Is the Many-Worlds Interpretation truly deterministic?

[Mentz114]

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.

This is getting off-topic. We've had this discussion before and we disagree deeply on this issue.

 

[stevendaryl]

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.

I don't agree with your "clarification", but if you're happy with it, fine. Not everybody is.

 

[stevendaryl]

This is getting off-topic. We've had this discussion before and we disagree deeply on this issue.

I was responding to your claim "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".

The outcome being determined by the current state of the universe is the part that I'm claiming is false.

 

[Mentz114]

I was responding to your claim "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".

The outcome being determined by the current state of the universe is the part that I'm claiming is false.

Fair enough. That is my central thesis. What else could possibly decide ?

 

[stevendaryl]

Fair enough. That is my central thesis. What else could possibly decide ?

I'm not saying that I know the answer, I'm saying that the answer does not come from standard QM by taking into account the environment.

 

[Mentz114]

I'm not saying that I know the answer, I'm saying that the answer does not come from standard QM by taking into account the environment.

That's a reasonable view. Any ire I have is directed at MWI.

However, I think classical statistical mechanics and standard QM together offers an explanation. I would heartily recommend a close reading of chapter 2, especially section 2.6 of "The Quantum Theory of Motion" by Peter Holland. I get a clear mental structure from this, and no mystery.

I'm sure this is also done in the 'Thermal interpretation' but Hollands discussion is easier ( for me anyway).

[edited the title of the book]

 

[stevendaryl]

I'm not saying that I know the answer, I'm saying that the answer does not come from standard QM by taking into account the environment.

I don't want to spend more time on this, except to say that it would seem to me that the assumption that facts about the rest of the universe determine the outcome of measurements would contradict Bell's inequality. Maybe there is a loophole, but there certainly is no consensus that there is such a loophole.

 

[Jilang]

I don't want to spend more time on this, except to say that it would seem to me that the assumption that facts about the rest of the universe determine the outcome of measurements would contradict Bell's inequality. Maybe there is a loophole, but there certainly is no consensus that there is such a loophole.

I am reminded to remind you that quite recently you showed how the Bells inequality is violated for probabilities but not the probability amplitudes. In QT Amplitudes add, probabilities don't. Hidden variables only become a problem when one considers the probabilities rather than the amplitudes. Now, what would that suggest? (I have no suggestions)

 

[stevendaryl]

I am reminded to remind you that quite recently you showed how the Bells inequality is violated for probabilities but not the probability amplitudes. In QT Amplitudes add, probabilities don't. Hidden variables only become a problem when one considers the probabilities rather than the amplitudes. Now, what would that suggest? (I have no suggestions)

Yes, that is an interesting observation, but I don't know what to make of it.

 

[Mentz114]

I don't want to spend more time on this, except to say that it would seem to me that the assumption that facts about the rest of the universe determine the outcome of measurements would contradict Bell's inequality. Maybe there is a loophole, but there certainly is no consensus that there is such a loophole.

(my emphasis)
Do you mean through non-locality ?
What makes photon detectors click is correlations between probability amplitudes that happen right at the detector. These correlations could have been present after preparation - or is that just another NLHV theory ?

[Stephen, do you have a ref to the post where you did the work referred to by jilanq?]

 

[Jilang]

It was here at #11
https://www.physicsforums.com/threa...nonlocal-hidden-variable.875064/#post-5496299

 

[nolxiii]

So basically, either MWI, which is clearly crazy, or alternatively the universe depends on quantum decision fairies?

This more or less sum it up?

 

[PeterDonis]

What, exactly, are you doubtful about? Are you still talking about the issue of whether very weird outcomes actually happen in MWI?

Yes. The particular claim in question in what you quoted was the claim that when someone rolls a die, there must be six MWI branches created, one for each possible result of the die roll. I don't see why that must be the case, because I don't see how any quantum superpositions play a role in determining how the die comes up. As far as I know, die rolling is a classical process; there is no quantum indeterminacy involved. It's not the same as a radioactive atom decay determining some result. And if there is no quantum indeterminacy involved, then there is no MWI branching. There is just a classical deterministic process, which only looks random to us because we have insufficient knowledge of the initial conditions to predict the outcome. My more general point is that the same might apply to lots of cases which are cavalierly assumed, in pop science writings on the MWI, to lead to MWI branching.

MWI says that every possibility which (like cat state) arises from quantum superposition, is realized.

Yes; the cat state in the Schrodinger's cat experiment is explicitly assumed to depend on a quantum superposition, the decay of a radioactive atom. But that is not the case for die rolls. See below.

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.

This "presumably" is precisely the presumption I am questioning. Variability in the past is not enough; we are not talking about the fact that over a large number of dice rolls, each number will come up, on average, 1 in 6 times. We are talking about a presumption that, for a single die roll, the outcome has some significant dependence on a quantum superposition, like it does in the cat experiment. That has to be the case for the MWI to apply at all; you agree with that in what I quoted above.

But a single die roll, as far as I can tell, does not depend on any quantum superposition. It depends on a variety of initial conditions that are, at least at our current level of technology, uncontrollable, but that's not the same as depending on a quantum superposition. There are no radioactive atoms inside dice whose decay affects the outcome. There is just, as I said above in response to stevendaryl, a classical process whose outcome is only unpredictable to us because we have insufficient knowledge of the initial conditions. If quantum indeterminacy were involved, even perfect knowledge of initial conditions would be insufficient to predict the outcome: but I am not aware that anyone actually thinks that is the case for die rolls. They just fail to realize they are implying that when they make claims about MWI branching.

 

[nikkkom]

> 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.

This "presumably" is precisely the presumption I am questioning. Variability in the past is not enough; we are not talking about the fact that over a large number of dice rolls, each number will come up, on average, 1 in 6 times. We are talking about a presumption that, for a single die roll, the outcome has some significant dependence on a quantum superposition, like it does in the cat experiment. That has to be the case for the MWI to apply at all; you agree with that in what I quoted above.

But a single die roll, as far as I can tell, does not depend on any quantum superposition.

It depends on the large set of prior events, some of them are clearly quantum. How strong the muscles of the thrower are, how precisely nerve impulses are translated into muscle action. Nerve impulses are electric. Human body experiences some 5000 radioactive decays per second from K40 and C14, and also cosmic radiation constantly showers us. Those are quantum processes, and they _directly_ add electric noise to nerve signals. Brownian motion of air molecular is quantum too. Muscle action is a chemical reaction in cells (some proteins change configuration), this is also affected by quantum effects.

 

[PeterDonis]

It depends on the large set of prior events, some of them are clearly quantum.

Sure, there are quantum events going on; but the question is whether the result of the die roll--which of the six sides comes up--depends on any of the superpositions in those events.

Let me try to reframe my point another way. In the Schrodinger's cat experiment, there are all sorts of quantum events going on inside the cat, but the key observable--whether the cat is dead or alive--does not, by hypothesis, depend on any of them. It depends only on whether or not a particular radioactive atom, outside the cat's body, decays within a certain period of time. The atom's state is in a superposition of decayed/not decayed, and the way the experiment is set up, the dynamics links that pair of atom states, decayed/not decayed, with the particular pair of cat states dead/alive. That is what makes MWI proponents say that the cat must end up in a superposition of dead/alive.

Compare this with a die roll. Sure, there are all sorts of quantum fluctuations going on in the die, in the thrower's hands and arms and nerves, in the surrounding air, etc. But none of them are linked to the result of the die roll--which side comes up--in the way the radioactive atom's state is linked to the cat's state above, just as in the above example, the cat's dead/alive state is not linked to any of the umpteen quantum superpositions inside its body, in the air molecules in the box, etc. Similarly, none of those umpteen quantum superpositions in the die and the thrower and the environment are linked, by the dynamics, to the die being in a superposition of coming up one/two/three/four/five/six. Or at least I would like to see some MWI proponent give me some reason to believe that there is some such link, other than "presuming" that this is the case. As far as I know, no MWI proponent has ever done that; they all just wave their hands and presume. That's what I'm objecting to.

 

[nikkkom]

Sure, there are quantum events going on; but the question is whether the result of the die roll--which of the six sides comes up--depends on any of the superpositions in those events.

Let me try to reframe my point another way. In the Schrodinger's cat experiment, there are all sorts of quantum events going on inside the cat, but the key observable--whether the cat is dead or alive--does not, by hypothesis, depend on any of them. It depends only on whether or not a particular radioactive atom, outside the cat's body, decays within a certain period of time. The atom's state is in a superposition of decayed/not decayed, and the way the experiment is set up, the dynamics links that pair of atom states, decayed/not decayed, with the particular pair of cat states dead/alive. That is what makes MWI proponents say that the cat must end up in a superposition of dead/alive.

Compare this with a die roll. Sure, there are all sorts of quantum fluctuations going on in the die, in the thrower's hands and arms and nerves, in the surrounding air, etc. But none of them are linked to the result of the die roll

Let's assume that the above is true.

There is another argument. MWI claims that not only this branch, with exactly this dice and this thrower exists before the throw. There are countless other branches, some of them very similar (so the dice throw is happening there too) but have slightly different dice, and/or slightly different thrower (stronger or weaker, or more excited than in other branch, so he throws the dice differently). In some of those branches, the result will be 6.

 

[PeterDonis]

MWI claims that not only this branch, with exactly this dice and this thrower exists before the throw. There are countless other branches, some of them very similar (so the dice throw is happening there too) but have slightly different dice, and/or slightly different thrower (stronger or weaker, or more excited than in other branch, so he throws the dice differently). In some of those branches, the result will be 6.

That just pushes the question back a step: how did these previously existing branches with slightly different initial conditions for the die and the thrower come into existence? Of course if branching events are ubiquitous it's easy to see how, but again, that's precisely the presumption that I am questioning. Schrodinger's Cat-type situations are not ubiquitous; it takes very careful experimental setups to create them.

In fact, the alternate argument you are giving here implicitly admits that branching events are not ubiquitous, because it implicitly admits that the die roll itself is not a branching event. There are branches in which the die comes up each way, but that's because there were already branches in which the die was set up to come up that way. The die roll itself causes no branching at all. But if we allow that the die roll doesn't cause branching, what justification is there for assuming that there are all these branches around to begin with?

 

[nikkkom]

That just pushes the question back a step: how did these previously existing branches with slightly different initial conditions for the die and the thrower come into existence?

By multiplying since the Big Bang.

For one, chemical processes are quantum. Which molecules clump into which dust grains in the proto-Solar system depends on molecules' states. There are enormous numbers of "Schrödinger's cat" situations in the protoplanetary cloud. Copenhagen says only one of the possible outcomes is realized; MWI says _all_ of them exist.

While most of them are vastly different from the branch we are in, some are only slightly different.

I think I'll stop repeating myself if you are still not getting it. I can't explain it any better.

 

[PeterDonis]

Which molecules clump into which dust grains in the proto-Solar system depends on molecules' states. There are enormous numbers of "Schrödinger's cat" situations in the protoplanetary cloud.

Hmm. So basically, the idea is that the emergence of classical initial conditions depends on quantum indeterminacy. That seems to lead to branching being somewhere in between the extreme MWI position I have been arguing against, and the position I have been arguing for (or at least stating as an objection). For example, rolling a die or flipping a coin would not cause branching; but somewhere in the far past there would have been branches created with different classical initial conditions that lead to different results for the die rolls or coin flips (or even different sets of die rolls or coin flips being made).

 

[akvadrako]

For example, rolling a die or flipping a coin would not cause branching;

Have you seen this paper?

Origin of probabilities and their application to the multiverse (2012)
https://arxiv.org/abs/1212.0953

They do some shallow analysis of a coin flip and billiards, concluding that quantum events almost completely determine the outcome.

 

[stevendaryl]

(my emphasis)
Do you mean through non-locality ?
What makes photon detectors click is correlations between probability amplitudes that happen right at the detector. These correlations could have been present after preparation - or is that just another NLHV theory ?

In the emphasized text, I thought I was paraphrasing your phrase:

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.

I thought you were saying that the outcome of a measurement is actually deterministic, depending on details of the current state of the universe. That would seem to be in violation of Bell's Inequality, unless
(1) the details affected the measurement outcomes through FTL means (nonlocality), or
(2) the details affected not only the measurement outcome, but also which measurement was made (superdeterminism).
(Those are the two loopholes to Bell's proof that I know of.)

I'm making an assumption here that the "current state of the universe" would count as a "hidden variable" in the sense of Bell.

[Stephen, do you have a ref to the post where you did the work referred to by jilanq?]

I don't remember the post, but my observation was that amplitudes for quantum mechanics work very much like probabilities for classical stochastic processes. I reconstructed my little essay about this here:
https://www.physicsforums.com/threads/amplitudes-probabilities-and-epr.895519/

 

[stevendaryl]

Yes. The particular claim in question in what you quoted was the claim that when someone rolls a die, there must be six MWI branches created, one for each possible result of the die roll. I don't see why that must be the case, because I don't see how any quantum superpositions play a role in determining how the die comes up.

Yes, this is an issue about ergodicity (or something like that). What I've assumed is that if a system has two possible states, |\psi_A\rangle and |\psi_B\rangle, and they have the same expectation value for the energy and other conserved quantities (such as momentum, angular momentum, charge, etc.), then there will typically be a nonzero transition probability to go from one state to the other. This amounts to an assumption that for sufficiently complex systems there are no "accidentally" conserved quantities (that is quantities that are conserved by hamiltonian evolution, but don't correspond to the usual conserved currents that come from symmetries of the Hamiltonian).

 

[stevendaryl]

Yes, this is an issue about ergodicity (or something like that). What I've assumed is that if a system has two possible states, |\psi_A\rangle and |\psi_B\rangle, and they have the same expectation value for the energy and other conserved quantities (such as momentum, angular momentum, charge, etc.), then there will typically be a nonzero transition probability to go from one state to the other. This amounts to an assumption that for sufficiently complex systems there are no "accidentally" conserved quantities (that is quantities that are conserved by hamiltonian evolution, but don't correspond to the usual conserved currents that come from symmetries of the Hamiltonian).

As an example, consider a marble inside a sealed glass jar. Classically, the marble is not going to get out of the jar without breaking the jar. Quantum mechanically, though, the particles making up the marble will have associated wave functions, and since the glass is not infinitely thick or infinitely dense, each wave function will not abruptly go to zero inside the glass. So I would expect that each particle has a nonzero chance of tunneling through the glass to escape. Raise that tiny probability to Avogadro's number, and you'll get a really, really, tiny (but nonzero) probability that the entire marble tunnels out. In Many-Worlds, the meaning of any nonzero probability of some event is that it is the measure of the set of "worlds" for which that event occurs.

 

[PeterDonis]

Have you seen this paper?

No, I hadn't. It looks interesting, I'll give it a detailed read.

 

[Daniel Valient]

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.

Well, I think the first example would be Murray Gell-Man's famous declaration (apparently appropriated from T.H.White) that "Everything not forbidden is compulsory." https://en.wikipedia.org/wiki/Totalitarian_principle
And then go back to that quote from Max Tegmark (taken from his official website http://space.mit.edu/home/tegmark/) "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".
Tegmark is saying that no matter what, no matter how nice or how ethical of a person you are...you are going to rob a bank in trillions of timelines (not just in one timeline but in trillions... because there trillions of different ways to rob a bank which all have to be represented in the multiverse)
And the reason I keep asking experts about this (and why I started this thread in the first place) is because I'm not a fan of this notion that every physically possible event has to take place. For various ethical and moral reasons, I'm hoping that it turns out to be false
But I've asked several experts about is and the answer is overwhelmingly on the side that mwi requires EVERYTHING to happen. When I asked David Deutsch about this he understood that i was trying to test the limitations of what was "physically possible". I asked him about the same "Bush marries Clinton" scenario with the understanding that this was the most absurd, ridiculous scenario that I could think of...And Deutsch still affirmed that in a very slim percentage of universes this scenario was not only likely to happen, but required to happen
I think that you are saying we are not held to this definition of determinism, because we are operating on a classical level and not on a quantum level...but I think that most scientists would object to this... they would say that we do not control the subatomic particles...the subatomic particles control us. If the subatomic particles are required to carry out every physically possible interaction, then we are just along for the ride...
But at the same time Frank Tipler (who, like Deutsch is one of my scientific heroes) seems to agree with you on some level...he seems to think that some absurd scenarios might not happen (even if they are physically possible). I interviewed him for a magazine I used to work for and while he is still stridently in favor of mwi (in fact at one point in this interview, he characterized scientists who oppose mwi as "idiots") he did say that the Bush / Clinton marriage might only be possible in our imagination.
I have hesitated to link to this interview because I don't quite understand why Tipler diverges from Deutch/ Tegmark et al on this. I cannot really extrapolate from his comments why he thinks that some physically possible events are exempt from taking place (probably my shortcomings as an interviewer). Other than that, he seems to have the same understanding of many-worlds that Deutsch, Tegmark and all the others have...so his views may be similar to yours in that sense.
I also hesitate to link to this because the beginning has vaguely philosophical content...to get to the stuff about "many worlds" (and some of his comments about mwi are actually pretty amazing) skip to the 2:50 mark...it goes from 2:50 to about 10:42 (and then more stuff about determinism around 20:40)

 

[Daniel Valient]

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

Which of those scientists support consistent histories?
IIRCC consistent histories is sort of like mwi except that the universe where the particle lands is somehow more real than the others ...so I feel it is somewhat similar to Bohm's theories (correct me if I'm wrong on this)
I do remember that essay on many worlds that Martin Gardner wrote where he lambasted mwi proponents and desperately tried to whitewash Stephen Hawking support for mwi...He claimed that Stephen Hawking believed in a kind of mwi where the parallel universes weren't actually real (which is demonstrably false...I know of at least one instance where hawking has gone on the record to say that the parallel universes are as real as the one we are currently experiencing).
So I think that Martin Gardner has muddied the waters on this issue and has tried to portray Hawking and others as being in the consistent histories camp because of his own personal bias...

 

[bhobba]

So basically, either MWI, which is clearly crazy, or alternatively the universe depends on quantum decision fairies?
This more or less sum it up?

No.

But actually study some QM before proceeding:
https://www.amazon.com/dp/0465062903/?tag=pfamazon01-20

Thanks
Bill

 

[bhobba]

Which of those scientists support consistent histories?

Gell Mann and Feynman after attending some lectures on it by Gell Mann

IIRCC consistent histories is sort of like mwi except that the universe where the particle lands is somehow more real than the others ...so I feel it is somewhat similar to Bohm's theories (correct me if I'm wrong on this)

Sort of, DH is the stochastic theory of histories but only one history actually occurs - in MW they all occur simultaneously.

I do remember that essay on many worlds that Martin Gardner wrote where he lambasted mwi proponents and desperately tried to whitewash Stephen Hawking support for mwi...He claimed that Stephen Hawking believed in a kind of mwi where the parallel universes weren't actually real (which is demonstrably false...I know of at least one instance where hawking has gone on the record to say that the parallel universes are as real as the one we are currently experiencing).
So I think that Martin Gardner has muddied the waters on this issue and has tried to portray Hawking and others as being in the consistent histories camp because of his own personal bias...

Really nothing can be gained by analysing why some choose one interpretation over another - its not off topic here but the mods, correctly, keep a tight reign on it because basically its philosophy.

Thanks
Bill

 

[bhobba]

And the reason I keep asking experts about this (and why I started this thread in the first place) is because I'm not a fan of this notion that every physically possible event has to take place. For various ethical and moral reasons, I'm hoping that it turns out to be false

Then don't ascribe to it. Many don't - I don't. But it was deliberately cooked up to be equivalent to the standard QM formalism so its unlikely to be disproved. When worked through such as by David Wallace is very beautiful mathematically:
https://www.amazon.com/dp/0198707541/?tag=pfamazon01-20

The answer to your question is MW deterministic or not depends on what you mean by deterministic. If you believe a theory needs to detail every question that can be asked such as what outcome will occur then its not deterministic - but if you think that's not a question to worry about then it is deterministic - probabilities enter into it via decision theory as what are the betting odds of a random world where such and such occurs. For what its worth I believe its entirely deterministic - but that's just me - it means diddly squat.

Thanks
Bill

 

[zonde]

And the reason I keep asking experts about this (and why I started this thread in the first place) is because I'm not a fan of this notion that every physically possible event has to take place.

I think it might be worth separating two different meanings for statement that "everything physically possible happens in multiverse".
(1) In whole multiverse taken all the branches since dawn of time everything physically possible happens.
(2) Since particular point in time in particular branch everything physically possible happens.
I think it's easy to see that "everything physically possible" is much broader in first statement than in second. And if we speak about trowing a dice in the sense of second statement, physically possible outcomes would be determined by physics laws. While if we speak about trowing a dice in the sense of first statement (picking subset of branches from the whole multiverse with similar situations) it's much more like classical probability and has very little to do with laws of physics.

I think it would be useful to check that argument "everything physically possible happens in whole multiverse" is not proposed as justification for what happens in particular branch after particular point in time. This seems related to PeterDonis arguments against taking too broad meaning for "everything physically possible".

 

[zonde]

As an example, consider a marble inside a sealed glass jar. Classically, the marble is not going to get out of the jar without breaking the jar. Quantum mechanically, though, the particles making up the marble will have associated wave functions, and since the glass is not infinitely thick or infinitely dense, each wave function will not abruptly go to zero inside the glass. So I would expect that each particle has a nonzero chance of tunneling through the glass to escape. Raise that tiny probability to Avogadro's number, and you'll get a really, really, tiny (but nonzero) probability that the entire marble tunnels out. In Many-Worlds, the meaning of any nonzero probability of some event is that it is the measure of the set of "worlds" for which that event occurs.

Ar you sure that in quantum mechanics you can simply multiply probabilities of each particle tunneling through the glass to get combined probability of whole marble tunneling trough the glass?

 

[stevendaryl]

I think it might be worth separating two different meanings for statement that "everything physically possible happens in multiverse".
(1) In whole multiverse taken all the branches since dawn of time everything physically possible happens.
(2) Since particular point in time in particular branch everything physically possible happens.
I think it's easy to see that "everything physically possible" is much broader in first statement than in second. And if we speak about trowing a dice in the sense of second statement, physically possible outcomes would be determined by physics laws. While if we speak about trowing a dice in the sense of first statement (picking subset of branches from the whole multiverse with similar situations) it's much more like classical probability and has very little to do with laws of physics.

I think it would be useful to check that argument "everything physically possible happens in whole multiverse" is not proposed as justification for what happens in particular branch after particular point in time. This seems related to PeterDonis arguments against taking too broad meaning for "everything physically possible".

Even though this issue is phrased as a question about MWI, there is a core question that presumably is a matter of pure quantum mechanics.

When I perform an action such as rolling a pair of dice, there are two different sources of uncertainty about the result:

1. There is classical uncertainty, due to lack of precise information about the initial state of my body, the dice, the air currents affecting the dice while they are dropping, the irregularity of the surface they are dropped on, etc. (Actually, besides not knowing these details, there is also the matter that it is computationally impossible to take them all into account, anyway.)
2. There is quantum uncertainty, due to the nonexistence of precise values for positions and momenta of the particles making up the dice, my body, etc.

For most classically random processes, such as rolling a dice or flipping a coin, effect #1 completely swamps out effect #2, so you can say that quantum mechanics has no role in the outcome. The technical issue, which is independent of whether we're talking about MW or not, is: What is the range of possibilities due exclusively to effect #2? Would quantum uncertain by itself produce nonzero probabilities for all 6 outcomes for a die roll? My feeling is that yes, all 6 possibilities (plus even weirder outcomes) for the roll of a die would have a nonzero probability. But that's a technical question, and presumably it has a technical answer.

The second question is whether nonzero probability for an event implies for MWI that it happens in some "possible world". I thought that that is true as a matter of definition---the quantum probabilities for events are interpreted as measures on possible worlds.

 

[stevendaryl]

Ar you sure that in quantum mechanics you can simply multiply probabilities of each particle tunneling through the glass to get combined probability of whole marble tunneling trough the glass?

No, you certainly cannot do that. I was speaking loosely. The probabilities will be correlated, so you can't just treat them as independent. I was just sketching a first cut at figuring out a probability for the entire marble tunneling out, sort of along the lines of freshman physics problems that say "Ignoring friction..."

But my point is that there is no good reason (that I know of) to believe that the quantum probability for weird events (such as a marble tunneling outside of a closed glass jar) is strictly zero. For practical purposes, people treat sufficiently low probabilities as if they were zero, and by that standard, we can say that certain things are impossible. But from the point of view of MWI, which is the topic here, I think that any nonzero probability means that something is possible.

 

[secur]

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.

Well, I think the first example would be Murray Gell-Man's famous declaration (apparently appropriated from T.H.White) that "Everything not forbidden is compulsory." https://en.wikipedia.org/wiki/Totalitarian_principle

And then go back to that quote from Max Tegmark (taken from his official website http://space.mit.edu/home/tegmark/) "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 ...".

But at the same time Frank Tipler ... at one point in this interview, he characterized scientists who oppose mwi as "idiots".

Every one of these examples is pop science, so you haven't addressed @PeterDonis's request. Since these statements aren't justified by the actual physics, these people undoubtedly qualify them, in published papers, with some form of "maybe".

Do you understand the difference between "pop-sci" vs. "peer-reviewed"? This is a vital point. It's the difference between chatting with your pals at the pub, and testifying in court.

MWI does in fact say that "everything possible" (what that means is subject to debate, of course) must happen in some universe. But MWI is far from proven. Crucially, they haven't been able to derive Born rule. Haven't even attempted to address issues involved with consciousness. For instance Tegmark's concept "your twin" is thoroughly vague. MWI is a philosophical stance and will always remain so (probably). Personally, I neither believe nor disbelieve MWI. Neither attitude is logical, given the facts of QM.

To get an idea of the veracity of these statements, note Tipler's "scientists who oppose MWI are idiots". Think about it. Is it true? No. It demonstrates that you can't trust these casual pop-sci statements, which are purposely controversial. Taking pop-sci seriously is on a par with taking politicians seriously.

 

[PeterDonis]

the first example

Is not a textbook or peer-reviewed paper.

that quote from Max Tegmark

Is not a textbook or peer-reviewed paper.

i've asked several experts

Still not a textbook or peer-reviewed paper.

I interviewed him for a magazine

Still not a... you get the idea.

Scientists say lots of things on their websites, in pop science articles, in TV shows, etc., and even in informal conversations with others, that they know they can't get away with in actual textbooks or peer-reviewed papers. That's why PF has rules about acceptable sources.

 

[Daniel Valient]

Is not a textbook or peer-reviewed paper.
Is not a textbook or peer-reviewed paper.
Still not a textbook or peer-reviewed paper.
Still not a... you get the idea.

Scientists say lots of things on their websites, in pop science articles, in TV shows, etc., and even in informal conversations with others, that they know they can't get away with in actual textbooks or peer-reviewed papers. That's why PF has rules about acceptable sources.

I think I disagree with the notion that professional scientists can only communicate with us via textbooks or peer reviewed papers. One of the jobs of a professional scientist is to extrapolate information and present it in a way that is accessible to the masses...

But at any rate, here is a paper written by Bryce Seligman DeWitt from Physics Today (the flagship publication of the American Institute of Physics which is peer reviewed)
https://scholar.google.com/scholar_lookup?author=B. S.. DeWitt&journal=Physics Today&volume=23&pages=9&publication_year=1970

In the paper DeWitt says "Actually, Everett/ Wheeler/ Graham do not in the end exclude any clement of the superposition. All the worlds are there, even those in which everything goes wrong and all the statistical laws break down."

Here's another paper I just happened to be reading that reiterates mwi's demand for every physically possible outcome to be represented... https://arxiv.org/pdf/0903.2211.pdf

As Dewitt notes, Hugh Everett himself believed in the absurd, statistically unlikely timelines. Before Tegmark ever popularized the idea of quantum suicide, Hugh Everett was reportedly telling friends and family members that many worlds guaranteed human immortality (a fact which is even referenced in his daughter's suicide note...)

I mean I could probably find a million references to "every physically possible outcome" in academic papers/ textbooks on mwi...But I think there is confusion between you and I as to what "every physically possible outcome" actually means (Lord knows I'm confused... which is exactly why I've tried to clarify it with scientists/ researchers who I respect)

But I don't understand why you think that scientists like Deutsch, Tegmark et al. would intentionally mislead people on this issue. It just seems to me that they are taking mwi's "every physically possible scenario" requirement at face value. I don't see them as trying to cash in or raise their pop science profile. In fact I feel that many of them are reticent when it comes to discussing the absurd and/or disturbing implications of mwi.

 

[secur]

@Daniel Valient, I agree, even assert, that MWI requires "all possible outcomes" to be realized. What that means needs unpacking. Do all 6 results from rolling a die occur in different branches? Or is that not a quantum, but purely classical, phenomenon? Do the laws of (quantum) physics allow some variation of "you" (however that's defined) to have a completely different personality? Such questions have some interest entirely apart from MWI. Unfortunately the state of our current knowledge, especially concerning personalities and their hypothetical relation to quantum phenomena, is so inadequate at this time, that it doesn't seem worth discussing in any depth.

MWI is just a postulate, one of many interpretations. As Wikipedia correctly says:

MWI is ... currently considered a mainstream interpretation along with the other decoherence interpretations, collapse theories (including the historical Copenhagen interpretation), and hidden variable theories such as the Bohmian mechanics.

It has various problems. Perhaps the biggest is reproducing the Born rule. Note that there are competing detailed MWI versions, and although most claim to be "right", there's no real consensus. All advocates admit - especially in published peer-reviewed journals - that it will be a long time, if ever, that MWI (any version) makes a new prediction which can be experimentally verified.

You seem to be asking, "let's suppose, contrary to current understanding, that MWI really is true. If so, exactly what branches might be possible?" That's too speculative for me, but I wish you luck with it.

But I don't understand why you think that scientists like Deutsch, Tegmark et al. would intentionally mislead people on this issue. ... I don't see them as trying to cash in or raise their pop science profile. ...

No doubt, some of them sincerely believe their favorite version. I'd hate to think they all do.

 

[Daniel Valient]

Every one of these examples is pop science, so you haven't addressed @PeterDonis's request. Since these statements aren't justified by the actual physics, these people undoubtedly qualify them, in published papers, with some form of "maybe".

Do you understand the difference between "pop-sci" vs. "peer-reviewed"? This is a vital point. It's the difference between chatting with your pals at the pub, and testifying in court.

MWI does in fact say that "everything possible" (what that means is subject to debate, of course) must happen in some universe. But MWI is far from proven. Crucially, they haven't been able to derive Born rule. Haven't even attempted to address issues involved with consciousness.

I agree with this... mwi doesn't solve the initial problem of why measurement/ consciousness seems to trigger the collapse (or in the case of mwi, the universal split)

Every one of these examples is pop science, so you haven't addressed @ For instance Tegmark's concept "your twin" is thoroughly vague. MWI is a philosophical stance and will always remain so (probably). Personally, I neither believe nor disbelieve MWI. Neither attitude is logical, given the facts of QM.

To get an idea of the veracity of these statements, note Tipler's "scientists who oppose MWI are idiots". Think about it. Is it true? No.

Tipler is one of my heroes but I do disagree with him on this. There are some very bright scientists (Roger Penrose and many others) who vehemently oppose mwi. In fact I probably oppose mwi. None of the interpretations really make sense, but if I had to choose between mwi and Copenhagen I'd probably go with Copenhagen...

 

[PeterDonis]

I think I disagree with the notion that professional scientists can only communicate with us via textbooks or peer reviewed papers.

I suppose it is possible in principle for a scientist to adhere to the same standards of rigor in informal communications like pop science articles or TV specials as he does in formal communications like textbooks or peer reviewed papers. But in practice it rarely if ever happens.

I don't understand why you think that scientists like Deutsch, Tegmark et al. would intentionally mislead people on this issue.

I haven't said they are intentionally misleading people. I'm just saying it's hard to keep a sharp distinction between the basic physics--what is necessarily implied by our best current experimental knowledge--and interpretations that go beyond that. In formal communications, there are at least other experts who can help to enforce that distinction (though that doesn't always happen). But if the audience is lay people, there is nobody to do that.

 

[atyy]

Well, I think the first example would be Murray Gell-Man's famous declaration (apparently appropriated from T.H.White) that "Everything not forbidden is compulsory." https://en.wikipedia.org/wiki/Totalitarian_principle

The totalitarian principle is not about MWI - it is an uncontroversial statement about renormalization in quantum field theory.

 

[bhobba]

I suppose it is possible in principle for a scientist to adhere to the same standards of rigor in informal communications like pop science articles or TV specials as he does in formal communications like textbooks or peer reviewed papers. But in practice it rarely if ever happens.

It happens all the time. I was a programmer for 30 years - 20 at the team leader level and I attended many meetings with users who knew nothing about the technicalities - nor should they. They wanted to know what we could do for them. I was very 'loose' with all sorts of stuff.

Same here - when scientists speak informally they are often, like I was, a bit loose. The reason I know Gell-Mann adhered to DH is he wrote papers on it. The reason I know Feynman was converted to it is Gell-Mann described how he discussed it with him and attended his lectures o it. This is the type of evidence you want.

Thanks
Bill

 

[mfb]

I agree with this... mwi doesn't solve the initial problem of why measurement/ consciousness seems to trigger the collapse (or in the case of mwi, the universal split)

There is no "trigger" necessary because the process is continuous in MWI, but decoherence shows why those worlds split.

 

[PeterDonis]

when scientists speak informally they are often, like I was, a bit loose.

In other words, they don't adhere to the same standards of rigor as they do in formal communications. Which is what I said.

Your analogy with a programmer explaining things to a user isn't valid IMO, because the user is not trying to learn programming; they're just trying to get work done. So an informal, "loose" explanation is good enough. People who ask questions here on PF are trying to learn the actual science--at least, that's the assumption that underlies the PF rules on acceptable sources (and if we find out people aren't really trying to learn the actual science, we cut the discussion short if possible). An informal, "loose" explanation isn't enough for that.

 

[PeterDonis]

This is the type of evidence you want.

If I'm interested in who favors what interpretation, yes. But not if I'm interested in what a given interpretation actually entails.

 

[nikkkom]

mwi doesn't solve the initial problem of why measurement/ consciousness seems to trigger the collapse (or in the case of mwi, the universal split)

It does solve it.

The thing it, MWI in fact does not precisely say that there are "splits". There are no splits at all. In Schrödinger's cat situation, unobserved "cat in a box" system exists in a superposition (even in Copenhagen) - it does not split into gazillions of branches, it is still one system.

What MWI says is that a similar superposition situation arises when you observe the box. The "you + opened box" system does not split into gazillion branches - instead, now this system is in superposition of "you see a dead cat" and "you see a live cat". It is still one system. (If you disagree, then you must be agreeing that Copenhagen interpretation of the "unobserved box" system also includes world splits).

No collapse happened when box was observed. Thus, no concept of measurement needs explaining. In MWI, measurement is merely "interaction which entangles observer with the observed subsystem".

You can think about "gazillion of branches" method of describing it as a way to explain superposition to laymen.

 

[secur]

Well, I think the first example would be Murray Gell-Mann's famous declaration (apparently appropriated from T.H.White) that "Everything not forbidden is compulsory." https://en.wikipedia.org/wiki/Totalitarian_principle

The totalitarian principle is not about MWI - it is an uncontroversial statement about renormalization in quantum field theory.

That principle applies throughout QM (/QFT), including renormalization and MWI. Murray Gell-Mann originally thought of it in relation to particle decay but its relevance to MWI is direct and important. It's precisely the main point of this thread (one of them anyway): that "every possible possibility" must be realized in a branch, or universe, of the many worlds wavefunction.

Gell-Mann "appropriated" the phrase from White but White knew nothing about QM, talking about an unrelated topic (dictatorial government). The principle is inherent in QM and was known from the beginning, but Gell-Mann was the first to single it out (AFAIK) and emphasize its importance and applications. IMHO he deserves the entire credit for it.

It does solve it.

Such a statement should never be made in reference to MWI. It really doesn't matter what is supposed to be "solved" but it's especially true if it has anything to do with measurement, collapse, observers, and consciousness, as in the present case.

All these statements are acceptable: "It may possibly solve it"; "according to some advocates it does solve it"; "it offers a solution which of course is not proven, well-defined, or entirely accepted by the physics community"; "IMHO it solves it, but of course many physicists would disagree". And similar variations.

If we all understood and agreed to the above, then the simple, direct "it does solve it" would be acceptable as shorthand. But since we don't all understand and agree it seems necessary to flag this statement as a mistake.

 

[nikkkom]

MWI does not have and does not need a concept of "measurement" as something special and distinct from all other interactions in quantum systems.
MWI does not postulate any "collapse" to be happening.
Thus, it does not have "problem of why measurement/ consciousness seems to trigger the collapse".

I don't see what are you arguing against.

 

[secur]

I shouldn't have referred to your post, @nikkkom. I had been glancing through "The Beginning of Infinity" by David Deutsch and accidentally vented my annoyance on your statement, for which I apologize. My comments are actually meant for DD and others of that ilk. This book is NOT bad science; it's not even bad pop-science: it's bad science fiction.

 

[n01]

I have three small questions that I figure can be answered here instead of cluttering the forum with them.

Under MWI, how is it that this reality (the sum total of logical relations between objects in the universe interacting with each other) is apparent (or real) as opposed to being none other than what it is itself?

Is Occam's Razor superseded or discredited by Everettian QM in explaining an infinitude of events?

And finally, can the Church-Turing-Deutsch principle ever hope to amount to anything more than a theory? Can it be proved?

 

[bhobba]

Under MWI, how is it that this reality (the sum total of logical relations between objects in the universe interacting with each other) is apparent (or real) as opposed to being none other than what it is itself?

Its easy.

Due to interactions you end up with what's called a mixed state that is written as ∑pi |bi><bi| - the |bi> are the outcomes of the observation, interaction etc etc. This is from the formalism of QM - every interpretation has it. Now in MW the |bi><bi| are interpreted as separate worlds and everything just keeps evolving - no single outcome is singled out - they all just occur. Using decision theory you can show the pi are the probability that if you randomly pick a world what is the probability it will be |bi><bi|. Its really is that simp;le. Of course the details are technical and mathematical and can be found here:
https://www.amazon.com/dp/0198707541/?tag=pfamazon01-20

I don't know enough about the Church-Turing-Deutsch principle to know the current state of ply - but predicting future progress is a mugs game so who knows.

Thanks
Bill