers to such. If you had said something like “When you mix regions of stability and chaos, things never settle down into discrete zones… it’s all smeared out all over the place.” — then the effect of reading it would pretty much have been the same unless I already knew about the subject enough not to need your comment.
Imagine someone not having any education in astronomy saying something like “I thought the sun and stars turn around the Earth”, and you commenting “Actually, the Earth spins around itself, and it turns around the sun, while the other stars pretty much go every which way.” Unless the first person knew you were a good astronomer, they don’t really learn anything. And even if they did believe you knew you to be an expert on what you were talking about, they might learn it as a rote fact, but won’t really understand much.
Oi, if that’s the problem I’ll just call a halt. Chaos theory is kind of like quantum mechanics: done right, it’s tough, and done easy, comes out horribly wrong.
So… your comment was an attempt at “done easy”, or was it “tough”?
(It occurs to me that the line above would be normally interpreted as snarky. My intent was half friendly joke, half “if you have that opinion about Chaos theory, what did you try to achieve in your earlier comment?” I just don’t know how to express that in written English...)
So the key idea is that of “Hilbert space,” which is a way to describe the universe named after a guy called Hilbert.
So for example if I flip a fair quantum coin, it’s 0.5 heads and 0.5 tails. “Heads” and “tails” here are actually dimensions, like x and y, in Hilbert space, and the universe is at the point (0.5, 0.5). If the coin wasn’t fair, then the universe could be at the point (0.6, 0.4) or even (0.999, 0.001). The number of dimensions didn’t change, because there’s still just heads and tails, but the point that represents our universe changed.
When you look at the coin, the universe collapses to two possible points: (0,1) and (1,0). The coin is either heads or tails. This corresponds to two “worlds.” It doesn’t matter whether, previously, your description was fair or not—the coin is still either heads or tails, so there are two worlds. Though I suppose if your previous description was (1,0) - definitely heads—you wouldn’t assign any probability to it being tails, so there would only one “world”.
Of course, it can get much more complicated. If you roll a quantum d20 instead of flipping a coin, you have to assign a point with 20 coordinates: (0.05,0.05,0.05,0.05,0.05,0.05, 0.05,0.05,0.05,0.05,0.05,0.05, 0.05,0.05,0.05,0.05,0.05,0.05,0.05,0.05). And if you throw a dart at a continuous dartboard, you have to assign a value to an infinite number of points! But don’t worry—that’s just the same as a function, like x^2 or sin(x). But if you throw a dart at a dartboard, does that mean you just split off an infinite number of worlds? If you flip a coin, and then throw the dart, is that 2*infinity = infinity?
So basically, when there are lots of possible outcomes the idea of “worlds” becomes not so useful.
Although this gives the correct answer as far as the number of worlds is concerned, it sounds strange within the MWI (which was supposedly assumed in the original question).
I think you can’t do MWI justice without introducing the observer in the game: apart from the coin which lives in a two-dimensional universe, there is the observer whose mental state lives in a (at least) three-dimensional universe. The dimensions of the observer’s mind are “think the coin landed heads (TH)”, “think the coin landed tails (TT)” and “don’t know (DN)”. Together we have six dimensions, all combinations of coin and observer states:
coin:heads, observer:TH
coin:heads, observer:TT
coin:heads, observer:DN
coin:tails, observer:TH
coin:tails, observer:TT
coin:tails, observer:DN
In this space there are three planes defined by the observer’s mental states: for example, the plane TT consists of vectors that have all coordinates except the second and fifth equal to zero. The observer’s consciousness has a peculiar property of seeing only projections to these planes. Those projections are what is called worlds.
In the beginning, the observer doesn’t know and the coin is 50% heads and 50% tails; this means the state vector of our model “universe” is (0, 0, 0.707, 0, 0, 0.707). (Have I mentioned that the probabilities aren’t in fact the coordinates but their squares? Anyway, this is a technicality we don’t really need now, but we should be consistent. The state vector must have lenght precisely 1.) At this moment, the projections to the aforementioned planes are
DN: (0, 0, 0.707, 0, 0, 0.707)
TH: (0, 0, 0, 0, 0, 0)
TT: (0, 0, 0, 0, 0, 0)
In a sense, three “worlds” already exist, but since two of them have zero length, they can be disregarded.
Now the observer measures (looks at) the coin. Measurements are mysterious processes which, over some time, get the observer into correlation with the coin. The universe state vector becomes (0.707, 0, 0, 0, 0.707, 0) and the projections are now
DN: (0, 0, 0, 0, 0, 0)
TH: (0.707, 0, 0, 0, 0, 0)
TT: (0, 0, 0, 0, 0.707, 0)
Now we have two non-zero projections and can speak about two worlds. But remember, there is still only one six-dimensional Hilbert space with one universe state vector. It is believed that under normal circumstances no processes can put the state vector back to the state where there are less non-zero projections than before. But in principle it could happen and if it does, the worlds would merge again.
Congratulations, you just earned yourself one “click.” I’ve never really gotten quantum physics, not that I’ve tried much. But your description as a Hilbert space makes a lot of sense to me. It also helps me understand why “decomposing the wavefunction” is important or even necessary as a concept.
Here I predicted that a question like this one about quantum physics would get voted up, even though a similar question on classical physics got voted down. Currently I’m wrong, but only just.
See section 6 of this David Wallace paper.
I’m surprised that this has not been said, so I’ll present the way I think about branching, though it will be a bit heavy on the mathematics and I apologize for that. Perhaps someone else can pare it down a bit. Also, I am not a physicist, I am a mathematician, so my model is probably more optimized for making me feel like quantum mechanics describes a world in the abstract, and less optimized for describing the specific world we live in.
In the Schrodinger’s cat experiment, we have a vast number of elementary objects, which are essentially all wave functions. If we consider the reduced density matrices, the set of all possible reduced density matrices is… well naively I might guess that it is the n^2-fold product of the unit interval, where n is the dimension of the matrix, but it’s also possible that the space of reduced density matrices is some other lie group (if it turns out the space is NOT a lie group, this interpretation is in serious trouble!). Either way, there is a Haar measure on it; which is to say we can, in some sense, have a continuous space of all the elements of that group. Now conceptually I’ll consider each of the coefficients of these matrices as sort of like a probability. Now I construct one universe for every member of the direct product (maybe direct sum?) of the group, indexed by the set of wave functions in my experiment, and I call this set of universes the “branches which causally descend from my circumstance” because that sentence makes me feel warm and fuzzy. In each of those universes, each wave function expresses itself as though it collapsed in one direction if the coefficients of the matrix indexed by that wave function are greater than the reduced density matrix of that wave function, and the other if they are less. The fact that I don’t know what should happen if the coefficients are equal bothers me, but this isn’t really a good expression of the “directions” that a matrix can “collapse in” so I will guess that there is a better formulation that a physicist could make that resolves this issue, and if I am convinced there isn’t, I’ll start reading up on quantum physics for the purpose of sleeping better at night.
The naive picture that I had that I tried to comb out into a real model here is that there are a bunch of continuous probabilities (intervals [0,1]) which resolve as either 0 or 1. So the number of universes coming out should be indexed by intervals [0,1] for every probability in the situation, with that universe coming out with a 0 if the value in the index is less than the probability and a 1 if it is greater. I suppose, since the big deal here is measure, that you could arbitrarily assign the equality case here to either side and it would never make a difference.
I’ll reiterate at this point that I’m a mathematician, not a physicist. This is what’s gone on in my head as an explanation for what it REALLY MEANS to have many worlds. I would love to hear a physicist’s perspective on why this is all complete nonsense.
The number of possible outcomes you are able to distinguish. For the cat, if the only information you get is dead/alive, two. If the probabilities aren’t 50⁄50, you can think of one of those branches as stronger.
(Edited several times, this is the final version, I hope.)
Uncountably many. Consider that on the scale of the Omniverse (which contains only this one particular universe among uncountably many) the probability for any event is 1. It is also so, because it is absurd to suppose there is a universe in which something, if there be anything, does not exist. Furthermore, even if the probability for an event in our universe were 0 that would in no way serve as an impediment to its occurring in the long run.
I read your post in the other thread by Mitch_Porter, asking about why your post here got downvoted. As someone who would also have responded with the answer “uncountably many” and was in fact surprised to find that that wasn’t quickly established as the obvious correct answer, I thought I might come take a look.
I would guess that the (mild) downvoting on this post comes from the fact that after your first sentence, you stop talking about specific instances of decoherence and start talking about omniverses and probabilities of 1 and 0. your language is more technical than it needs to be and grammatically odd.
all of these fragments make me cringe and have to parse what you’re saying.
I hope this helps!
Yes, it does. Thanks. I suppose I should lower my expectations of the general community’s familiarity with “technical” subjects.
The way I would phrase this is lowering your expectations of the community’s willingness to wade through jargon and derogatory language. It isn’t that people won’t understand, it’s that they won’t want to read the comment.
Point specifically to that which is “derogatory” in the initial post. I don’t participate in LW to get upvoted, anyway, since that is merely a marker of groupthink (or correlates in assigning yay or boo ascriptions to a particular post for mere classical conditioning to take place). I didn’t use any jargon except the term “omniverse” which anyone equipped with Google could look up themselves. I suppose when writing comments on LW, in special cases (as in a technical topic), one must hold the hand of the reader, lest they become enraged by subtleties and novel syntactical arrangements of words.
The part where you say “it is absurd to suppose” when it isn’t made clear in plain English what it is that is absurd. However I mostly included the statement about derogatory comments in reference to your other comments.
Perhaps a better term than “technical jargon” would be “convoluted grammar.” I pointed out specific examples of phrasing I found unpleasant to read in my original reply.
Also someone else may have pointed this out but the general policy on lesswrong is not to vote on agree/disagree but on this comment was worth reading/was not worth reading. Saying you are not interested in upvotes is essentially saying you are not interested in contributing to the community. If you don’t want to explain yourself in a friendly and accessible way then you have no obligation to, but I think you will be the one who misses out.
No one “pointed this out” to me. But they did downvote whatever I said, without so much as a reasoned explanation. I seriously doubt that that is the actual universal employment of the voting mechanism, particularly since I’ve seen quite a few good posts on LW with numerous down-votes accorded to them. Perhaps my standards of “worthwhile reading” are too generous for the likes of LW’ers.
No, I disagree that that is what I’m saying about the nature of not being interested in up-votes. I can still contribute without being up-voted, and I’m fine with that.
My grammar may be “convoluted” to those who do not take a liking to heady material (yes, I read difficult stuff all the time), so I can’t be blamed for slipping into what I find most comfortable, just as you do without any second thought.
The answer is only true if the measured quantity has continuous spectrum, therefore not applying to the only explicitly mentioned example of the cat. Furthermore I don’t follow your subsequent reasoning.
Taking the universe as a QM event most definitely implies there are uncountably many universes. The OP very clearly asked for non-standard instances of the question, and a generalization of the question most certainly applies thereto.
I certainly hope others do not continue to down-vote what they don’t grasp, because LW will only be the worse off for it. (Not implying you down-voted, but if you weren’t, then the one who did obviously hasn’t the wherewithal to state an outright objection.)
Edit: if you don’t “follow”, at least state in what exactly you don’t follow so that I can actually provide something to your explicit satisfaction.
I was the first person to downvote. Not because I don’t grasp, but because I believe your explanation is in the best too brief to be generally intelligible. My negative opinion can be, of course, due to my stupidity, but as for my downvoting strategy, my own judgment is all I can rely upon. (My judgment also tells me that you appear a bit oversensitive to downvoting.)
From the former comment:
I don’t see how it is relevant. Quantum branching doesn’t require Omniverse. That alone makes your argument seemingly irrelevant. But let’s proceed.
I have no clear idea what a probability of event happening in the Omniverse means. Could you elaborate? (Possible issues: From an observer-independent point of view, the event either happens or not. The observers are restricted to their own universes, how do they construct probabilities over events in different universes? If the generic word “event” is replaced by the actual specification of the event, is the number of universe included—i.e. do you replace it by “two protons collide at given x,y,z,t” or rather “two protons collide at given x,y,z,t in universe #554215”? How do you solve the apparent problem that the given definition of the event may not have sense in some universes, e.g. if the universe happens to be one-dimensional and have no protons in it for the example given above? If you simply mean “for any event, we can imagine a universe that contain it”, why did you start speaking about probabilities?)
Is this supposed to justify the previous claim, i.e. that the probability of any event in Omniverse is 1? If so, I don’t regard “each universe contains something, therefore any event has probability 1 in the Omniverse” a valid inference, whatever interpretation of both the premise and the conclusion I can imagine.
What is “long run”? Does it mean “in other universes” (that would make sense, but the choice of words “long run” to denote that seems bizarre) or does it mean “sometimes later in this universe” (that would be the natural interpretation of “long run”, but then the statement says “p(the event happens) = 0 and the event can happen”, which is a contradiction).
And of all that, how does anything imply, or even relate to, the “uncountably many” answer you gave at the beginning?
From the immediate parent:
This is an assertion without explanation. I even don’t understand what do you mean by “taking the universe as a QM event”.
From the single sentence the OP consists of, could you quote the section where it very clearly asks for non-standard instances of the (which?) question?
Good enough for me. The sensitivity is merely a measure of my newness to LW. But, again, the sensitivity wasn’t unwarranted granted your complete lack of explanation for the objection “I don’t follow”.
No, it doesn’t. The question posted by the OP implied the relevance of MWI of QM. Note, in order for QM to hold any relevance to us, it must be interpreted in some way. Yes, let’s proceed.
You obviously aren’t familiar with the concept (for which I cannot be held accountable). In any event, I’ll explain it briefly: the omniverse is that state of affairs in which all possibilities are realized. Hence, that any event should obtain therein is an absolute certainty.
No, not particularly. However, even if it were so, consider this: tell me of a universe in which nothing exists. Does it make sense to posit something of which there is nothing? Equivalently: There isn’t anything of the universe. But there is a thing, namely, the universe.
This is the standard understanding of what objective probability teaches: given any universe you please, a given probability of an event is supposed to hold for a particular situation in the case that one were to observe all cases (for all time). Thus, the “long run” considers a particular situation for all time. If you flip a coin, you will not observe an outcome of 50% heads and 50% tails, but were you to flip this coin for eternity, the net result is just such an outcome.
I’m not sure how you’d pose this question seriously. For one, the MWI and nature of QM decoherence shows a state of information as unrelated instances of a general state of things (in a coherent superposition). That there are uncountably many universes (as inhabited by any observer you please) in which the cat is alive, and so too for the cat being dead. The “cat” could even be an infinite variety of other objects, for all we damn well know.
Then you obviously aren’t familiar with MWI. Even Penrose and Hawking agree that QM applied to the universe implies MWI.
Are you being obtuse to justify your down-vote or something? This is ridiculous. Now I have to justify my answer to the OP to you? Absurd. But I’ll play along, quoting OP:
I think that the universe is a “non-50/50 scenario”, but I guess you can make the case it isn’t.
For your information, I am familiar with both concepts, I pose all my questions seriously and I don’t need to justify my downvotes. I also consider your debating style condescending and generally hostile. This prevents me from continuing in this debate.
Quite. I agree with argumzio and find the failure to consider other reasons for disagreement grating.
edited to clarify: his failure to consider other reasons.
His failure or my failure? If the latter: I find it difficult to understand argumzio’s arguments and as I have already said, I find discussion with him unpleasant. Perhaps you can restate his arguments in different words and show me what is his (and your) position. Then, if there is some disagreement, I will consider and address it.
The word ‘omniverse’ does not represent a recognized concept in mainstream physics. You give a definition for it and implicitly imply in your root comment that MWI implies the existence of an omniverse,
but provide no justification for this.
You are either using different definitions of “long run” or making contradictory statements across your comments. Here you state that this specific outcome will obtain in the long run, but in your root comment you argued that any alternative outcome can obtain in the long run:
You use the phrase “uncountably many” without providing justification. I can substitute this phrase with “countably infinitely many” and the structure and strength of your arguments would not be changed. Provide justification for why the cardinality of the natural numbers is not enough. (This was Prase’s point in eir reply to your root comment, which you did not address.)
This response is not constructive. Provide references. Also, you changed context from
to
without clarifying what you meant by the first phrase, which I cannot parse in a way that makes sense.
First, your tone unnecessarily escalates the hostility in this comment thread. Second, a binary quantum event in which the final quantum states have unequal probabilities is standard. It is the opposite, where the probabilities are equal, which requires specific preparations, because we would need to make sure that the square of the modulus of the probability amplitude of both states are equal.
If The Road to Reality (from which the term omniverse, or “omnium”, originally sprung) is not “mainstream”, then pray tell what is.
This is a technical aspect of the discussion, and is not contradictory. The point should be clear if one considers the possibility of flipping 100 heads in a row on a fair two-sided coin. For all intents and purposes, the probability is 0, but that it may happen is not in the least prevented or negated were we to consider an infinite (“long run”) flipping of coins. Pretty straightforward and not contradictory.
Had I devoted the energy to a full-length discussion of the topic, this probably wouldn’t be an issue, but (in general) it should be clear that the number of such worlds (or universes) should be uncountably infinite, not countably infinite. That is, the cardinality would be on the order of Aleph-1, at the very least. And I seriously doubt that had any bearing on prase’s original point.
I guess you could read on the topic, if you’re interested. I’ve already suggested at least two (namely, Hawking and Penrose). Do I really have to do all the work? I need to eat and making a living.
There is no “tone” here. That is a mind-projection fallacy. If anyone liberated of mammalian instinct can read what I say without imputing emotional overtones thereto, then it should be obvious that my points consist in reasoned discourse without torrents of bluster at all. It’s almost as if you people wish to say, “yeah, we can see you holding that 9mm, just waiting to bust a cap, and the foam dripping from your mouth”. It’s really rather cute.
Your last two sentences are interesting, but I’m currently short on time. Grant me that I will return to respond to them later. Thank you.
First, words and phrases become recognized in mainstream physics when they become widely used in publications, not when one well-known physicist uses them. There are 15 results on Google Scholar for a search of ‘omniverse’ within physics, and of those results, none has been cited more than three times.
Second, even within The Road to Reality—for which I have the first edition as an ebook—the word ‘omnium’ appears only six times in 1094 pages, where they appear within six consecutive pages (p. 784-9) in a single chapter (ch. 29). The index gives only one page reference (p. 783) for this word.
ETA: You disregarded my claim that “you implicitly imply in your root comment that MWI implies the existence of an omniverse [...] but provide no justification for this.” This was a main point.
I was taking what you wrote literally, because you remarked at least twice ([1], [2]) that you dislike the lack of technical sophistication in discussions here, from which I concluded that you must mean what you write when you use technical terms. Under this assumption of literal meaning, I contend that there is a contradiction in the two statements that you wrote.
I have nothing further to add to this line of discussion.
But this is the main point in contention! Recall that your answer to Smk’s question (“How many worlds?”) is
Prase and I pointed out that some of your subsequent reasoning and justification for this answer are unclear or incorrect. An argument for your answer is what I would like to see. You state that this is “clear”, but again, one of the main purposes of this comment thread is to establish whether your answer is correct or not!
I am reasonably well-read in Hawking’s and Penrose’s texts in popular science. (I assume you are not referring to their original contributions to physics because other physicists are better known for their contributions to MWI.) I still cannot parse your first phrase (“taking the universe as a QM event”). I think I understand what you mean by your second phrase (“QM applied to the universe”). Is the first phrase supposed to have to same meaning as the second phrase?
Then I must remind you that all commenters on Less Wrong are human, with the exception of Clippy. One of the purposes of this comment thread is to establish which claims are correct. If your arguments are correct, then you have nothing to lose by being more persuasive, and I claim that your tone was overly aggressive and not persuasive for most purposes.
I don’t need to justify what is common knowledge. Take note of Tegmark, if you and the other down-voters care to.
Wow, so you really think your strawman is sufficient as grounds for objection to what I’ve claimed as correct? I didn’t require sophistication of others here. That’s pure nonsense. But by all means, try to impute meaning into my posts where it wasn’t.
I have. It is quite clear. And the only objections I’ve seen consist in mere definitional confusions on the part of the “objectors” or who don’t seem to demonstrate an understanding of the claims I made, but instead contend that I’m merely being “hostile” and not persuasive enough.
Not necessarily the same “meaning” but more or less the same pragmatic thrust.
You make an interesting, and fallacious, claim, and continue to hide behind smoke and mirrors by suggesting that I haven’t answered your so-called objections.
Going back to your last post:
What exactly is “it”? I’m referring to the universe, not the cat’s being dead or alive. What exactly is the relevance of the probabilities being equal, in any case? Does that even impinge on anything I’ve said, or even anything anyone else has said? Not obviously so.
I am responding to Argumzio’s comment in several separate replies. This is my first reply.
I assume that you are referring to Tegmark’s ideas on his multiverse hierarchy and his ultimate ensemble. If I am incorrect, correct me, and point out which of Tegmark’s ideas you are trying to use. Tegmark’s speculative ideas are certainly common knowledge within the physics community. They also fail to justify your claim that MWI implies an omniverse.
Your definition of the omniverse and your subsequent uses of this concept does not clearly indicate whether you mean a Level III multiverse or a Level IV multiverse in Tegmark’s terminology, so I will provide rebuttals to both cases. I shall be referring to Tegmark’s most recent elaborations of his multiverse hierarchy in arXiv:0905.1283v1 (2009).
Suppose that you wish to claim that your omniverse is equivalent to a Level III multiverse. Then you have trouble because Tegmark counts at most a countably infinite number of worlds. In particular, Tegmark states that
Tegmark’s calculations for this are in Footnote 5 on p. 4. The obvious extension of this calculation (by scaling the temperature) shows that there is a finite number of universes below any temperature. This implies a countable number of universes even if we grant an unbounded temperature, because we can easily get a bijection with a subset of mathbb{N} by enumerating the universes below any arbitrary temperature.
So this does not work.
Suppose that you wish to claim that your omniverse is equivalent to a Level IV multiverse. Then I fail to see where Tegmark claims that MWI implies an omniverse. On the contrary, Tegmark is careful to distinguish between a Level III multiverse (MWI) and a Level IV multiverse.
Furthermore, it is not clear to me how Tegmark’s Level IV multiverse can be equivalent to your omniverse. Tegmark defines the Level IV multiverse as one in which
This is not equivalent to your definition of the omniverse, where
Tegmark makes no mention of events occurring within the Level IV multiverse, while the context within which you defined the omniverse mentions only “events”, not mathematical structures. Nota bene that Tegmark does mention quantum events occurring, but only in the Level III multiverse, which I have already concluded is different from your omniverse.
I no longer believe that you are throwing names of well-known physicists in good faith. Thrice you have done this:
Not once have you provided any reference to go with the names. Of the single reference that you gave in this thread, to The Road to Reality, it was erroneous justification for the word ‘omniverse’ being recognized in mainstream physics.
I welcome any refusal to give arguments that have already been given elsewhere. But if you are going to name names, then provide references. I should not have to say “I assume that you are referring to Tegmark’s ideas on [...]”; I should instead be able to say “I agree with section A in Tegmark (2009), but...”
For what it’s worth, I never downvote replies to my comments; I recognize that this disincentivizes replies. However, I have indeed downvoted your root comment and your replies to Prase.
Well, I certainly consider this my last reply, because 1) I grow weary of this straightforward enough topic, 2) respondents have hitherto been enthralled in a childish, eristically motivated game of serving a slapdash of trivial, illogical, and baseless complaints one after another, 3) my posts have been consistently down-voted, which I find highly annoying, and 4) my grasp of the subject – and general familiarity with (and understanding of) the connections between the concepts omniverse (from omnium=multiverse), MW, QM, probability states, and the infinitary conclusion that is obtained by noting the (well-established) opinion that we live in an inflationary universe (that may well be eternally inflationary) – has no need of a “well-reasoned” or even “pursuasive” (an interesting way to move the goal posts, I might add) justification, insofar as there is a body of literature out there that suggests the pertinence and correctness of the answer I provided (which I never said was the true, in-your-face-clear-as-day answer).
(FYI: another source, of which I was previously unaware, that raises some of the key points I have is Brian Greene’s The Hidden Reality, p. 181 onward. It does so in a largely jargon-free, not-so-overly-technical manner, so I suppose that should be a relief to LWers.)
Very well. Thank you for letting me write the last word. I shall in time respond briefly to your previous comment—as promised—and also provide a summary of the outstanding issues that you never addressed. Although they will be directed to you, I do not expect any response from you, and I will not consider it a breach of LW etiquette for you to ignore them.
A reasonable sentiment.
Then show these childish and eristic respondents what a mature and sensible argument looks like.
Destroy those trivial, illogical, and baseless complaints with useful, logical, and grounded responses.
If you wish, I am willing to create new accounts and mass upvote your comments if that lessens your annoyance and allows you to continue in this thread.
I am delighted to know that you are an expert.
Oh, certainly. Your grasp of the subject is indeed disconnected from well-reasoned justification.
… I apologize; I was being sarcastic and that was an unfavorable literal reading of what you wrote. You probably meant something like “I don’t need to present ‘well-reasoned’ or even ‘persuasive’ justification here.” In which case I am flabbergasted. Why are you writing here if you are not trying to give well-reasoned arguments? I can understand this if you provide lots of references to well-reasoned arguments that others gave, but you did not; you gave lots of names. Furthermore, you claim technical dominance ([1], [2], [3], [4]), and yet you have not named a single technical paper or survey of the subject; the two references that you gave were both popular science books for a general audience.
I never moved the goalposts. Out of the 729 words in my first reply to you, only 10 words were about your lack of tact (“your tone unnecessarily escalates the hostility in this comment thread”). You then devoted a paragraph to justify your aggressiveness by appealing to non-mammalian readers. In my subsequent reply, I spent only one paragraph out of nine to respond to that, and thenceforth never mentioned it again. Moreover, I never insinuated that your aggression is relevant to the topic at hand—I commented on it because it was relevant to the atmosphere of the discussion, which you were making unnecessarily antagonistic.
You keep running into the goalposts and claim that I moved them.
See my comments (both in this reply and in previous replies) about your reticence to provide references.
To conclude, I apologize for the intellectual gulf between you and me, and I wish you the best of luck in other academic disciplines.
I apply the same policy.
Don’t sweat it. I don’t think much of this nonsense “karma” thing. It’s a total joke but makes sense only for those who regard the “wisdom” of the mass as somehow reflective of a post’s quality. A post should be judged according to its merits, not the “points” accorded to it by (anonymous) persons who can’t provide a justification for their vote.
In fact there are many continuous outcomes in quantum mechanics. The overved velocity or momentum of an electron or any other mass. In fact the number of stated problems where the results are broken down in to discrete states is small compared to the ones with continua. In fact, the heisenberg cat example, there are not just two states of outcome, either alive or dead. Rather there are a myriad of state outcomes where the cat is alive, and another myriad of outcomes where the cat is dead.
I personally think the many worlds hypothesis is ludicrous, failing Occams Razor by such an astonishing margin that it might as well just grow a long beard. Admittedly, I have not read any respected physicists argument for it (or at least I didn’t respect the arguments I did already read). I think the many worlds hypothesis is just a very dopey hack for people who have decided ahead of time that the universe “just HAS to be” deterministic. I say if you observe indeterminism in the universe, then it is your theory that is broken, not the universe.
You don’t agree that Decoherence is Simple? (Not that I’m qualified to have any opinion on the matter.)
I’m glad you gave me that link, thanks. I had seen that article a while ago and it was good to refresh.
The problem with the Many Worlds Hypothesis is that it solves no problem, in my opinion.
In simplest terms, the problem with the “standard” interpretation is that you have probabilistic outcomes from some experiments. Some people hate that.
The “solution” offered by MWI is that at every instance where a wave function would have collapsed to some probabilistically determined valuewe have the universe split into as mny choices as there are possible wave function collapses, even when that number is infinity because the wave function collapses into a continuum of position or velocity values. And this happens over and over and over so you have an efflorescense of zillions and 3^^^^^^3 and googleplexes of universes.
What problem did this solve? Oh yeah, the arbitrariness of the probabilistic result predicted in quantum mechanics.
What problem did it not solve? That I wound up in this particular universe, no physics to explain that. “Oh, but you wound up in ALL the universes!” I got cloned a zillionplex times with the universe. So did everybody else. In fact you got cloned a zillionplex times when a wave function collapsed because I observed something, and then your zillionplex clones got cloned another zillionplex times when you observed something, and then a zillionplex more splittings of each of you for each wavefunction collapse for each of the billions of humans on the planet. Do ants have enough “observer status” to collapse wave functions? Probably, if not ants than certainly frogs.
So we wind up with a near meaningless explosion of universes that is constantly going on, and indeed is in important senses accelerating constantly.
And of course every one of these overwhelmingly zillionplexes of zillionplexes of universes is unobservable to us, will never have the slightest affect on us, once they split off from us!
Its almost as though they don’t exist!
Except things like quantum computers. It’s almost like those worlds do exist and that we can even use their transistors to parallel process stuff.
Well that is definitely a fun thing to say. It doesn’t seem to be consistent with what is currently thought about quantum computers and Many Worlds, though.
Your link to the wikipedia article on the MWI does not clarify your objection to the statement made above.
The wikipedia article states
If a quantum computer could correctly be characterized as a computer which utilized the transistors in other branches of the multiverse to speed up calculations in this one, then it would merely require the operation of any quantum computer at all to provide strong evidence for the multiverse. However, the article states that a test for MWI requires a particular special operation of a particular special quantum computer, that the multiverse is not a conclusion we reach merely by seeing a quantum computer work.
Sorry I didn’t make that connection clearer before.
I’m pretty confident that that paper is in error. Or rather, it assumes that the Copenhagen Interpretation is implemented so that it deviates from pure Quantum Mechanics in a particular, testable, way (or category of ways) - and that renders his version of CI distinguishable from MWI, and less useful for quantum computing. When I get academic library access again, I’ll take a closer look at it.
Upon returning and rereading… no. Branches in MWI aren’t said to have ‘split off’ until they are mutually decoherent. That renders them unsuitable for quantum computing.
The chief virtue of decoherence and MWI (as I understand it) is that it avoids ‘the measurement problem’ or the necessity of a natural observer. If you go back far enough in the history of the universe, there were no natural observers.
Well the beauty of the actual system is that you don’t need a “natural observer” until you have one. You calculate the time-evolution of the system with non-collapsing wave functions, then you collapse the wave function only when an observer finally shows up to make the observation.
It doesn’t matter if the wave functions were waiting billions of years to finally be collapsed, you are not missing anything by not having collapses before you have natural observers.
meaning the standard QM interpretation?
But consider the first natural observer, composed of matter. At what point do the wave functions associated with that matter collapse? Before or after its first observation?
With decoherence & MWI, this question presents no problem.
Irrespective of my below comment where i get more empathetic wiht the motivation for MWI, I do want to point out some of the reasons why I think MWI may be a “bridge too far” to solve any problems.
The universe as we know it has proven to be gigantically “conservative” in the sense of having a bunch of conservation laws that it simply never violates. Conservation of mass-energy being among the deepest and most powerful. In this universe, at this epoch, stuff is neither created nor destroyed: it is converted from one kind of stuff into another with strict conservation. Even particle pairs that arise from random vacuum fluctuations all soon “realize” if they are violating conservation of energy and disappear before you can say within the uncertainty principle that they were ever there.
So now we come along, have a subtle issue with wavefunction collapse and what really causes it and what does it all mean, and the solution is: the universe may be strictly conservative, but the multiverse is growing in total mass and energy about as fast as any growth fuction that you can conceive, and THAT is what makes the direction of time so strong?
Yes, of course this COULD wind up being right and being the simplest. I await proposed experimental verifications, without them I can NEVER pick a non-conservative multiverse.
But thanks for making it clearer what some of the things that are gained are.
That’s not how MWI works. These worlds are not being created. The wavefunction of the universe is being split up between them.
Are there more of these worlds now than there were 15 billion years ago?
If so, you can call it anything you want, but I vote that “created” is a pretty good term for explaining something that exists now that didn’t used to.
I failed to mention one major additional point. Decoherence and MWI also account for the observed fine-tuning of the universe to support life, including key details of the inflation hypothesis. The standard interpretation doesn’t.
As to conservation of mass-energy, this seems to be something that conflicts with your intuition that if there were decoherence, mass-energy would be divided up into the various branches and thus diminished in each branch. If you did accept the superiority of decoherence & MWI over the standard interpretation, you’d have to set this intuition aside.
You are free to select the version of Occam’s Razor that appeals to you. I like the one that chooses a complete explanation (that also explains fine-tuning) over an incomplete explanation that also requires an exogenous wave-collapse for the first natural observer.
Yes I see the motivation there. MWI may seem like an OK alternative to wave functions actually changing in the presence of consciousnesses, but not in their absence.
I guess I’ve never really believed the consciousness was an important part of it. Take for example setting up a two-slit experiment with a slow stream of electrons launched at it and a recording electron detector array beyond the slits. One would have a time series of locations the electrons hit the array which would probabilistically over time build a two-slit diffraction pattern, but in which each electron particle was identified with where on the array it ended up. Suppose you set this up in a room. In one version you send an observer in 3 days later to look at what happened, and you see all those evidences of each electron wavefunction collapse into a position eigenstate on the array detector. In the other version you don’t send someone in to the room until 10 years later, at that point the observer sees the historical record of all those wave function collapses. Finally there is a version where you never send someone in to the room.
It has always been my opinion that whatever collapses happened actually happened at the time recorded for each electron wave function hitting the screen. The version of the Copenhagen interpretation used here seems to go with the idea that the entire room including the detector array and the equipment used to record its results exist in a quantum superposition of all the wavefunctions UNTIL the observer finally goes in to the room, at which point they collapse in to a state with all the data stored showing one allowed version of the historical record of electron collapses.
Very intriguing. There is literally no way in this experiment to distinguish between “the wave functions collapsed as the electron hit the detector, that I came along later to see the record of it isn’t what caused the collapse” and “all possible histories of that room were swirling around in a quantum superposition until I finally came along and my peaking in the door caused it to collapse on to one possible outcome.”
I’ve never fully understood Bell’s theorem and EPR, but I suppose I am stating a version of the same question. How do I design an experiment that distinguishes between that room being in a quantum superposition until I finally get there, and that room being a dry tomb of the records of wave functions that collapsed long ago? Bells theorem, if I am right and it applies here, says you can distinguish and that the room does exist in a quantum superposition until you get there, that there are certain subtle statistics of correlations that are true but not possible in a room which is merely the tomb of old dead wave functions.
I realize as I participate in this discussion that for me, the collapse has been a result of the wave function and the observing EQUIPMENT, not a function of my consciousness. It is possible that Bells theorem test results mean I am just wrong about this, but maybe not and bear with me.
I did work for years on the quantum treatment of one example of “measuring equipment,” a linear amplifier for radio waves. The quantum uncertainty in radio waves is manfested as “photon counting noise.” You think you have a pure sine wave, but it has some randomnesses due to quantum uncertainty, and a variety of bookkeeping methods for characterizing that uncertainty show it is equivalent to one-photon’s worth of noise power in the system even at absolute zero of temperature when all removable noise has been removed. THe linear amplifier, we see, amplifies those fluctuations so at the output of the amplifer those quantum fluctuations are now large, comprised of the energy of a million photons each (for an amplifier with gain one-million) and therefore, essentially, treatable as a classical phenomenon. My interpretation is: the linear amplifier collapsed the original input wavefunction, and turned its quantum noise into solidly instantiated classical noise.
But I have a feeling if I understood EPR and Bells theorem that I would see it is not the amplification that collapses it. Hmmm.
This is the hypothesis that was tested, and failed, in the 2007 implementation of Wheeler’s delayed choice experiment.
Thanks for the link to Wheeler’s experiment. This experiment doesn’t address what I was addressing.
In wheeler’s experiment, the detector is put in place or taken away after the photons would have had to have passed through the slits. Even though the choice of detector (difraction pattern vs which slit) is made after the photons pass through, the photons are not “fooled” by this and behave at whichever detector is there when they get to it exactly as they should according to QM.
In my experiment, the detector and a recording device are locked in a room with no observer. The detector is never changed, the experiment just takes place without a human observer. It isn’t till sometime later that th room is opened and some human comes in to see the results of the experiment. The human does indeed see a time series of recorded electron hits on the detector which when summed up show the famous diffraction pattern. The question I address is:
Did the wavefunction for the whole room including the detection apparatus not collapse on to one of its allowed outcomes until the human finally went in to the room to see the result or
Did each electronic wavefunction collapse at the time the computer records the detector saw that electron?
My intuition has always been that it is not so much a consciousness seeing the result of the experiment that causes the collapse, as it is something about the apparatus for detecting the outcome of the experiment that causes the collapse. That the wavefunction is spread out across the detector array and then BAM it all gets sucked down somehow to only a single element of the detector array which is triggered.
In this view, wavefunction collapse is much more mechanical than in the way Copenhagen gets talked of around here.
Also, I think that whether the WF collapses when you go in the door, or whether pieces of it collapse each time an electron is recorded at the array are possibly experimentally indistinguishable. However, it may be that Bell’s Theorem EPR experiments do speak to this situation, that there would be experiments in closed rooms that could be done where an earlier collapse vs a later collapse when the observer finally arrives could be distinguished from some subtlety in how results are distributed (which is how I see EPR).
You have my condolences. I have waged this battle here for some time, without much success. If you press EY on the matter, all he says is something along the lines of “MWI is decoherence, decoherence is MWI”, which renders the MWI a redundant concept. Unfortunately, nearly all non-experts here fall into the password-guessing trap, while furiously denying it. Probably because the MWI seems so cute and even intuitive, even if bereft of substance.
Indeed. Thank you for making the points you did in the first paragraph; that’s more or less what I was making note of (in perhaps too-general terms). I was going to respond to another post that falsely contended that just because there are two states that that necessarily exhausts all of the possibilities that obtain (as ens rationis), since the state of the cat as such is not discrete, but also continuous.
I would not be so quick to dismiss MW on account of the heuristic value of the idea of multiverses (and the successive hierarchy of universes), because rationality cannot be used to dismiss the preeminent possibility of any possibility. Anyway, there’s a pretty interesting article on arXiv by R. Vaas about it: http://arxiv.org/abs/1001.0726 .