Sidney Coleman's opinion on interpretation in his Dirac lecture

[gentzen]

pines-demon quoted from Sidney Coleman's Dirac Lecture "Quantum Mechanics in Your Face" (https://arxiv.org/abs/2011.12671)

The other day I was looking at a British videotape of Feynman explaining elementary concepts in science to an interrogator, whom I think was the producer Christopher Sykes. He asked Feynman to explain the force between
magnets. Feynman hemmed and hawed for a while, and then he got on the right track, and he said something that’s dead on the nail. He said:

You’ve got it all backwards, because you’re not asking me to explain the force between your pants and the seat of your chair. You want me, when you say the force between magnets, to explain the force between magnets in terms of the kinds of forces you think of as being fundamental—those between bodies in contact.

Obviously, I’m not phrasing it as wonderfully as Feynman. But, well, as Picasso said in other circumstances, it doesn’t have to be a masterpiece for you to get the idea. We physicists all know it’s the other way around: the fundamental force between atoms is the electromagnetic force which does fall off as one over R squared. Christopher Sykes was confused because he was asking something impossible. He should have asked to explain the pants-chair force in terms of the force between magnets. Instead he asked to derive the fundamental quantity in terms of the derived one.

Likewise, a similar error is being made here. The problem is not the interpretation of quantum mechanics. That’s getting things just backwards. The problem is the interpretation of classical mechanics.

and martinbn added "the full quote" of what Sidney Coleman said before (and refers to here) to make things clearer:

“Every successful physical theory swallows its predecessor alive.” But it does so by interpreting the concepts of the old theory in terms of the new, NOT the other way around. Thus our aim is NOT “the interpretation of quantum mechanics.” It is the interpretation of classical mechanics.

Sidney Coleman's opinion on interpretation in these two quotes is:

• Thus our aim is NOT “the interpretation of quantum mechanics.” It is the interpretation of classical mechanics.
• The problem is not the interpretation of quantum mechanics. That’s getting things just backwards. The problem is the interpretation of classical mechanics.

However, more quotes are needed to capture Coleman's position in his Dirac lecture:

I want to stress that I have made no original contributions to this subject. There is nothing I will say in this lecture, with the exception of the carefully prepared spontaneous jokes—that was one of them—that cannot be found in the literature.

The position I am going to advocate is associated with Hugh Everett in a classic paper.

I will argue the there is

NO special measurement process​

NO reduction of the wave function​

NO indeterminancy​

NOTHING probabilistic​

in quantum mechanics.

ONLY deterministic evolution​

according to Schrödinger’s Equation​

Zurek has made major contributions to the theory of decoherence—where instead of just saying it’s ridiculous or absurd, he actually raised a question one can talk about. He said: “If this is so, why do I the observer perceive only one of the outcomes?” This is now the question I will attempt to address: Zurek’s question. If there is no reduction of the wave packet, why do I feel at the end of the day that I have observed a definite outcome, that the electron is spinning up or the electron is spinning down?
In order to ease into this, I’d like to begin with an analysis of Neville Mott.

In Tom Stoppard’s play Jumpers, there’s an anecdote about the philosopher Ludwig Wittgenstein.

Now people say the reduction of the wave packet occurs because it looks like the reduction of the wave packet occurs, and that is indeed true. What I’m asking you in the second main part of this lecture is to consider seriously what it would look like if it were the other way around—if all that ever happened was causal evolution according to quantum mechanics. What I have tried to convince you is that what it looks like is ordinary everyday life.

Sidney Coleman's position in these quotes is:

• I have made no original contributions to this subject.
• Zurek ... actually raised a question one can talk about.
• In order to ease into this, I’d like to begin with an analysis of Neville Mott.
• Now people say the reduction of the wave packet occurs because it looks like the reduction of the wave packet occurs, and that is indeed true.

The connection to the annecdote about Wittgenstein definitively was an original contribution. This raises the question whether it was the only original contribution. Another likely original contribution is his ambiguous reframing: "The problem is the interpretation of classical mechanics."

But I don't think Sidney Coleman was intentionally lying when he denied having made original contributions. The scientists mentioned in the quotes above are Neville Mott, Hugh Everett and Wojciech Żurek. (Other scientists are mentioned in: "Some of the things I’ll say about probability later come from a paper by Jim Hartle, and one by Cambridge’s own Eddie Farhi, Jeffrey Goldstone, and Sam Gutmann.") So I wonder whether his position can be justified as a non-original selection from published works of Mott, Everett and Żurek, or whether it must be considered as an original position, which was never peer-reviewed or even worked-out properly.

 

[Demystifier]

I don't know whether Coleman's position contains something original, but there is something else that I find problematic. Coleman first says that his aim is not the interpretation of QM, but then he says that he will advocate the Everett's position. Well, the Everett's position is an interpretation of QM. Moreover, it is very questionable how successful this interpretation is. It is certainly not the mainstream interpretation that most physicists use in practice, so it cannot be said that it is very successful in a practical sense. So, when he says

“Every successful physical theory swallows its predecessor alive.” But it does so by interpreting the concepts of the old theory in terms of the new, NOT the other way around. Thus our aim is NOT “the interpretation of quantum mechanics.” It is the interpretation of classical mechanics. (my bolding)

it is very questionable whether this can be applied to the Everett's view of QM.

What I'm really saying is this. I agree that every successful physical theory should interpret the concepts of the old theory in terms of the new, not the other way around. However, QM in general, and Everett's QM in particular, is still not successful enough. QM still contains open conceptual questions within itself, that's why we have various interpretations, each with some advantages and drawbacks. Hence QM is still not understood sufficiently well to present, with full confidence, the interpretation of classical mechanics in terms of quantum mechanics.

 

[haushofer]

It's comparable to the time where the geocentric and heliocentric models both successfully explained planetary orbits. It was only in accepting the heliocentric model that modern cosmology could develop. From this modern standpoint the heliocentric model of course is to be preferred.

Sometimes I get the feeling physicists think that this whole interpretational issue is just a luxury which won't bring us any further in the development op physics. I think that's a huge mistake, comparable to how the catholic church in Galilei's time thought you could just see the heliocentric model possibly as some useful tool without any ontological or scientific consequences.

 

[Demystifier]

It's comparable to the time where the geocentric and heliocentric models both successfully explained planetary orbits. It was only in accepting the heliocentric model that modern cosmology could develop. From this modern standpoint the heliocentric model of course is to be preferred.

Sometimes I get the feeling physicists think that this whole interpretational issue is just a luxury which won't bring us any further in the development op physics. I think that's a huge mistake, comparable to how the catholic church in Galilei's time thought you could just see the heliocentric model possibly as some useful tool without any ontological or scientific consequences.

If the geocentric model preferred by the catholic church is the metaphor for the orthodox interpretation of QM, then the heliocentric model is the metaphor for which interpretation of QM?

I would say it must be some realist interpretation, which does not put an observer into the "center of the universe". So the main candidates seem to be the many worlds interpretation, the Bohmian interpretation, the consistent histories interpretation, and the objective collapse interpretation. But I would rule out many worlds, because it is the most extreme example of mistaking the map for the territory. Next I would rule out the objective collapse interpretation, not because it is wrong, but because it is an alternative theory, so it is not really an analog of the heliocentric model. Finally, the consistent history interpretation holds that reality depends on the framework, which is analogous to a statement that any object can be taken as the origin of coordinates, not to a statement that it must be the Sun. So I conclude that the best analog of the heliocentric model is the Bohmian interpretation. (Which, of course, does not make it right.)

 

[gentzen]

Coleman first says that his aim is not the interpretation of QM, but then he says that he will advocate the Everett's position. Well, the Everett's position is an interpretation of QM.

Careful, he only said "associated with Hugh Everett". Since Coleman is very careful with words, this means that he is not claiming to advocate for Everett's position.
And as John McAndrew remarked, Coleman gets asked if he is a follower of Everett’s Many Worlds interpretation at 1:04:20, and clarifies even more explicitly why he is very careful:

Yeah, but that's a tricky thing to say. That's like saying you're a Christian. I mean Everett wrote this one truly wonderful paper and then everyone got on their horse and rode off in all directions. The position I'm advocating is a position that (at least in my case) was certainly largely inspired by Everett's paper. Whether it's really Everett's position or not I would prefer not to discuss.

Peter Woit nicely captured the association between Coleman and Everett (in the comment above John McAndrew's):

Coleman explicitly does refer to Everett, and yes, he’s an Everettian in the sense of seeing no reason QM without a reduction postulate can’t describe the world as we know it. My point was just that he doesn’t invoke a splitting into “many worlds” to replace wave-function reduction.

 

[Sambuco]

I would say it must be some realist interpretation, which does not put an observer into the "center of the universe". So the main candidates seem to be the many worlds interpretation, the Bohmian interpretation, the consistent histories interpretation, and the objective collapse interpretation. But I would rule out many worlds, because it is the most extreme example of mistaking the map for the territory. Next I would rule out the objective collapse interpretation, not because it is wrong, but because it is an alternative theory, so it is not really an analog of the heliocentric model. Finally, the consistent history interpretation holds that reality depends on the framework, which is analogous to a statement that any object can be taken as the origin of coordinates, not to a statement that it must be the Sun. So I conclude that the best analog of the heliocentric model is the Bohmian interpretation. (Which, of course, does not make it right.)

I tend to agree with you regarding the comparison between Bohmian mechanics, many-worlds, and objective collapse. However, I think this is too narrow a view of realism, which traditionally associated "realism" with a $\psi$-ontic stance. Likewise, the concept of realism is also associated with the EPR-like idea that system variables must have a value for each instant of time. However, in the last 30-40 years, interpretations have been proposed that are $\psi$-epistemic but realist, in the sense of postulating a clear ontology. Personally, I see relational quantum mechanics positively.

Lucas.

 

[Demystifier]

However, in the last 30-40 years, interpretations have been proposed that are ψ-epistemic but realist, in the sense of postulating a clear ontology. Personally, I see relational quantum mechanics positively.

Are you saying that relational QM has a clear ontology? If you do, what is it?

 

[martinbn]

Are you saying that relational QM has a clear ontology? If you do, what is it?

That the particles, fields, atoms, molecules and so on, exist and interact with each other.

By the way I think that the analogy with the geocentric/heoliocentric sytems works better the other way around. Bohmian mechanics is analogous to the geocentric model. Because the geocentric model has all the epicycles and is more complicated to do calculations with, just like BM where you have all the additional equations for all the position variables. Also in the geocentric model the complicated trajectories of the planets are ment to be absolute, they are the true motions. Same in BM, the partical trajectories are taken seriously and are suposed to exist.

Of course both models are wrong from a modern point of view, beause each of them claims an absolute point of view. While we know now that they are two discription of the solar system from two different reference frames. To extend your analogy this says that the mordern view of the solar systems corresponds to the relational QM.

 

[Demystifier]

That the particles, fields, atoms, molecules and so on, exist and interact with each other.

I don't think that that's what the relational interpretation says. The crucial issue is the interpretation of entanglement, because particles can be entangled even when they do not interact. The relational interpretation says that entangled particles exist relative to each other. I don't see how relative existence provides a clear ontology.

Also a comparison with the relativity theory is useful. When Einstein proposed that space and time are relative to an observer, that was not a clear ontology. A clear ontology was proposed by Minkowski, who proposed that there is a 4-dimensional spacetime, which is absolute, not relative to something or someone.

Perhaps the best analog of the spacetime interpretation of relativity is the many world interpretation of QM. Just like the spacetime interpretation says that the real thing is all of space and time together as one entity, the many world interpretations says that the real thing is all of wave function for all particles together as one entity. But as I said, the many world interpretation is the most extreme mistake of map for the territory. Analogously, I think the spacetime interpretation of relativity is also a mistake of map for the territory, although not that extreme.

 

[martinbn]

I don't think that that's what the relational interpretation says. The crucial issue is the interpretation of entanglement, because particles can be entangled even when they do not interact. The relational interpretation says that entangled particles exist relative to each other. I don't see how relative existence provides a clear ontology.

But, it doesn't say that. It says that the state of a system is relative to another systems, not that a system exists relative to another.

Also a comparison with the relativity theory is useful. When Einstein proposed that space and time are relative to an observer, that was not a clear ontology. A clear ontology was proposed by Minkowski, who proposed that there is a 4-dimensional spacetime, which is absolute, not relative to something or someone.

I don't think this is a question of ontology. This is about clarifying the structure of space-time.

Perhaps the best analog of the spacetime interpretation of relativity is the many world interpretation of QM. Just like the spacetime interpretation says that the real thing is all of space and time together as one entity, the many world interpretations says that the real thing is all of wave function for all particles together as one entity. But as I said, the many world interpretation is the most extreme mistake of map for the territory. Analogously, I think the spacetime interpretation of relativity is also a mistake of map for the territory, although not that extreme.

There is no such thing as space-time interpretation of relativity!

ps By the way in the paper Coleman gives an argument of why there are definite single outcomes of a quantum measurment, which is very convincing. But you have in the past said many times that this is a prolem for QM that needs an interpretation. What do you think about Coleman's argument?

 

[gentzen]

ps By the way in the paper Coleman gives an argument of why there are definite single outcomes of a quantum measurment, which is very convincing.

Do you think that this argument is an original contribution by Coleman? Or is this argument artibutable to one of the given references, i.e. Mott, Everett, Zurek, or Hartle (or one of the other scientists he mentioned)?

 

[martinbn]

Do you think that this argument is an original contribution by Coleman? Or is this argument artibutable to one of the given references, i.e. Mott, Everett, Zurek, or Hartle (or one of the other scientists he mentioned)?

I think he attributes it to the others. I said Coleman's in the sense that it is from his paper, not that he was the first to present it.

 

[Demystifier]

It says that the state of a system is relative to another systems, not that a system exists relative to another.

Is there such a thing as a state of existence? If not, then there is no clear ontology.

There is no such thing as space-time interpretation of relativity!

I meant the block universe interpretation.

ps By the way in the paper Coleman gives an argument of why there are definite single outcomes of a quantum measurment, which is very convincing. But you have in the past said many times that this is a prolem for QM that needs an interpretation. What do you think about Coleman's argument?

I'm not sure that I understood his argument, but if this is just the Everett/many-world argument, then yes, this explains the definite single outcomes, but that's an interpretation. More specifically, for the outcome to be real (ontological) according to this explanation, the wave function itself should regarded as real (ontological), which is an interpretation.

 

[martinbn]

Is there such a thing as a state of existence? If not, then there is no clear ontology.

What do you call "a state of existence"? Is that related to the state of the state of the system?

I meant the block universe interpretation.

But that is not Minkowski's contribution to relativity, is it?

I'm not sure that I understood his argument, but if this is just the Everett/many-world argument, then yes, this explains the definite single outcomes, but that's an interpretation. More specifically, for the outcome to be real (ontological) according to this explanation, the wave function itself should regarded as real (ontological), which is an interpretation.

No, it is interpretation independent. It is older than the MWI.

 

[Demystifier]

What do you call "a state of existence"? Is that related to the state of the state of the system?

No, I mean the Bell's $\lambda$.

But that is not Minkowski's contribution to relativity, is it?

I think it is implicitly, if not explicitly.

No, it is interpretation independent. It is older than the MWI.

Then I don't understand what you mean. Can you quote the relevant part from the paper, or specify precisely the part of the paper where it is explained?

 

[Sambuco]

Are you saying that relational QM has a clear ontology? If you do, what is it?

RQM proposes an event-based ontology, in which information is exchanged between different physical systems. However, this raises the question of the existence of physical systems themselves, independent of events. On this point, there is no consensus as discussed in this paper. Some argue that physical systems are also fundamental elements of the interpretation, while others suggest the possibility that physical systems arise from events. Personally, I prefer the second interpretation. I believe that the idea that physical systems are permanent entities that must exist at every instant in time is nothing more than a metaphysical prejudice that arises from our everyday experience.

Lucas.

 

[Sambuco]

I don't think that that's what the relational interpretation says. The crucial issue is the interpretation of entanglement, because particles can be entangled even when they do not interact.

Within RQM entanglement represents the information a physical system possesses about the correlations that may exist in the outcomes of certain future interactions, given some available information about past interactions. In other words, entanglement is a property associated with the probability of transition between different events. Of course, this is still somewhat "weird," since the events involved may be space-like separated. Several interpretations of this are discussed in section 3 and 4 of this paper.

The relational interpretation says that entangled particles exist relative to each other.

Entanglement between two particles also exists in relation to a third system. For example, in Wigner's friend experiment, he assigns an entangled state to the friend+system.

I don't see how relative existence provides a clear ontology.

At the end of the day, and as with other interpretation, whether or not this constitutes an "acceptable" ontology is, so to speak, a matter of personal preference.

Lucas.

 

[martinbn]

No, I mean the Bell's $\lambda$.

But isn't that the hidden variables? It seems that for you if the interpretation doesn't have HV it has no clear ontology. That is strange use of terminology. Why not simple say that there are no HV in that interpretation!?

I think it is implicitly, if not explicitly.

I am no sure about that, but in any case I don't see the connection with ontology. For me relativity, block universe or not, has the same ontology as classical physics.

Then I don't understand what you mean. Can you quote the relevant part from the paper, or specify precisely the part of the paper where it is explained?

It starts in the right column on page 9. He credits Neville Mott 1929.

 

[PeterDonis]

Entanglement between two particles also exists in relation to a third system.

No, it doesn't. It's a property of the joint quantum state of the two particles (that it can't be factorized into a product of states of each particle individually). It has nothing whatever to do with any third system.

 

[PeterDonis]

in Wigner's friend experiment, he assigns an entangled state to the friend+system.

No, the specification of the experiment assigns an entangled state to the friend + system once they have interacted, because of the unitary dynamics of the interaction. Wigner simply assumes that there is no actual, physical collapse of the wave function, so that the friend's "measurement" of (i.e., interaction with) the system doesn't collapse anything, it just produces the entangled state. But that state has nothing whatever to do with Wigner: it's just unitary dynamics of the interaction plus no collapse.

 

[Sambuco]

No, it doesn't. It's a property of the joint quantum state of the two particles (that it can't be factorized into a product of states of each particle individually). It has nothing whatever to do with any third system.

When I say "in relation to a third system" I'm talking about the relational interpretation, where the entanglement between two physical systems ("system" and "friend" in Wigner's friend experiment) can only exist with respect to a third system ("Wigner") for which the system-friend interaction is unitarily represented. That's what I was referring to.

No, the specification of the experiment assigns an entangled state to the friend + system once they have interacted, because of the unitary dynamics of the interaction. Wigner simply assumes that there is no actual, physical collapse of the wave function, so that the friend's "measurement" of (i.e., interaction with) the system doesn't collapse anything, it just produces the entangled state. But that state has nothing whatever to do with Wigner: it's just unitary dynamics of the interaction plus no collapse.

No. In RQM, it is not possible to assign a quantum state to a physical system, unless one specifies in relation to which other system (perhaps, an observer) the system under study is being described.

Lucas.

 

[Demystifier]

But isn't that the hidden variables?

No. The $\lambda$ is what Bell calls a beable, which does not necessarily need to be hidden.

 

[martinbn]

No. The $\lambda$ is what Bell calls a beable, which does not necessarily need to be hidden.

Ok, the additional variables. I meant hidden in this sense, that they are not part of the QM formulation. I thought this was the standard termonology. Anyway, why do you call an interpretation that has no additional variables an intepretation with no clear ontology and not an interpretation with no additional variables.

 

[martinbn]

RQM proposes an event-based ontology, in which information is exchanged between different physical systems. However, this raises the question of the existence of physical systems themselves, independent of events. On this point, there is no consensus as discussed in this paper. Some argue that physical systems are also fundamental elements of the interpretation, while others suggest the possibility that physical systems arise from events. Personally, I prefer the second interpretation. I believe that the idea that physical systems are permanent entities that must exist at every instant in time is nothing more than a metaphysical prejudice that arises from our everyday experience.

Lucas.

This is hard to understand. What does it mean for the physical systems not to exist at all times? If they don't exist at a given time, then don't we just have an empty space-time? Why would they start to exist later on?

I can understand what it means for the physical systems not to be fundamental. I am strugling with the non-existence.

 

[Demystifier]

Ok, the additional variables.

No. The beable does not need to be an additional variable. For example, in the many world interpretation the beable $\lambda$ is the wave function $\psi$.

The beable of an interpretation is the thing that physically exists even when it is not measured. For example, when you say that particle exists even when it is not measured, then particle is supposed to be the beable in your interpretation. However, the problem with your interpretation is that your beable is not represented by a mathematical object. In particular, it cannot be a wave function, because an entangled 2-particle wave function does not represent a single particle. The beable $\lambda$ must be represented by a mathematical object, otherwise it is not well defined.

 

[martinbn]

No. The beable does not need to be an additional variable. For example, in the many world interpretation the beable $\lambda$ is the wave function $\psi$.

You started with the "state of existence". I asked you if that was the state of the system. You said "No, the Bell's $\lambda$". Now you say that it can be the wave function, which is the state of the system!

Did you have a look at Mott's argument? What do you think about it?

 

[Demystifier]

You started with the "state of existence". I asked you if that was the state of the system. You said "No, the Bell's $\lambda$". Now you say that it can be the wave function, which is the state of the system!

"Is" and "can be" are not the same thing. But you didn't respond to my objection that your notion of "particle", as an object that exists even when it is not measured, is not defined mathematically.

Did you have a look at Mott's argument? What do you think about it?

I have looked at it, but haven't understood it.

 

[martinbn]

But you didn't respond to my objection that your notion of "particle", as an object that exists even when it is not measured, is not defined mathematically.

Are referring to the first paragraph in post #9? I responded to it. Or is this from another thread?

 

[martinbn]

"Is" and "can be" are not the same thing.

Ok, so for you an interpretation doesn't have a clear ontology unless the state of the systems is ontological (whether if is #\psi## or something else). Is that right?

 

[Demystifier]

Are referring to the first paragraph in post #9? I responded to it. Or is this from another thread?

I mean this thread, post #25.