Many Worlds Interpretation and act of measuring

[Ilja]

What is meant by 'exists physically' is likely debatable by philosophers. But they are part of that interpretation 100% for sure.

Its a weird theory - too weird for me. But we discuss science here - not the level of weirdness - it may well be true. If you don't like it you are in good company - I don't - but one must keep an open mind. If it's too weird for you move on - check out some other interpretation. Once you understand QM better you can return to it with a better appreciation of the issues its trying to resolve as well as the very elegant, but weird, way it does it.

I disagree that one must keep an open mind about every piece of nonsense. The interpretation claims that the only thing which really exists is a wave function - a function on the space of all imaginable universes. I observe only one universe. So, even if there would be many different, this would be at least incomplete.

To construct its "many worlds", it uses decoherence, but decoherence presupposes some subdivision into subsystem. Because without a restriction to subsystems there is no decoherence. Nobody explains where this subdivision comes from.

The very interpretation contradicts common sense, but to "derive" the Born rule it relies on common sense - because this is what is Bayesian probability based on. Common sense, which is based on the assumption, that we will in future, as well as now, observe only a single universe, and that the problem of rational thinking is to find out which one.

It remains to explain, why this "interpretation" is that popular. It seems to me, that this is simply the most degenerate example of what I name "mathematical mysticism". The problem here is the positivistic rejection of the discussion of philosophy/metaphysics. Self-contradictory, because it is itself philosophy, but self-defending, because it forbids discussions that criticize it (as philosophy). But, because philosophy and interpretation is a natural part of natural philosophy (the original name of physics), the result of positivistic physics will not be physics without metaphysics but physics with bad metaphysics. It is easy to predict, which type of metaphysics wins here: The one which can less than any other be accused of "containing metaphysics". This is the mystification of the mathematics of the existing theory. Once the mathematics of the theory are the part which is at least connected with observation, nobody can argue that all these equations are "metaphysics" or "philosophy". So you are free to mystify them. The equations are not simply equations which describe, approximately, the results of clock measurements, no, they define spacetime itself. The wave function is not simply a not well understood device to compute probabilities, no, they are reality itself. Some different philosophical objects or principles should not exist, because they are philosophical. So, once GR has solutions with closed causal loops which violate causality, we have to throw away causality. Some hidden preferred global time, which could easily prevent causal loops in a Lorentzian interpretation of GR, is an additional structure, thus, anathema. Some single universe, the one where we live in, which could be easily introduced like in de Broglie-Bohm theory, is an additional, new structure, thus, anathema.

Why this is not simply one, possibly unfortunate but who knows, choice of metaphysics, but bad metaphysics? Simply because it is the most inert one, the one which prevents any progress toward a more fundamental theory. For a very simple reason: A new theory needs something new - new structures, new equations, new metaphysics. These new concepts should be, of course, compatible with the existing theory, but have to go beyond it. So, there will be not only a new theory, but also a new interpretation of the old one - the interpretation, where it is the limit, the approximation of the new theory. And this will be an interpretation containing something new, something which is not part of the equations of the old theory. And one needs, together with the new interpretation, new problems - the problems which suggest how to modify the approximate equations of the new theory, which we already knew, to obtain the new, more fundamental equations. The way we can identify these problems today is also predictable: They will appear as metaphysical conflicts of the interpretation with some other, independent metaphysical principles. So, we need exactly those things which are abhorrent to mathematical mysticism.

Just as an aside when I first leant of this interpretation I thought you would have to have rocks in your head to believe it - its nearly as bad as conciousness causes collapse. But slowly, oh so slowly, from discussion here, further reading and thinking about this issues, I grew to appreciate what it does and what it resolves. I got Wallace's book on it and saw just how beautiful mathematically it is. It even links to other interpretations like Consistent Histories, so a study of each deepens understanding of the other. In science having an open mind is very very important. That's not to say you shouldn't have an opinion - that's just as important - but it must be an informed opinion.

So, please, tell me this hidden secret - I have yet been unable to see even a single piece of beauty - mathematical or otherwise - in this interpretation. As well as in inconsistent histories.

 

[Ilja]

I haven't worked through the paper, but doesn't having an objective wave function collapse imply nonlocal interactions (according to Bell's theorem)?

Every realistic/causal interpretation implies it, so what?

 

[bhobba]

I disagree that one must keep an open mind about every piece of nonsense. The interpretation claims that the only thing which really exists is a wave function - a function on the space of all imaginable universes. I observe only one universe. So, even if there would be many different, this would be at least incomplete.

Well you believe its nonsense. Fair enough. But I am sure you know as well as I do nonsense is in the eye of the beholder.

To construct its "many worlds", it uses decoherence, but decoherence presupposes some subdivision into subsystem. Because without a restriction to subsystems there is no decoherence. Nobody explains where this subdivision comes from.

The branching decooherence theorem on page 93 of Wallaces book may have something to do with it. But it involves studying the book with an open mind.

As I mentioned before one can define a history without reference to measurement, arbitrary division etc etc and use that to bootstrap it. Consistent Histories is similar.

So, please, tell me this hidden secret - I have yet been unable to see even a single piece of beauty - mathematical or otherwise - in this interpretation. As well as in inconsistent histories.

The secret of why I find it beautiful? There is this debate about nature vs nurture - me I believe its a bit of both - but who knows.

Thanks
Bill

 

[Quantumental]

to those of you discussing if atoms really touch: please take it to another thread

 

[stevendaryl]

This "theory" is hardly pseudoscience, it is pure FANTASY, it doesn't exist in reality. This is the result of trying to understand quantum mechanics, In a few years who created this crap will be ashamed. You're only discussing it because "mathematically" is beautiful, but in reality is pure bollocks.

To me, MWI is not so much a theory as an inevitable consequence of QM. We have plenty of evidence that electrons, atoms and molecules can be a superposition of states, because we can calculate and measure the interference effects. MWI to me is simply denying that there is a cutoff between microscopic systems, which obey quantum mechanics and can be in superpositions, and macroscopic system. It's the assumption that QM applies to everything, no matter how large.

To me, it seems that any alternative to MWI amounts to assuming without evidence a limitation to quantum mechanics. It assumes without any evidence that at some quantum mechanics is wrong.

 

[stevendaryl]

I disagree that one must keep an open mind about every piece of nonsense. The interpretation claims that the only thing which really exists is a wave function - a function on the space of all imaginable universes. I observe only one universe. So, even if there would be many different, this would be at least incomplete.

The way I see it is that the conclusion that macroscopic objects (cats, humans, the solar system, the universe) can be in quantum superpositions amounts to just assuming that quantum mechanics applies to those objects. We have plenty of evidence that QM applies to small objects (electrons, atoms, molecules), and we have zero evidence that there are any new effects or new limitations that would prevent it from applying to larger objects.

Your reasoning is something along the lines of:

1. Theory X predicts phenomenon Y.
2. I don't see Y.
3. Therefore X is wrong.

That's just not a valid argument, although it certainly is appealing. What you would need to make it valid is an additional assumption:

1. Theory X predicts phenomenon Y.
2. Theory X predicts that under circumstance Z, we would see evidence of Y.
3. In circumstance Z, we don't see evidence of Y.
4. Therefore X is wrong.

Objecting to MWI because you don't see these macroscopic superpositions is sort of like objecting to the theory that Nepal exists because I've never seen it. I've never had an opportunity to see it.

The way science works, it seems to me, is that you only observe a tiny amount of phenomena in the universe--the universe is too vast for us to observe more than an infinitesimal part of it. But based on the phenomena that we observe, we formulate theories, and we rigorously test them. At some point, we become confident that they apply even in circumstances where they have never been tested. We have confidence that Newton's physics works as well on Pluto as it does on Earth. Of course, we don't have proof of that, but we have no reason to believe otherwise.

To me, the belief that quantum mechanics applies to macroscopic objects is the same sort of case.

 

[Quantumental]

stevedaryl: then how do you explain the factorization problem?

 

[stevendaryl]

stevedaryl: then how do you explain the factorization problem?

I don't have an explanation for it. I'm just saying that

1. There is no good reason to think that QM does not apply to macroscopic systems.
2. So something like MWI is true unless we discover some corrections to quantum mechanics.

To me, the stuff about trying to understand how probabilities arise in MWI is not a matter of fanciful speculation. It's an attempt to come to grips with the possibility that our theory (QM) is actually true.

I understand that what is meant by QM already includes distinctions between system and observer, between unitary evolution and measurement processes. However, the role of these special cases can be made minimal. You could, in keeping with Copenhagen, consider the entire history of the universe to be a single quantum experiment, and the only measurement is at the end, when someone is trying to put together a "history of the universe" right before the Big Crunch (if that happens--I guess they are now pretty certain it won't).

 

[Quantumental]

I don't have an explanation for it. I'm just saying that

1. There is no good reason to think that QM does not apply to macroscopic systems.
2. So something like MWI is true unless we discover some corrections to quantum mechanics.

This is blatantly wrong. You can interpret the delay-erasure experiment, quantum pigeons etc. to imply that quantum mechanics is explained by retrocausality. This seems to be implied by the lack of direction in time too. You got no reason to favour MWI over this.

The factorization problem + born rule problem implies that QM does *not* imply MWI.

 

[atyy]

This is blatantly wrong. You can interpret the delay-erasure experiment, quantum pigeons etc. to imply that quantum mechanics is explained by retrocausality. This seems to be implied by the lack of direction in time too. You got no reason to favour MWI over this.

The factorization problem + born rule problem implies that QM does *not* imply MWI.

But do you have a retrocausal theory that works?

 

[TrickyDicky]

I don't have an explanation for it. I'm just saying that

1. There is no good reason to think that QM does not apply to macroscopic systems.
2. So something like MWI is true unless we discover some corrections to quantum mechanics.

IMHO your premise 1. just generalizes your own difficulties to even consider that QM might be incomplete/wrong so it isn't valid as a scientific assumption, and hinders further discussion.

 

[bhobba]

But do you have a retrocausal theory that works?

The transactional interpretation maybe?

Thanks
Bill

 

[Quantumental]

But do you have a retrocausal theory that works?

I don't. I know several people are working on assembling such theories (Huw Price, Ken Wharton, Matthew Leifer, Yakir Aharanov etc.). Some have even extended it to MWI (Lev Vaidman).
But it is what nature seems to imply in several experiments.

Similarly David Deutsch's conviction of MWI which stems back to the time he concieved of the qubit (mid 1980s). He got the idea of the speed-up being in parallel with a separate world. Today we *know* this is not the case, as has been explained thoroughly by Scott Aaronson, Andrew Steane and Michael Cuffaro. So the original motivation for MWI has been refuted.

But your own (as well as others) belief in MWI seems motivated by the simplicity of the idea that we just extend the idea of the superposition and wavefunction to entail the univere as a whole. But how would that work? There is nothing external to the universe, hence nothing to decohere it. There is also no explanation of fundamental ontology in MWI. This is where David Wallace is still struggling to come up with some deeper ontology than the wavefunction which goes far beyond the quantum formalism as is explained by Jeffrey Barrett (author of the standard entry of Everett) in this paper page 36: http://www.socsci.uci.edu/~jabarret/bio/publications/everett4.pdf
This again enters the territory of the problem of factorization too. You yourself accept that there is no solution to this at this present time, yet you don't seem troubled by it. I have to ask: Why not?

Why not just accept for instance de-Broglie Bohm then? Sure it has problems with non-locality, but it's no worse than factorization, and it does seem to be what nature tell us. Particles moving in the pattern of waves. It has no probability problems like MWI does...Or as mentioned retrocausality as several experiments seem to suggest.. Why blindly favour MWI?

 

[bhobba]

The factorization problem + born rule problem implies that QM does *not* imply MWI.

I think you are a bit confused between problem and definite refutation. Both those issues are controversial and not generally considered to be the theory killer you think it is - as I think has been pointed out to you many times.

Thanks
Bill

 

[Quantumental]

I think you are a bit confused between problem and definite refutation. Both those issues are controversial and not generally considered to be theory killer you think it is - as I think has been pointed out to you many times.

Until they have been solved they are indeed killers and is cited as the main reason why the majority of realist quantum foundation experts reject MWI. It's not just my personal opinion.

 

[TrickyDicky]

But do you have a retrocausal theory that works?

I'm pretty sure there isn't or we'd know. But that is the case with MWI, that it just doesn't work, not even the way Copenhagen works being at least honest about it's limits in an upfront way(Heisenberg cut and nonunitary collapse).
Even disciples of Zurek like Jess Riedel admit MWI doesn't work. The reason we
are even discussing it is because is so popular, but that fact belongs to sociology rather than physics.

 

[bhobba]

Until they have been solved they are indeed killers and is cited as the main reason why the majority of realist quantum foundation experts reject MWI. It's not just my personal opinion.

Again you are confused between an issue that needs clarification and an actual problem. For example I gave a possible way out of the factorisation problem as explained by vacuum fluctuations. And its not generally accepted that Wallace doesn't derive the Born Rule - I think he does - but there is a lot of debate about it.

Thanks
Bill

 

[Quantumental]

Again you are confused between an issue that needs clarification and an actual problem. For example I cave a possible way out of the factorisation problem as explained by vacuum fluctuations.

Then you have to flesh it out to a real explanation, otherwise it's barely an idea.

And its not generally accepted that Wallace doesn't derive the Born Rule - I think he does - but there is a lot of debate about it.

Wrong, most people don't think he has succeeded. It's mostly Oxfordians who accept the derivation to some extent. There have been tons of papers arguing against it (Alastair Rae, Huw Price, Adrian Kent, David Albert etc.), even amongst MWI supporters it is highly controversial (Jacques Mallah, Eliezer Yudkowsky, Robin Hanson etc.)

 

[stevendaryl]

IMHO your premise 1. just generalizes your own difficulties to even consider that QM might be incomplete/wrong.

That statement couldn't be more incorrect. I don't have any trouble considering the possibility that QM might be completely wrong. It's just that there is absolutely no evidence for it being wrong.

 

[stevendaryl]

This is blatantly wrong.

No, it's not. I said that there is absolutely no evidence that QM fails when applied to macroscopic objects. That's true.

You can interpret the delay-erasure experiment, quantum pigeons etc. to imply that quantum mechanics is explained by retrocausality.

I didn't say otherwise.

 

[bhobba]

Then you have to flesh it out to a real explanation, otherwise it's barely an idea.

The point is that argument can be reversed. Its an issue that needs fleshing out.

Wrong, most people don't think he has succeeded. It's mostly Oxfordians who accept the derivation to some extent. There have been tons of papers arguing against it (Alastair Rae, Huw Price, Adrian Kent, David Albert etc.), even amongst MWI supporters it is highly controversial (Jacques Mallah, Eliezer Yudkowsky, Robin Hanson etc.)

And you know this precisely how? What survey (of physicists and mathematicians - not philosophers like Huw Price) have you done to know that?

Thanks
Bill

 

[stevendaryl]

I'm pretty sure there isn't or we'd know. But that is the case with MWI, that it just doesn't work, not even the way Copenhagen works .

The way I see it, there is no difference between MWI and Copenhagen, other than where you draw the boundary of what the "system" is.

 

[stevendaryl]

The factorization problem + born rule problem implies that QM does *not* imply MWI.

I'm speaking a little loosely. QM by itself, with no additional assumptions implies macroscopic superpositions. That seems inevitable to me. If you allow macroscopic superpositions, then you're 99% of the way to MWI.

 

[TrickyDicky]

The way I see it, there is no difference between MWI and Copenhagen, other than where you draw the boundary of what the "system" is.

That's like saying there is no difference between a living person and a corpse other than where you draw the boundary between life and death.
The distinction you mention is capital.

 

[Quantumental]

And you know this precisely how? What survey (of physicists and mathematicians - not philosophers like Huw Price) have you done to know that?

Well you're the one that stated that it's generally accepted that he did derive it, so I can ask the same to you. I am going by the papers I have come across. I am completely open to being wrong if you can supply more papers accepting his derivation than I just mentioned of people not accepting it. And I don't see why you exclude philoophers of physics who got the same mathematic credentials. This is afterall very philosophically loaded in the firt place.

 

[bhobba]

The way I see it, there is no difference between MWI and Copenhagen, other than where you draw the boundary of what the "system" is.

I tend to agree with that - except I would say it was what many call Copenhagen done right - Consistent Histories. The only difference is interpreting what a history is.

Thanks
Bill

 

[stevendaryl]

I'm speaking a little loosely. QM by itself, with no additional assumptions implies macroscopic superpositions. That seems inevitable to me. If you allow macroscopic superpositions, then you're 99% of the way to MWI.

The counterargument that decoherence implies there ARE no macroscopic superpositions is, I think, an argument about semantics. Decoherence doesn't get rid of superpositions, it just makes it where, FAPP (For All Practical Purposes), we can ignore macrocroscopic superpositions, since interference between them is unobservable. Or maybe a different way of saying it is that if you start with a superposition of "Dead cat + Live cat", very rapidly, the situation changes to a superposition of "The Earth with a dead cat + The Earth with a live cat" and the "split" goes on to infect the entire universe.

That doesn't mean there are no macroscopic superpositions, it means such superpositions necessarily involve the entire accessible universe.

 

[Quantumental]

I'm speaking a little loosely. QM by itself, with no additional assumptions implies macroscopic superpositions. That seems inevitable to me. If you allow macroscopic superpositions, then you're 99% of the way to MWI.

I disagree because quantum mechanics itself is completely agnostic about the wavefunction itself. It doesn't say that the wavefunction exists. And all our experiments to date suggest there is in fact only 1 outcome and one world.

 

[TrickyDicky]

It's just that there is absolutely no evidence for it being wrong.

I said wrong or incomplete and there is plenty of evidence to consider the latter, think of all the peoplee working on Quantum gravity.
But the key point is that you cannot convert your own opinión about evidence (or lack of) about The status of QM in a logical premise to conclude that MWI must be Right. It is just not serious in a scientific Forum.

 

[bhobba]

And its not generally accepted that Wallace doesn't derive the Born Rule - I think he does - but there is a lot of debate about it.l

Well you're the one that stated that it's generally accepted that he did derive it, so I can ask the same to you.

Hmmmm. English was not my best subject, I was MUCH better at math - but I don't think that's what I said.

Thanks
Bill