November 23, 2008

Open forum: dish against or defend many-worlds and decoherence theories

Over time I've left many remarks (and many very recently) critical of many-worlds and decoherence theories at blogs such as Uncertain Principles, Quantum Pontiff, etc. I can be at bit of an irritant so I don't want to wear out the OPs that I criticize, many of whom indeed don't have time to follow up on my depredations. Here's a forum to discuss the problems of such theories, especially if you were debating with me at another blog. Do also check the previous post about "quantum stupefaction" which is sort of silly, yet may have actual implications for MW concepts and related.


Anonymous John G said...

What's the problem with there being bosonic connections between the many worlds during the superposition and none of these bosonic connections after the superposition. There are gravity explanations such as GRW and Orch-OR and resulting environmental effects that can say why the bosonic connections go away. There's certainly no consensus on how gravity and quantum mechanics meet but that doesn't mean that they don't meet in some way.

23/11/08 13:59  
Blogger Neil' said...

John, I am OK with ideas about how to actually cause objective collapse, such as GRW and Penrose/Hameroff etc. However I haven't heard any connection to "bosonic" issues. Yes photons are bosons and that makes for odd statistics that feature in quantum mysteries. However, a fermion like an electron is also spread over a region of space until "collapsed" and that needs explaining too.

I just don't like decoherence because meddling in interference only disrupts the orderly relations between waves that are still widely dispersed, it doesn't say way the condense into a localization to make a "particle." And any notion that when I see an event at detector-1 there is also a finding of the same entire particle (!?) at detector-2 etc, is an absurd violation of conservation laws etc. - it is another universe just pulled out of someone's, er, stoned imagination.

23/11/08 20:36  
Anonymous John G said...

The fermion isn't spread, there's just lots of paths with the fermion on them. The bosonic connections are whatever connects these paths while there is a superposition. It would be some vacuum connection via something like longitudinal photons or vector gravitons. The other universes are there in their entirety with conservation laws just like ours. From the point of view of the other universes it would be our universe that would seem to be pulled out of nowhere cause the longitudinal photon/vector graviton (or whatever the vacuum connection is) bosonic connections do come and go between the universes via the superposition coming and going.

24/11/08 00:07  
Blogger Neil' said...

John, please explain "longitudinal" photons and vector gravitons (as distinct from ordinary photons and gravitons, or an unorthodox take on the same familiar particles instead?) BTW note that "paths" don't really justify a complete particle at each place - again, paths, components etc. of WFs represent partial amplitudes of full presence.

24/11/08 20:10  
Blogger Neil' said...

Here's a relevant comment of mine, reposted from CV thread:

If you believe that the wave function is real, then nature is not really time-reversible after all. Consider that at an “emission” point the WF expands out and gets bigger and bigger, but then (maybe) “collapses” at the absorption point. Run that backwards in time and it will not go the same way. Well, some people say something like many-worlds takes care of that. I suppose if the wave keeps evolving then there’s no time-asymmetry problem? However, with unobservable worlds/branches, it looks “not even wrong” from here. Also, modified from a point I made at Uncertain Principles, here’s an issue relating to expansion of the WF and the issue of time:

Regardless of whether you call it a literal “other world”, I in this one observe a specific outcome. If you think the other outcome/s must be actualized then it has to be “somewhere” in some sense of the term. (It’s gross because we are making more of the total integral of the WF over all spaces/?s combined, to have the whole particle “here” as well as the whole particle “there” - but let that go for a minute.) We still have to justify “my” chance of getting various chances of the outcomes, even granting the bastardization of conventional statistics (one person confronting multiple cases in sequence) into the idea of how likely a random “version of you” will run into a given outcome in multiplications of a given trial. Well, suppose there are two possible outcomes, but the chance is not 50/50. I ask: OK, so how many worlds/?s are created in the split?

The temptation above is to say “two” since there are two things that could happen. But suppose the amplitudes reaching detectors are 0.8 and 0.6. Then the probabilities are 64% and 36%. So now what, we have 64 “worlds” one way and 36 “worlds” the other way, or 16 and 9, or …. to get the right proportion of chance for observation? What number of versions is appropriate? What if it’s an irrational proportion? If you have infinite branchings, then how can you define “proportion” given such infinite sets? And even if you say, it really isn’t a matter of n specific separate worlds, how then does the proportion manifest if you somehow put “all” the particle into both detectors to avoid collapse into only one of them?

No, it seems that the WF must actually behave inherently differently during absorption/detection than emission/creation, which is asymmetry in time. I think our problem with “collapse” goes beyond just the “metaphysical” issue of what happens during collapse, but even what sort of “interaction” should cause it to happen. If we leave humans out of it, some might say “detectors” are inherently special, maybe from decoherence. But consider a photon entering a Mach-Zehnder interferometer. Why doesn’t the first beam splitter “collapse” the photon so we don’t even get interference from recombining? That silvered surface has atoms which are excited by the photon for “re-emission”. (Or indeed, why not consider the “split” photon to be one in each world for each possible direction, already?) But if a phototube gets a click, many assume that really happens (unless “awareness” makes it so.)

Hence I don’t think we can avoid the odd challenge to “time” in physics presented by wave function issues. Wave functions tend to get bigger as time progresses - is that perhaps even more fundamental than thermodynamic issues?

24/11/08 20:13  
Anonymous John G said...

Well perhaps an orthodox view might be if you use the string theory concept of our world living on a brane, then the longitudinal photon or vector graviton could be called a virtual graviton or virtual photon and it would be a closed string whose ends connect to two different brane-worlds.

For David Deutsch, each of the many worlds are very real so the electrons seen in other worlds are seen just as we see our electrons. Other people do see the many worlds as being virtual ones during the superposition which to me isn't any better than the Copenhagen interpretation cause everything virtual, nothing real during the superposition isn't any better than not being able say anything about it.

25/11/08 14:35  
Blogger Neil' said...

OK John, hopeful musings but what about the problem of unequal probabilities at the split, as I said above?

26/11/08 11:20  
Anonymous John G said...

Since I'm now talking string theory, I can kind of cheat and just handle probabilities the way string theory does. You integrate over the worldsheet paths between your starting point and all the possible ending points. That basically means you have more strings going to braneworlds with the higher probability outcomes.

I should make one additional comment that these many-worlds brane-worlds are reached by strings that go through a complex bounded domain (the worldsheet). People also talk of brane-worlds that are physically nearby ours with strings between them. In this case the strings go through a real domain (spacetime) and you have actual gravitational attraction between the brane-worlds.

26/11/08 12:04  
Blogger Neil' said...

OK, but REM that the multiplicity of dimensions and worlds in string/brane theory is not the same as MW splitting in QM. One can accept the former and not the latter. No one really understands the physical "basis" of MWs, but strings and their effects can be imagined as fundamentals. If you ever work out a way to deeply relate the two, your brilliance will be hailed.

26/11/08 13:00  
Blogger Neil' said...

Here's another important issue about interference versus "classical" behavior etc:

We can cheat interference and "one way" issues by e.g. putting a half-wave plate just before or even just beyond one of the double slits (S2.) If we illuminate with say "x" linear pol, then x gets thru S1 as is but x pol. is turned into "y" pol. at S2. They are orthogonal, they "don't interfere" (per intensity!)

However, if I measure with little polarizing meters I can find an alternating pattern in the diagonal angle of polarization on the screen: the direction of diagonal polarization flips back and forth across the screen in the same way net intensity would do in a traditional interference pattern. The changing phase relationships of the x and y pol. from the slits do that! So it seems I could have "one way" info about which slit (if I measured x versus y instead of diagonal), but really I can still find the interference pattern by making the right kind of observation. (Someone already did this sort of experiment.) Hence mere interference or lack of doesn't localize photons.

27/11/08 22:07  
Anonymous John G said...

"Hence mere interference or lack of doesn't localize photons."

I'd agree with that. The "which way" information has to get entangled with our Orch-OR decoherence cycle to ruin the superposition. Without us Orch-OR beings, there can still be entanglement with GRW decoherence cycles.

28/11/08 19:17  
Blogger Neil' said...

This comment has been removed by the author.

10/12/08 21:20  
Blogger Neil' said...

Wow! I have sort of been immortalized from a prominent science blogger dedicating a post to me! I am one of those who endlessly argue about "the collapse of the wave function" but I add that it is not resolved by decoherence concepts. One of the targets of my nuisancing is long-suffering Chad Orzel at Uncertain Principles. Today he "honored" (;-) me by setting up a thread in my name: Official Neil B Quantum Measurement Thread

I made my first comment wearing pajamas in my mother's house, for real. Check it out! It's not all just "philosophy," I included an experiment with changing polarization at one of two slits that seems to have real implications.

10/12/08 21:25  
Anonymous Allen said...

I saw your comment on Modal Realism and the platonic mindscape over on Cosmic Variance. Where did you come across all that? You are not a modal realist, correct?

8/1/09 14:48  
Blogger Neil' said...

Allen, I heard of modal realist ideas off and on for years. I think I first browsed a good exposition and defense in Frank Tipler's The Physics of Immortality (1994: ISBN 0-385-46798-2). I hadn't yet heard of David Lewis, the stated "founder" (made a definitive exposition, as with lots of ideas that float around and are attributed to various "polishers") of modal realism. Such ideas have been actually around for quite awhile before Lewis. Tipler's argument was flabbergasting to my sensibilities. Yet I had to admit, I couldn't find any (NB) purely logical way to refute the idea that conceptual Platonic constructs were not "real" in a way that "stuff" was - by distinction - actually real in some superior way. And if you think about it, and as David Lewis more formally argued (see, there really isn't. Logic just has no way to describe substantive existence and specify just what makes it special and true, versus statements about mathematical entities like perfect ellipses (ratios of radii to circumferences, etc., roots of equations.) I also saw the idea vetted by Paul Davies in the wonderful The Mind of God, although Davies doesn't accept it either, and Penrose has explored the idea and also rejected it. Max Tegmark says he believes it (all mathematical structures exist, the world is "made of math" etc. - gee, what about what things feel like, Max?!) Of course, it is a hilarious irony then, that “materialism” – the stuffy essence of rational fortitude for centuries – is revealed to be a metaphysical conceit, something that can’t even be coherently stated!

Everything you think would do the trick to make the distinction work is really a circular argument or leans on some hidden assumption or intuitive/experiential "getting it" factor, believe me. But to me, that's just the point. Logic isn't all we have, and our conscious experience is a definitive and vivid "something" that can't honestly be evades. Instead of thinking experience is needed to collapse specific wave functions, I say it is a marker of "realness" in general. (BTW I think we still don't understand that anyway, especially since the decoherence proposal has feet of clay. I put down the latter by calling it “decollusion.”) Not that we need to look at the Moon to make it exist (there’s that metaphysical word again!), but whatever generates the experiences we do have when looking at the Moon is only real in a universe where experience can be real also. Note I say, can be, even if not yet expressed. Hence no need to worry about keeping the world in existence before humans or multicellular animals or any life or whatnot.

Neither do I believe that all possible worlds (universes) exist. They all must exist in Modal Realism because it holds, there is literally no such thing as a distinction between a PW that "exists" and one that is just "an idea" or such. But if we don't believe in MR, then it becomes a problem to explain just why some PWs exist, and others don't! The glib attitude many scientific writers have (like Sean in Cosmic Variance) that a particular kind of world can “just be what exists” is inexcusable. As I like to say, that would be like the number 23 being made up in brass numerals while all the other numbers have to remain mere abstractions. There is no logical way for such a special property that transcends that very state of abstraction, to be conferred without some contrivance. But I have written elsewhere about what goes wrong if "all possible worlds exist" as an alternative to such selection (for one thing, Bayesian expectation arises of a chaotic future.) My answer is, “Goddidit.” Sure that’s not science, it’s philosophy, but that’s the kind of question it is to start with. (Because I base it on thought process and not traditional revelation etc., it really isn’t “religion” either.)

8/1/09 20:32  
Anonymous Allen said...

Ahhh! Yeah, I'd heard of modal realism, quantum MWI, Tegmark's MUH, platonic realism, subjective idealism, etc. and have spent a reasonable amount of time thinking about it myself.

Though, I've come to the opposite conclusion as you. Which is that something like modal/platonic realism must be correct. I don't see any other explanation that makes more sense. Kind of the Sherlock Holmes thing: Once you eliminate the impossible, what remains must be true, however improbable.

So from what I've read of your various mention posts around, I think we're pretty much in agreement as to what the problem is, but we've taken approximately the same facts and arrived at different conclusions.

Introducing God seems like it just explains the mystery of consciousness by introducing the mystery of God. And of course God raises a whole nother host of questions. So you've answered one question by introducing even more questions...or so it seems to me.

So I have an engineering background and took all the usual college science and math stuff. I'd been an atheist since high school, and lost my faith in free will in a class on quantum mechanics.

But, probably my first introduction to this even stranger stuff was Hans Moravec (

Also, believe it or not, Greg Egan's short story "Wang's Carpet", and his book "Permutation City" where he talks about "Dust Theory" ( were also helpful in realizing that there are some strange things afoot with consciousness and reality.

But I didn't fully understand the real weakness of materialism/physicalism until I read David Chalmers' "Facing Up to the Problem of Consciousness" ( Reading that was an epiphany, sort of a bolt from the blue. I suddenly saw the problem that had been right there in front of me all along.

I don't agree with Chalmers entirely. In fact, I only half agree with him. But I think he's on the right track when he says: "Physics is information from the outside; experience is information from the inside." (

He calls this the "double-aspect theory of information", which posits that consciousness is just a fundamental feature of certain types of information. Maybe all types of information have some degree of consciousness, but certainly information such as that represented by a human brain at any given instant in time is conscious.

So I think that it makes more sense to accept this one thing on faith, and then everything else follows from it logically, and there really are no other open questions. More sense than believe in an actual external reality which introduces a lot of probably unanswerable questions (where did the universe come from, what is energy, what do we have the physical laws we have, why something rather than nothing, etc), or God who introduces at least as many if not more.

Occam's razor points to some variant of modal or platonic realism I think.

But, I'm very interested to hear anything else you have to say on it.

9/1/09 01:33  
Anonymous Allen said...

My basic point being that any theory of reality has to have something fundamental at the foundation that is taken as a given.

With materialism, the foundation is energy, or maybe spacetime, or quantum fields, or some combination of all three. But unless you just accept the existance of these things as fundamental brute facts, the next question is obviously "What is energy?", or "Where did spacetime come from?"

With a religious view, you say that some supreme being or supernatural force is at the foundation of your reality. But this introduces the question of "What is God?" or "Where did God come from?" or "What is God's motivation?" or "What does God want"?

In my view, the best candidate for the fundamental core of reality is: information. With the extra assumption (which is well grounded I think) that certain types of information have conscious first person subjective experience. The idea that information exists independently of any physical substrate, as in Modal or Platonic Realism is I think not to big a stretch. And once you take this as your theory of reality, there really are no other questions. Everything else follows.

This does lead one to conclude that most conscious observers see a completely chaotic and nonsensical realities. BUT, so be it. We have examples of such conscious observers right here in every day life. People with schizophrenia, dementia, hallucinations, etc. All of these conditions are caused by disruptions in the information represented by the brain. Which is why I think even assuming physicalism, you're still lead back to idealism.

And of course, you have experience of nonsensical realities yourself, when you dream. I would say the worlds we encounter in our dreams are just as real as the world we see when we are awake, BUT we don't spend much time there, and when we wake our memories of the dream worlds fade and lose intensity. So we give them subordinate status.

So, to summarize, I would say that every possible conscious observer exists in a reality of their own perceptions. And every perceivable reality (both hellish and heavenly) IS perceived by every observer capable of perceiving it.

9/1/09 13:06  
Blogger Plato said...

Interesting thoughts Neil.:)

2/6/09 10:25  
Blogger D said...

Hi, Neil'!

I saw you mention modal realism over on He Lives, and that seems to be drying up in terms of productive discussion. Here's the limit of my physical understanding of the situation, including where I still have questions.

Things get really complicated from there, I'm not even sure where to begin. I can say that I know I don't have all the answers, but I'm pretty sure that modal realism is possible, I don't buy it, and I don't really see any unambiguous evidence for it. It certainly plays havoc with my understanding of the words "possible" and "world," though...

5/10/09 00:58  
Blogger Neil' said...


Thanks for coming by. Modal realism: I don't believe it's true, I use it as a "foil" to make other points. What do you think of the paradoxes of quantum mechanics?

BTW, there's still an interesting discussion at He Lives, and I made some thoughtful, long remarks. The discussion is civil enough now, you might consider dropping in again. BTW', from your blog handle/pic I figure, "female" despite not challenging re "male" assumption about you (many presume; many don't bother to challenge.) As you wish.

5/10/09 16:02  
Blogger Neil' said...

BTW'', I left a comment at your THINK forum:

5/10/09 16:06  
Blogger D said...

Hello again, Neil'!

OK, so whenever I start talking about modal realism, I just get headaches. I had a discussion on LiveJournal with some friends a long time ago, you can read it all right here.

But that's really long. What it comes down to at the end of the day is that modal realism is unfalsifiable. There is no test that could even potentially prove it false, which means that we can't prove that it's true (if you can't know you're wrong, then you can't know you're right, either).

Of course, that's only what I think so far, given the evidence available to me. When new evidence rears its head, I'll have to investigate and change my mind. Keeping up on science is hard work!

And speaking of science, the paradoxes of quantum mechanics tell me one thing above all others: reality is complicated, and the idea that it is (or ought to be) easily comprehensible to us is vanity. As for particular bits, if you had this or that paradox in mind, I'd be happy to expound if you point me at it.

So yeah, that's what I think of that stuff in a nutshell. Have a great one!

10/10/09 16:09  
Blogger Neil' said...

Thanks for dropping back in, D. I'll have to join LiveJournal to see that discussion - I'll try to REM that. Modal Realism: well, I'm not sure it's unfalsifiable. There are ways to challenge the idea of an infinity of logical worlds and there being no special, distinct form of "genuine existence." One way is possibly special features like conscious experience, "real flowing time" (look up "block universe" and theories that "time is an illusion"), and genuine randomness - as supposed for quantum mechanics.

Of the latter, think: mathematics is a deterministic system because of logical entailment. A "mathematical structure" cannot produce random digits. (I don't mean, a unique set that looks random. The digits of pi or square root of two are not "random", they are "necessary" according to what makes up that number. But take two identical muons, and one decays at a different time than the other.) Quantum randomness is supposed to be "genuinely random", with the whole idea that "identical states" don't all do the same thing, but sometimes turn out one way, sometimes the other - with no predictability. That violates logical necessity.

Also, if all PWs existed, then we'd have Bayesian expectation problems: we'd be most likely to be in a world just orderly enough (and even then, only up to that moment) to permit our existence. Why? Because there are so many more ways for the latter to exist, than our own. (Like, more ways to make a sloppy collection that the symmetrical ones.)

Well, that leads right into QM: IMHO you are so right about QM, and I especially like and agree with this:
"reality is complicated, and the idea that it is (or ought to be) easily comprehensible to us is vanity." So many people think that reality should be easily comprehensible. Try googling "quantum measurement paradox" and see me in the first 10-20 hits, with a version of a measurement paradox. I will try to post a version of my best paradox soon.

PS: I put up a post about First Causes etc. at that philosophy blog you namelinked to. And BTW, aren't you impressed that at a believer's blog like David's "He Lives", you can get that kind of intellectual quality in both posts and comments?

10/10/09 21:10  
Blogger D said...

Sorry, I didn't realize that my friend made his journal entries all private. My mistake there, I'll nab a transcript and e-mail the important parts to you. (I can't find your e-mail - mine's on my profile, so you can just use that.)

I guess that modal realism could be falsified if we managed to step outside the observable universe and find out how universes work in general. But until or unless we get that, the proposition that there are parallel but absolutely inaccessible universes cannot be tested. Simply showing that our universe works in thus-and-such a particular way doesn't resolve the problem of inaccessible parallel universes.

Quantum randomness is but one of several interpretations available, given the evidence. The other two (as I explained in Questions for Physicists, linked above) are, basically, a variant on modal realism where all possible mathematical expressions are real-live universes in themselves, and the "hidden variables" interpretation which postulates finer determinants which we are as-yet powerless to detect and measure. I'm a fan of the latter, but I can't meaningfully distinguish it from the other two, so I'm trying to remain agnostic (and it's wearing away at my determinism!). The important part is that these two other interpretations do away with the violation of logical necessity: the "many worlds" interpretation simply says that all possibilities are in fact actualities, and the hidden variables interpretation says that it's governed by finer logic we haven't yet discovered.

Your Bayesian expectations don't seem to take the anthropic principle into account: we can only have this discussion in universes in which we exist; we are having this discussion; therefore we must perforce be in such a universe, and the odds are simply immaterial (though an interesting academic exercise - just how lucky are we, I wonder?). Of course there are more ways for a thing to "not be" than for it to "be," yet here we are no matter the odds against it.

I saw your reply at THINK, though I don't remember linking to it. It's pretty much dead, but I responded just the same. As for "He Lives," I have to say that I think religious belief and general intelligence have next-to-nothing to do with each other; the correlation of unbelief with higher education notwithstanding, I try to treat people as individuals. Some of them disagree with me on metaphysical matters, but I've always seen that, even when I was a believer. I'm gonna go read your paradox article now (is this it?). Later!

12/10/09 23:02  

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