Is the Many-Worlds Interpretation truly deterministic?

[Daniel Valient]

I am just looking for an answer to this question--

Does the Many-Worlds Interpretation demand that every physically possible scenario has to be played out somewhere in the Multiverse? David Deutsch has told me that yes this is true (including absurd/ unlikely scenarios...although those would happen with less frequency)

And here is what Max Tegmark has said about Many Worlds--

"Things inconsistent with the laws of physics will never happen - everything else will. However, to cheer you up: even if some of your twins hold up gas stations, most of your twins certainly don't, given what I already know about your personality; it's important to keep track of the statistics, since even if everything conceivable happens somewhere, really freak events happen only exponentially rarely".

So that is my question. I would love to believe what someone posted earlier...that certain physically possible events WILL NOT happen in the multiverse, but that seems to be at odds with the strictly deterministic nature of this theory.

 

[mfb]

MWI is deterministic in terms of the evolution of the universe.

Every physically possible process happens in some branch, but the norm of branches where extremely "unlikely" things happen (like a broken glass reassembling) is negligible.

 

[Daniel Valient]

Okay, thanks for the response. And this is consistent with what people like Tegmark have said...
But I'm going to test the limits of what you've just said and ask you the same question that I asked David Deutsch...Is there a universal branch where George W. Bush and Bill Clinton get married? It seems like a silly question, but if absurd scenarios like that are actually physically taking place...it raises a million questions about ethics and the implications of living in a multiverse.
Even though the absurd universes make up a negligible minority of overall universes, those negligible universes are themselves verging on infinite and increasing exponentially. The universal timeline where the shattered glass spontaneously reassembles is not just one universe but an incalculable number of branching timelines wherein the glass reassembles in trillions of slightly different ways. The universe where George Bush and Bill Clinton get married is not just one universe but trillions of constantly branching timelines where every possible version of their relationship is destined to be played out...
So in that's sense, its not really a comfort to say that absurd/ highly unlikely scenarios are only happening to us in a small minority of universes, because that small minority of universes is actually an incalculably vast plethora of universes...(and incalculably vast numbers of "you"s and "me"s who are experiencing what is going on in those universes)

 

[Daniel Valient]

I keep going back and forth on mwi. The science seems to point to it being true...but my common sense tells me it doesn't add up (and of course my common sense is probably wrong...)

 

[mfb]

.Is there a universal branch where George W. Bush and Bill Clinton get married?

Sure.

Even though the absurd universes make up a negligible minority of overall universes, those negligible universes are themselves verging on infinite and increasing exponentially.

You cannot count them. And even if you could, it would not make sense.
And philosophical discussions are not the scope of this forum.

 

[Daniel Valient]

Sure.You cannot count them. And even if you could, it would not make sense.
And philosophical discussions are not the scope of this forum.

Okay then...here is a question that may belie my knowledge of the topic. But I have to ask--

If what we perceive as "normal events" make up the overwhelming share of multiversal timelines..does this mean that there are duplicative universes to ensure that "normal timelines" are in the majority...

Let me explain what I mean-- Assume there is one timeline where George W. Bush is married to Bill Clinton...that timeline then branches into EVERY POSSIBLE outcome that could arise from that relationship (the universes where they honeymoon in Maine, the universes where they honeymoon in NIagara Falls etc etc...) Everything that can possibly happen does happen.

Now let's look at an initial "normal" timeline where George W. Bush is married to Laura Bush...that timeline also branches into EVERY POSSIBLE outcome that could arise from that relationship (the universes where they honeymoon in Maine, the universes where they honeymoon in NIagara Falls so on and so forth)

Wouldn't the "absurd" universes and the "normal" universes have the exact same number of timelines (i.e. one timeline branch per physically possible event)?

The only thing I can think of that would change that ratio is if there are duplicative versions of the "normal timelines" i.e. there are several identical versions of that moment where George proposes to Laura for every one instance (or branch) where George proposes to Clinton...

Are there duplicative copies of universes in order to weight the multiverse towards "normality"? Or am I missing something more obvious here?

 

[Daniel Valient]

By the way, I would also be interested in hearing from people who believe in mwi but DON'T necessarily believe that absurd/ low density universes must be represented...
Have any of you mwi proponents taken that position?

 

[mfb]

does this mean that there are duplicative universes to ensure that "normal timelines" are in the majority...

No, it means you cannot count them, and even if you could it would not make sense. See my previous post.

"every possible outcome" is much more than what we would describe as individual outcomes for humans. "individual outcomes" are dominated by the level of individual atoms in different places.

By the way, I would also be interested in hearing from people who believe in mwi but DON'T necessarily believe that absurd/ low density universes must be represented...

The existence of "odd" branches is a direct consequence of MWI, it doesn't make sense to like (believe is the wrong word) one thing but don't believe in its consequences.

There is an approach to develop a different theory (not interpretation) called mangled worlds, which would introduce a physical process to remove those worlds.

 

[secur]

I keep going back and forth on mwi. The science seems to point to it being true...but my common sense tells me it doesn't add up (and of course my common sense is probably wrong...)

Trust your common sense

 

[Daniel Valient]

Trust your common sense

ha...yes perhaps I should. But there seem to be problems with all of the other Interpretations as well...
I think I need to take a second look at the Bohm/ pilot wave Interpretations...

 

[cosmik debris]

I wonder if it is like the path integral formulation of QM in that the multiple worlds which are close re-inforce each other and those that are radically divergent cancel out leaving the observer to observe the most likely universes forming the experience.

 

[PeterDonis]

Is there a universal branch where George W. Bush and Bill Clinton get married?

Assuming that this is physically possible, yes.

But a lot of other things in this branch are probably different from our branch as well. This is left out in virtually all discussions of this topic that I have seen; alternate branches are always talked about as though they are exactly like our branch except for one small change (or one small change plus the obvious implications of it--for example, obviously the same Bush and Clinton children would not exist in a branch where GWB married Bill). But the MWI does not say that; more precisely, the MWI does not require that such a branch--not just one where GWB and Bill marry, but one where they marry and everything else except that and the obvious consequences is the same as ours--is physically possible. It could be that any physically possible GWB-Bill marriage branch differs from ours in lots of other ways as well, going back not just to the meeting or even the births of GWB and Bill but hundreds or thousands of years or even more. It could be that in this hypothetical branch no one exists corresponding to Hillary Clinton (or Monica Lewinsky or Gennifer Flowers or any other of Bill's paramours); it could be that there isn't even a United States of America in this branch, or any office even close to President; it could be that GWB and Bill are not politicians and have life stories very different from the ones they have in our branch (even though they are DNA and personality identical); it could be that the entire history of Western civilization is different--perhaps male homosexuality has been the norm since the 5th century BC in this branch. We have no way of knowing without being able to model the microphysics of human beings and human history at a level many orders of magnitude more detailed than our current models.

Of course you could object that the people I was calling "GWB" and "Bill" in this hypothetical completely different branch don't really qualify for those labels (for one thing, it might not be physically possible for them to be DNA and personality identical to our versions). But that just means that the original premise, that there is a branch where GWB and Bill marry, is physically possible, was false--there might be no physically possible world in which two people that are close enough to our GWB and Bill to deserve those labels, marry. In other words, such claims might be drastically underestimating the extent to which what we see as contingent facts about people, like whom they are attracted to and whom they marry, are actually physically determined by the specifics of the world/branch in which they exist.

 

[Daniel Valient]

Assuming that this is physically possible, yes.

But a lot of other things in this branch are probably different from our branch as well. This is left out in virtually all discussions of this topic that I have seen; alternate branches are always talked about as though they are exactly like our branch except for one small change (or one small change plus the obvious implications of it--for example, obviously the same Bush and Clinton children would not exist in a branch where GWB married Bill)

But that's the thing...I think mwi does require this...For example I think that is required that right now, as I'm writing this, our universe is going to branch into a timeline where Bill Clinton suddenly decides that he is in love with Bush and jumps up to book a flight to Texas (or wherever GWB lives) As far as I can tell, Clinton's own personality and the previous nature of the Bush/ Clinton relationship would be immaterial. If determinism is real there would be a kind of “quantum insanity” which would force us to do ridiculous and irrational things.
That's the problem with mwi. We know that these things are impossible from a common sense perspective...but like mfb said earlier, determinism is kind of an all or nothing proposition
But the thing I wonder is...if human behavior arises from biology, biology arises from chemistry and chemistry arises from physics..etc...etc. Is some human behavior so ridiculous and/or counterproductive that it would effectively violate the laws of physics? I doubt it but I often wonder if any mwi proponents have ever explored this idea?

By the way I like your avatar...

 

[Daniel Valient]

I wonder if it is like the path integral formulation of QM in that the multiple worlds which are close re-inforce each other and those that are radically divergent cancel out leaving the observer to observe the most likely universes forming the experience.

are there any academic papers or writings on this theory? It seems like an interesting idea...

 

[PeterDonis]

If determinism is real there would be a kind of “quantum insanity” which would force us to do ridiculous and irrational things.

I don't see this at all. But in any case, the question whether it is physically possible for, say, Clinton and Bush to suddenly decide to get married tomorrow, is not really a question of quantum mechanics; it's a question of cognitive science, psychology, etc. And we certainly don't know anywhere near enough about those disciplines to be able to say that quantum superpositions play any role in our mental processes, much less that there are superpositions possible that would lead to "quantum insane" branch points such as you describe. So for MWI proponents to claim that there must be branches where such things take place seems to me to be going way beyond what the theory actually says.

Is some human behavior so ridiculous and/or counterproductive that it would effectively violate the laws of physics?

What do you mean by "effectively violate"? Nothing can violate the actual laws of physics, by definition. If we saw something that seemed to violate what we thought were the laws of physics, we would have to revise our understanding of the laws; we wouldn't say the laws were violated.

 

[atyy]

I keep going back and forth on mwi. The science seems to point to it being true...but my common sense tells me it doesn't add up (and of course my common sense is probably wrong...)

Whether MWI is sensible remains controversial, even according to proponents.
http://www.preposterousuniverse.com...ion-of-quantum-mechanics-is-probably-correct/
http://www.preposterousuniverse.com...y-worlds-interpretation-of-quantum-mechanics/
https://arxiv.org/abs/0712.0149

 

[cosmik debris]

are there any academic papers or writings on this theory? It seems like an interesting idea...

It may be similar to the mangled worlds idea mentioned above by mfb, but we must be careful here to not violate the charter. I am not suggesting this as a theory only as a way of thinking about things, this may be philosophy. The problem with all Quantum mechanical interpretations is that they all seem to be philosophy.

 

[Daniel Valient]

I don't see this at all. But in any case, the question whether it is physically possible for, say, Clinton and Bush to suddenly decide to get married tomorrow, is not really a question of quantum mechanics; it's a question of cognitive science, psychology, etc. And we certainly don't know anywhere near enough about those disciplines to be able to say that quantum superpositions play any role in our mental processes, much less that there are superpositions possible that would lead to "quantum insane" branch points such as you describe. So for MWI proponents to claim that there must be branches where such things take place seems to me to be going way beyond what the theory actually says.

Well, my common sense tells me your right but many of the experts say that that psychology doesn't really enter it...They would say that subatomic determinism overrides any psychological or social norms.

What do you mean by "effectively violate"? Nothing can violate the actual laws of physics, by definition. If we saw something that seemed to violate what we thought were the laws of physics, we would have to revise our understanding of the laws; we wouldn't say the laws were violated.

Yeah that's what I'm saying...mwi proponents say that everything happens somewhere in the multiverse...with the exception of events that violate the laws of physics. So I'm proposing that perhaps some human behavior is so counterproductive that it can not possibly happen. This human behavior would actually violate the laws of physics and would therefore not be allowed to happen under the mwi framework...

But unfortunately it's a pretty weak argument for several reasons. One reason is that we see bipolar/ schizophrenic doing absurd and counterproductive things on a regular basis. So we see that physics will allow counterproductive behavior to occur.

The other reason that it's a weak argument is because... even if there is an “emergent impossibility factor” (i.e. it so unlikely for me to say---gouge out my own eyes, from a rational/ commonsensical perspective that this event becomes effectively impossible... it may be irrelevant under the mwi framework because of recherché events like quantum tunneling and classically improbable subatomic activity.

Thats the main problem-- Quantum tunneling seems to indicate that extremely improbable subatomic interactions (and thus extremely improbable real world events) are inevitable under the mwi framework.

So the whole mystery of the mind/ body split may be irrelevant….Even if human logic is somehow able to override the determinism of mwi it wouldn't even matter in the face of absurd quantum physics. I may not want to poke out my own eyes but in trillions of universes my arm will involuntarily spasm and stab them out just the same…in some universes I will black out and when I come to my eyes will be gone…in some universes a pre-programmed robot will suddenly materialize out of the ether and force my arm to to perform the stabbing motion….
Determinism would always override our "free will"

 

[Daniel Valient]

It may be similar to the mangled worlds idea mentioned above by mfb, but we must be careful here to not violate the charter. I am not suggesting this as a theory only as a way of thinking about things, this may be philosophy. The problem with all Quantum mechanical interpretations is that they all seem to be philosophy.

Yeah that's what's amazing...after all these years, there is still is not an Interpretation which makes sense. Like David Deutsch has said, if mwi is not true then something REALLY WEIRD is going on...

 

[Daniel Valient]

Whether MWI is sensible remains controversial, even according to proponents.
http://www.preposterousuniverse.com...ion-of-quantum-mechanics-is-probably-correct/
http://www.preposterousuniverse.com...y-worlds-interpretation-of-quantum-mechanics/
https://arxiv.org/abs/0712.0149

Yeah there are so many problems with mwi but I'm still open to it because so many of my heroes seem to favor it...David Deutsch, Max Tegmark, Frank Tipler, Richard Feynman...these are some of the brightest minds of our time...not to mention household names in the world of physics like Neil DeGrasse Tyson, Stephen Hawking, Murray Gell-Mann etc etc
Then again there are many bright people who favor opposing Interpretations...but they definitely seem to be in the minority.

 

[PeterDonis]

many of the experts say that that psychology doesn't really enter it...They would say that subatomic determinism overrides any psychological or social norms.

Can you give some actual examples? By which I mean, actual textbooks or peer-reviewed papers that argue for this viewpoint and give evidence to support it? I know physicists say lots of things in pop science articles, TV shows, etc., but that's because they can get away with stating their personal opinions in such venues even if those opinions are not supported by the actual physical theories.

I'm proposing that perhaps some human behavior is so counterproductive that it can not possibly happen. This human behavior would actually violate the laws of physics

I don't think that whether a particular hypothetical human behavior is "productive" in human terms has any significant bearing on whether or not it violates the laws of physics. That seems to me to be just anthropomorphism.

I'm also not sure that you have understood my argument. I wasn't arguing that a multiverse branch in which GWB and Bill marry might violate the laws of physics because such behavior would be "unproductive", or even because it would be so far out of sync with their personalities as we know them. I was arguing that the idea that there could be a multiverse branch in which GWB and Bill married but everything else (except for direct consequences of that change) was exactly the same as our branch, might not be correct, because such a branch might not be physically possible; there might be no physically possible way for an alternate branch to evolve such that only that one thing changed from ours. And the more things are changed from our branch, the less reason we have to call the individuals that marry in that branch "GWB" and "Bill", because a significant part of the personal identity of those individuals is their history--the particular facts of the branch they exist in.

Perhaps another way of putting my objection is that, in order to imagine a branch in which GWB and Bill marry but nothing else changes, we need to know how to identify "GWB" and "Bill". What constitutes the personal identity of those individuals? Any MWI proponent who claims that we can do this purely based on our knowledge of quantum physics is, to put it bluntly, full of it. (AFAIK no MWI proponent claims this explicitly, but many of the claims they do make, if you went into the details, would, I suspect, turn out to implicitly assume that something like this is possible.) The question of what constitutes personal identity is not a question of physics, or at least not physics alone.

Quantum tunneling seems to indicate that extremely improbable subatomic interactions (and thus extremely improbable real world events) are inevitable under the mwi framework.

As I said before, this matters for our discussion here only if quantum superpositions turn out to play a significant part in determining what human beings do. But we have no evidence that this is the case. The only concrete speculation I'm aware of along these lines, Penrose & Hameroff's idea about quantum superpositions in microtubules, didn't pan out when it was tested, AFAIK. As far as we can tell, our brains are classical objects and can be described perfectly well by classical physics, which means that there are no significant quantum superpositions involved.

 

[secur]

MWI is far from proven, it's not even fully defined yet. Problems exist in accounting for Born probabilities and the actual experience of the experimenter, which can bring in difficult questions involving exactly how consciousness is supposed to "branch". In fact a recent study showed that MWI may possibly be twaddlish.

 

[bhobba]

Yeah there are so many problems with mwi but I'm still open to it because so many of my heroes seem to favor it...David Deutsch, Max Tegmark, Frank Tipler, Richard Feynman...these are some of the brightest minds of our time...not to mention household names in the world of physics like Neil DeGrasse Tyson, Stephen Hawking, Murray Gell-Mann etc etc

Hmmmm.

Many of those most definitely do NOT favor MWI - they favor consistent histories.

It is true they are open to it because CH has been described as MW without the MW.

Thanks
Bill

 

[vanhees71]

It's an interesting question what Feynman was thinking about "interpretation". I think he'd be very critical and refer to "shut up and calculate". I can't help it to find this the wisest advice ever given concerning this rather philosophical side. I can't however agree with his criticism against Bell whose work precisely anabled a clearly physical approach, but my personal conclusion is that indeed the empirical facts concerning this work more and more solidifies the minimal probabilistic interpretation. There are probabilities, and that's it. There's no more than that behind QT, and as it seems that's how nature can be described as real and not somehow more.

 

[Jilang]

Please can you supply evidence that Feynman said to "shut up and calculate"?

 

[vanhees71]

Intro Chapter of the Feynman Lectures, vol. III. It's anyway a very good book to start with QM.

 

[Mentz114]

Yeah that's what's amazing...after all these years, there is still is not an Interpretation which makes sense. Like David Deutsch has said, if mwi is not true then something REALLY WEIRD is going on...

No ... the problem that drives the invention of mwi is how the universe chooses between the eigenvalues of an operator. This ignores the fact that operators, eigenvalues and their associated probabilities are mathematical abstractions. In the real world there is dissipation, non-unitary evolution, absence of superposition and other noise that let's the outcome be decided by the current state of the universe - at the time and place of the measurement.

Much less weird that Clinton marrying Bush.

 

[Jilang]

Intro Chapter of the Feynman Lectures, vol. III. It's anyway a very good book to start with QM.

I'm puzzled then as Mermin doesn't seem so clear on it.
http://scitation.aip.org/content/aip/magazine/physicstoday/article/57/5/10.1063/1.1768652

 

[nikkkom]

But that's the thing...I think mwi does require this...For example I think that is required that right now, as I'm writing this, our universe is going to branch into a timeline where Bill Clinton suddenly decides that he is in love with Bush and jumps up to book a flight to Texas (or wherever GWB lives) As far as I can tell, Clinton's own personality and the previous nature of the Bush/ Clinton relationship would be immaterial. If determinism is real there would be a kind of “quantum insanity” which would force us to do ridiculous and irrational things.

I don't understand your fixation on Bush+Clinton. There are way more weird things which should be happening, with very very very low probability, in MWI. Such as cups of water spontaneously freezing, all dice rolls on the entire Earth producing only 6 for thousands of years on end, etc. All this is technically possible. All this will virtually certainly not happen to any of us, you can be sure of it.

 

[PeterDonis]

cups of water spontaneously freezing, all dice rolls on the entire Earth producing only 6 for thousands of years on end, etc.

The same comment I made previously applies here: these things are only relevant for the MWI if quantum superpositions play a meaningful role. Do they? I don't see how they do for die rolls. Cups of water spontaneously freezing, possibly, but I'm doubtful.

 

[DennisN]

I wonder if it is like the path integral formulation of QM in that the multiple worlds which are close re-inforce each other and those that are radically divergent cancel out leaving the observer to observe the most likely universes forming the experience.

You may find this PF thread about a paper from 2014 interesting: Many Interacting Worlds.

 

[vanhees71]

I'm puzzled then as Mermin doesn't seem so clear on it.

http://scitation.aip.org/content/aip/magazine/physicstoday/article/57/5/10.1063/1.1768652

I'm not sure whether Feynman ever verbatim wrote about "shut up and calculate", but if you read the introductory chapter on QM, where he discusses carefully the double-slit experiment with particles and its physical meaning, you can summarize his view on "interpretation" by this phrase, and I think that's the right attitude. As with any other mathematical model about the world there is a mathematical formalism (in QM there's a Hilbert space with operators acting on vectors in this space representing states (statistical operator) and observables) and a minimal interpretation of it to apply it to observations about nature (probabilities, expectation values, S-matrix elements in QFT and so on), and that's it. From a physics point of view you don't need anything more, let alone some hokus pokus like many worlds or Bohm-de Broglie trajectories and the like all of which are not observable by declaration and thus not part of physics.

According to QT there is no answer to the question, why in an experiment on a specific system described by quantum theory the outcome is the observed one. There are only probabilities for that outcome given the preparation (state) of the system. You can test this prediction by repeating the observation very often on independently and equally prepared systems, and so far the predictions of QT were always found to be very accurate, and that's why QT is taken as the best and most comprehensive theory we have to describe nature.

That doesn't mean that QT is the last word about how to model nature mathematically. Maybe one day one finds a discrepancy with the predictions of QT, and one has to build a better theory. That's how science works, and not some philosophical speculations that cannot be anwered by careful observation and quantitative measurements.

As the example of Bell's work show, it can still happen, that a purely philosophical speculation like the idea about "reality" set up in a quite vague sense by Einstein, Podolsky, and Rosen in their no famous paper (although Einstein himself didn't like this paper too much, and he has written a much better one as a single author later: A. Einstein, Quantenmechanik und Wirklichkeit (Quantum Mechanics and Reality), Dialectica 2, 320 (1948)) can be sharpened to a scientific question that can be answered by observation and measurement and thus becomes part of the exact sciences: Bell thought about local deterministic hidden-variable theories and derived an inequality for certain correlation functions that are violated by the predictions of (minimally interpreted!) quantum theory, and as many experiments show in the meantime, this inequality is violated with an amazing statistical significance and (at the same significance!) quantum theory has been confirmed.

As I said above, this doesn't mean that QT is the final answer, but a worldview a la EPR, i.e., that nature may be after all describable by a deterministic local hidden-variable theory is ruled out. There may be nonlocal ones, but so far nobody has been able to formulate a convincing one that is as successful as QT.

 

[stevendaryl]

No ... the problem that drives the invention of mwi is how the universe chooses between the eigenvalues of an operator. This ignores the fact that operators, eigenvalues and their associated probabilities are mathematical abstractions. In the real world there is dissipation, non-unitary evolution, absence of superposition and other noise that let's the outcome be decided by the current state of the universe - at the time and place of the measurement.

That seems false to me. Do you have a reference that makes that claim?

[added later]
I think there is general agreement that decoherence is responsible for destroying interference patterns, and making it impossible for a subsystem to be in a superposition of states. But I don't think there is any consensus that environmental effects select one possibility for the result of a measurement over another.

 

[stevendaryl]

The same comment I made previously applies here: these things are only relevant for the MWI if quantum superpositions play a meaningful role. Do they? I don't see how they do for die rolls. Cups of water spontaneously freezing, possibly, but I'm doubtful.

I don't understand your remarks. What, exactly, are you doubtful about? Are you still talking about the issue of whether very weird outcomes actually happen in MWI?

 

[stevendaryl]

According to QT there is no answer to the question, why in an experiment on a specific system described by quantum theory the outcome is the observed one. There are only probabilities for that outcome given the preparation (state) of the system. You can test this prediction by repeating the observation very often on independently and equally prepared systems, and so far the predictions of QT were always found to be very accurate, and that's why QT is taken as the best and most comprehensive theory we have to describe nature.

Perhaps it is getting off-topic to raise this objection to what you're saying, but my issue with the standard formulation of quantum theory is not about the irreducible probabilities---it's about the fact that probabilities are described as probabilities for measurement results. If a measurement is a process describable by ordinary physics (and thus, by QM), then it should be possible to reformulate the Born rule so that it doesn't mention measurements at all.

Suppose (for instance) that a measurement of an observable O on a microscopic system can be described as an interaction between the microscopic system and a macroscopic measuring device D such that different values of O lead to different macroscopically distinguishable states of D. Such an interaction would probably involve irreversibility. So a candidate for a replacement of the Born rule that doesn't single out measurement as special might be something along the lines of:

"When a microscopic system interacts with a macroscopic system to cause an irreversible change in the latter, then ..."

But that doesn't sound very fundamental, either. What happens to a macroscopic system should be derivable from what happens to microscopic systems, using the usual techniques of statistical mechanics for dealing with huge numbers of particles.

So ultimately, it seems to me that there should be a formulation of QM that doesn't mention anything about macroscopic concepts such as measurements or expectation values or irreversibility. Those statements should, in my opinion, be derivable from statements about what goes on at a microscopic level. And pure QM doesn't have such a description.

 

[vanhees71]

But it is precisely what quantum statistics does for you! It describes the behavior of classical, macroscopic systems in terms of the "relevant" macroscopic observables and explains, why these quantities behave in almost all case as described by classical physics. Classicality is the result of a sufficiently coarse-grained description. There is no other way to observe nature in its microscopic details than to use "amplification" and "measurement devices" that are macroscopic to make these observables comprehensible finally to our senses.

 

[stevendaryl]

But it is precisely what quantum statistics does for you! It describes the behavior of classical, macroscopic systems in terms of the "relevant" macroscopic observables and explains, why these quantities behave in almost all case as described by classical physics.

I don't think so. If macroscopic phenomena such as measurements are described in terms of microscopic phenomena, then the axioms of quantum mechanics should be expressible solely in terms of the microscopic phenomena. So there would be no need for an axiom saying "A measurement results in an eigenvalue with a probability given by..."

 

[A. Neumaier]

If a measurement is a process describable by ordinary physics (and thus, by QM), then it should be possible to reformulate the Born rule so that it doesn't mention measurements at all.

So ultimately, it seems to me that there should be a formulation of QM that doesn't mention anything about macroscopic concepts such as measurements or expectation values or irreversibility. Those statements should, in my opinion, be derivable from statements about what goes on at a microscopic level. And pure QM doesn't have such a description.

Such an improved formulation was given here.

My thermal interpretation is fundamental in the sense you require. It is meaningful without mentioning measurement at all, and implies the Born rule in the cases where the latter is appropriate. It is fully compatible with statistical mechanics (the theory of macroscopic implications of quantum mechanics, including irreversibility), from which it was in fact abstracted. And statistical mechanics is also the discipline in terms of which real measurement processes with real detectors can be analyzed. Indeed, to design good detectors one uses statistical mechanics and not the Born rules!

The thermal interpretation doesn't contain anything essentially new - it just places the emphasis in a way that makes the obvious more obvious instead of (as traditional interpretations do) placing counterintuitive axioms such as Born's rule (which are valid only in special contexts) into the center of attention.

 

[stevendaryl]

Such an improved formulation was given here.

No offense, but I don't agree that your reformulation solves the problem. Basically, you're saying that if we have a large system of many, many particles, then macroscopic variables (such as field averages) can have well-defined values. But that seems to me to be a matter of choosing a setting where the peculiarities of quantum mechanics are swamped out. It's not an explanation. You can still have quantum mechanics of a small number of particles; for example, in the EPR experiment. QM makes definite predictions about observations for such systems, and those predictions don't require any kind of thermal limit.

 

[A. Neumaier]

No offense, but I don't agree that your reformulation solves the problem. Basically, you're saying that if we have a large system of many, many particles, then macroscopic variables (such as field averages) can have well-defined values. But that seems to me to be a matter of choosing a setting where the peculiarities of quantum mechanics are swamped out. It's not an explanation. You can still have quantum mechanics of a small number of particles; for example, in the EPR experiment. QM makes definite predictions about observations for such systems, and those predictions don't require any kind of thermal limit.

Note: Expectation values are just values with an objective meaning in each state, whether macroscopic or microscopic. Expectations of a macroscopic observable are measurable by a single macroscopic measurement. Unlike measurements, expectations are part of the standard theory (shut-up-and-calculate). If you see the need to ban expectation values from a fundamental description you would also need to ban observables, and the theory would become impossible to formulate.

QM makes indeed lots of predictions about expectations of observations for microscopic systems, and those predictions don't require any kind of thermal limit. These expectations are correctly described by the thermal interpretation, even for microscopic systems. That the motivation of the interpretation comes from statistical mechanics doesn't mean that the interpretation itself is limited to macroscopic systems.

 

[vanhees71]

I don't think so. If macroscopic phenomena such as measurements are described in terms of microscopic phenomena, then the axioms of quantum mechanics should be expressible solely in terms of the microscopic phenomena. So there would be no need for an axiom saying "A measurement results in an eigenvalue with a probability given by..."

I don't understand what you want. The natural sciences are about observations/measurements of nature. It's not about fairy tales concerning some "underlying truth", or however you want to name it. Quantum statistics is by the way nothing else than the application of the quantum-theoretical formalism to macroscopic objects, i.e., it delivers in a scientific sense what you want, namely the understanding of macroscopic behavior from the underlying fundamental/microscopic dynamics.

 

[stevendaryl]

I don't understand what you want.

A formulation of quantum mechanics in terms of microscopic properties, such that the macroscopic rule--"When you measure an observable, you get an eigenvalue of the corresponding operator with a probability given by ..."--is derivable, rather than postulated. I thought that's what I said.

 

[vanhees71]

The question is derivable from what, and if you find such a formulation, what's the advantage compared to the "traditional" formulation which starts from what's really measured in the lab?

 

[stevendaryl]

The question is derivable from what, and if you find such a formulation, what's the advantage compared to the "traditional" formulation which starts from what's really measured in the lab?

What does "advantage" mean, here? Science was created to understand phenomena--light, planetary motion, properties of gases and liquids, the behavior of substances when they interact---that exist independent of any lab. Labs are invented to help get more information about the world, but the world and its phenomena don't depend on labs for their existence. Nuclear processes in stars work the same way even when there are no nuclear physicists around.

I can certainly understand the point of view that the only thing that is important for scientists is to explain the observations of scientists, but I think that's a sterile, solipsistic view of science. Nobody becomes a scientist with that interpretation of science in mind---that the point of science is to explain what happens in science labs. They become scientists because they are curious about what goes on outside the lab.

 

[A. Neumaier]

Nuclear processes in stars work the same way even when there are no nuclear physicists around.

But nothing ever is measured then.

"When you measure an observable, you get an eigenvalue of the corresponding operator with a probability given by ..."--is derivable, rather than postulated.

See the derivation in Section 10.5 (p.239) of my online book (version v2).

 

[nikkkom]

The same comment I made previously applies here: these things are only relevant for the MWI if quantum superpositions play a meaningful role. Do they? I don't see how they do for die rolls. Cups of water spontaneously freezing, possibly, but I'm doubtful.

MWI says that there is no collapse, ever. When you open the box, cat doesn't become dead or alive. Instead, you are now entangled with the cat's state, and both states of "I see dead cat and feel depressed" and "I see live cat and feel happy" exist in superposition.

IOW, MWI says that every possibility which (like cat state) arises from quantum superposition, is realized. And presumably, fair dice rolls depend on past history of the dice cubes and the person throwing it, and there is more than enough variability in their past that every result of dice roll result is possible, and therefore, according to MWI, every of those possibilities is realized in some branches.

 

[Mentz114]

That seems false to me. Do you have a reference that makes that claim?

I think there is general agreement that decoherence is responsible for destroying interference patterns, and making it impossible for a subsystem to be in a superposition of states. But I don't think there is any consensus that environmental effects select one possibility for the result of a measurement over another.

What else can it be ? Are you proposing that something that something outside the universe universe is affecting this ?

I've heard of thinking outside the box but come on ! That is not physics.

 

[stevendaryl]

What else can it be ? Are you proposing that something that something outside the universe universe is affecting this ?

I'm not proposing anything. QM does not specify how one alternative is chosen out of a set of possibilities. You seem to be claiming that it does, and I think that's false.

 

[stevendaryl]

I'm not proposing anything. QM does not specify how one alternative is chosen out of a set of possibilities. You seem to be claiming that it does, and I think that's false.

I should say that it's not part of standard mechanics. To quote Bill Hobba from this thread:
https://www.physicsforums.com/threads/decoherence-and-standard-formalism.890882/#post-5604515

there are 3 parts to the measurement problem.

1. The problem of non observance of interference
2. How the preferred basis emerges.This is why, for example, classical objects nearly always have a definite position
3. How an improper mixed state becomes a proper one.

The first 2 is explained by decoherence, the third some interpretations simply assume, while others explain.

The meaning of "how an improper mixed state becomes a proper one" is the issue of how one possibility is selected out of a set of possibilities. It is not explained by decoherence or environmental effects. Or at least, there is no consensus that it is.

 

[vanhees71]

This argument goes in circles. There is the state of a quantum system, described by a statistical operator. The state is called pure if the statistical operator is a projection operator otherwise it's called a mixed state. It is impossible to distinguish between what you call proper vs. improper mixed state. We have clarified this several times now.