Interpretations of QM? What is nature really like?

[ZapperZ]

How about this then Zapper?

http://www.math.rutgers.edu/~oldstein/papers/zei.pdf

Quantum theory has always invited rather extreme speculations about the nature of
physical reality. John Wheeler [1], for example, famously conjectured that quantum
mechanics suggests a “participatory universe” in which the present observations of
experimentalists can give “tangible reality” to the distant past, that current actions
can somehow produce the past physical structure of the universe, rather than merely
inform us about it...

Unfortunately, when the topic of discussion is quantum theory, basic standards of clarity and argumentation seem to be abandoned, even in the most prestigious journals.

To the best of your knowledge, is it true that John Wheeler made this speculation, and is it true that QM standards of clarity/argumentation are deficient?

I have no idea. I'm sure if you have followed this thread (and any other previous threads related to this) that I have very little patience with such "interpretations". Why? Unless one can make measurable predictions that can validates one's claim, all of these things are nothing more than a matter of tastes, or what Sheldon Glashow would say "it isn't physics, it's philosophy".

You may want to ask someone else on here regarding this. Discussing "philosophical" implications is not my favorite activity.

Zz.

 

[Farsight]

OK.

Anybody: is Quantum Mechanics full of crackpots?

 

[ttn]

Anybody: is Quantum Mechanics full of crackpots?

Definitely. And Niels Bohr is their king.

BTW, the paper about zeilinger that you linked to is spectacular.

 

[Farsight]

I'd better read it then, ttn!

 

[Farsight]

I read it.

It's interesting that Nature refereeing is arguably weak in this area.

 

[MaverickMenzies]

Does quantum mechanics require an interpretation? I have come to regard quantum mechanics as a theory of measurements - i.e. a physics of measurement devices. What i think is quite interesting about quantum mechanics is that it forces us to review our definition of "measurements" and measuring devices.

 

[selfAdjoint]

Does quantum mechanics require an interpretation? I have come to regard quantum mechanics as a theory of measurements - i.e. a physics of measurement devices. What i think is quite interesting about quantum mechanics is that it forces us to review our definition of "measurements" and measuring devices.

The main reason that "shut up and calculate" is so popular is that all the attempts to go beyond it seem to belong on the "Fantasy and Science Fiction" shelf. It is an entirely reasonable position to say that the technology we have -QM - simply does not address questions of ontology and to use it for such is like using a screwdriver to open a can of paint. You don't get the can open and you likely break the screwdriver in the process.

Not that I myself can resist the impulse. I am currently in a discussion with vanesch on another forum concerning the relative merits of RQM, which I kind of like, versus MWI which he so ably represents.

 

[nrqed]

I have no idea. I'm sure if you have followed this thread (and any other previous threads related to this) that I have very little patience with such "interpretations". Why? Unless one can make measurable predictions that can validates one's claim, all of these things are nothing more than a matter of tastes, or what Sheldon Glashow would say "it isn't physics, it's philosophy".

You may want to ask someone else on here regarding this. Discussing "philosophical" implications is not my favorite activity.

Zz.

what is intriguing and fascinating is the possibillity that all those "philosophical" debates may actually lead to some actual experimental prediction. From what I have read, it seems to me that this was the prevalent view about the "hidden variables vs QM" prior to Bell's breakthrough... that the debate belonged more to philosophy than to physics.

 

[ZapperZ]

what is intriguing and fascinating is the possibillity that all those "philosophical" debates may actually lead to some actual experimental prediction. From what I have read, it seems to me that this was the prevalent view about the "hidden variables vs QM" prior to Bell's breakthrough... that the debate belonged more to philosophy than to physics.

I'm sure it was. I even called such a debate before Bell as simply a matter of tastes.

However, it was when Bell came up with such a theorem to test it did it come back into the realm of physics. But to attribute the cause of it as having philosphical origin is rather dubious. That's like saying astrology was responsible for astronomy.

I could also turn it around and point out to the fact that such debates in the first place came out of QM before it became a "philosophical issue".

Zz.

 

[setAI]

what is intriguing and fascinating is the possibillity that all those "philosophical" debates may actually lead to some actual experimental prediction. From what I have read, it seems to me that this was the prevalent view about the "hidden variables vs QM" prior to Bell's breakthrough... that the debate belonged more to philosophy than to physics.

QM is very strange- and up until just a few years ago things were too murky with too many interpretations for any meaningful discussion of phenomenology outside of philosophical speculation- but since the invention of the first quantum logic gates in 1998 we are forced to deal with the MWI and to accept it's implications-

for instance this symposium on Retrocausation was from just last week: http://www.sou.edu/aaaspd/SanDiego2006/Symposia06.html#10

the leaders in the field are now engaged in the process of taking 'quantum weirdness' from philosophy directly to empirical engineering problems-

 

[vanesch]

Does quantum mechanics require an interpretation? I have come to regard quantum mechanics as a theory of measurements - i.e. a physics of measurement devices. What i think is quite interesting about quantum mechanics is that it forces us to review our definition of "measurements" and measuring devices.

Even that, by itself, is a kind of interpretation, no ?

I find several aspects of the interpretational debate rather interesting. The foremost importance is the intuition it helps you to devellop. When you look upon a theory as a black box kind of algorithm out of which comes numbers to be compared with numbers coming out of a data acquisition system, it is hard to get some "physical intuition" for it. You can surely devellop a mathematical intuition for the form of the solutions, that's right.

What I find also interesting, is that quantum mechanics has forced people to make the most crazy statements. I'm often "accused" of making crazy statements myself, but they are an order of magnitude below the craziness of certain very fashionable statements.
The most crazy statement of all is:

1) there IS no underlying reality. Quantum theory is a COMPLETE theory which only describes OBSERVATIONS, and in between THERE IS NOTHING.
Go figure. So before there were observations, there was nothing, in between observations, there's nothing, and it is not said what observations are physically, because there are no "states of matter" or whatever, so no information carriers, or memories or whatever.
Mind you, I'm not talking about any continuity properties of space or time or so. No, I'm indicating the kind of statement that says that things that are not observed, aren't. Are the things that observe, then ?

A close hit is then:
2) On microscopic scales, LOGIC works differently. The concept of truth is flexible.

If truth is flexible, what are we talking about then ? Why is 1 + 1 = 2 in the first place ? Is 1 + 1 only equal to 2 in the macroscopic world, but not in the microscopic world ? What could such a statement even mean ?

What I find surprising is that many people do not seem to have many difficulties in accepting 1) or 2), but seem to refute the very idea that what we observe might be only part of what is. If they can accept 1), then there doesn't even "IS" anything, so what could they care that there is some more of it ? And if they accept 2), why not say that what we observe is both only a part, and everything that "is" (given that logic is supposed to be flawed).

Also, many interpretations of quantum theory do not even allow you to *investigate* into the measurement process, as it is a primary given. How do you investigate into what exactly is a measurement process, if you start by saying that all what exists, are observations ? This is pretty annoying for an instrumentalist ! He always comes too late or too early in the chain to "do the measurement".

That said, we should not forget that all this stuff is about the interpretation of a *theory*. It doesn't have to be related to the real world, which might be entirely different. At the moment, this theory seems to be a rather adequate description of nature, but one day we might see this entirely differently. Only the (far) future can tell.

 

[selfAdjoint]

Also, many interpretations of quantum theory do not even allow you to *investigate* into the measurement process, as it is a primary given. How do you investigate into what exactly is a measurement process, if you start by saying that all what exists, are observations ? This is pretty annoying for an instrumentalist ! He always comes too late or too early in the chain to "do the measurement".

This complaint is not the same as the "there is no reality" one.

For example in our conversation about the RQM interpretation of an Aspect type experiment, on the Beyond the Standard Model... forum, you said that the near observer sees a superposition and the far observer doesn't, and these states have to have enough reality for the observers to compare notes when they get back together. I then evoked the basis problem and we broke off. Let me return to these issues here.

I say that the state vector is not observable and the near observer does not observe that superposition. She infers it on the basis of
1) The experimental setup, which is designed to produce a superposition.
2) Her later comparisons of what she DID observe with what the far observer observed.

But the basis problem says that there is no definite set of numbers describing the near superposition. Rather there is an infinite set of equivalence classes of sets of numbers anyone of which provides a complete description from which the probablility densities of the whole experiment, near and far, can be computed, but no one of which is to be preferred over any other. Near Alice did not see them and cannot remember them. The only thing that has to stay real to do the experiment is the hardware and the observers' memories of what they actually saw. And I think RQM can do that.

And coming back to your paragraph above, I think when you make the innocent proposal to investigate the measurement process you are in fact imputing stable reality to something that does not enjoy mathematical uniqueness.

Einstein faced an analogous problem in GR when he conceived the hole argument. But he had the advantage of tensors whose equations remain stable when you vary the coordinate system. Unfortunately, spinors don't behave that way.

 

[Farsight]

What I find surprising is that many people do not seem to have many difficulties in accepting 1) or 2), but seem to refute the very idea that what we observe might be only part of what is...

Just to let you know, I'm happy with the idea that we observe only a part, vanesch. For example, we can observe the photon's interactions, but we can't observe the photon itself. Just like we can't observe the sunlight that bypasses the moon on a clear night.

For me though there's a big leap between this and MWI. It comes from the meaning of "Universe". This word is of Greek origin, comprising Uni as in unicycle, and verse like in vice versa. It means "turned into one", which equates to "everything". So when I read "parallel universe" or "many worlds" the phrase "many everythings" jumps into my head, and I don't get off first base.

 

[Farsight]

Ah. I've just read what you said on the other thread. Sorry vanesch, I think I should be addressing setAI not yourself.

 

[vanesch]

For example in our conversation about the RQM interpretation of an Aspect type experiment, on the Beyond the Standard Model... forum, you said that the near observer sees a superposition and the far observer doesn't, and these states have to have enough reality for the observers to compare notes when they get back together.

Uh, that's what (I understood) RQM says, not me.

In MWI, this is understood by the fact that *by definition* in MWI an "observer" being a STATE of an observer body, it always sees only one state of itself, but it is entangled with other states: whether these other states are now "observer states" or superpositions thereof makes one say that "the other observer is still in a superposition with respect to this one".

In all this, of course, it depends on what one calls "an observer state", which is, I guess, the "preferred basis problem" you refer to. One way to say what "an observer state" is, is one with a definite entry in a notebook !
As you cannot compare notes of notebooks which are not in "a definite state of notebook", you automatically, when talking about "comparing notes" ASSUME that these states are somehow special.
Now, as I said somewhere else, in how much, these states have some naturalness to them in that they are robust against environmental interaction, and in how much we have to postulate them, is not yet entirely clear for me: if I believe people like Zeh, it seems that environmental decoherence gives them a natural status. But EVEN if I have to postulate them, I do not do anything worse than what's done in RQM, when it is ASSUMED from the start that there are "states of definite knowledge" (namely the vectors of yes/no answers) - which correspond to "definite entry in a notebook" states I referred to above. So, if you don't mind RQM to introduce the *intuitive* concept of "states of knowledge" with a series of definite answers y/n, then you shouldn't object in MWI introducing these states by postulate too. However, if moreover they have some naturalness to them (as indicated by environmental decoherence), then at least we have, in MWI, a *natural* explanation, for an irreducibly intuitive concept in RQM.

So RQM doesn't address any more the "preferred basis" problem than MWI does - but at least MWI has a possible mechanism to it to give some natural explanation for the preferred basis (of definite notebook states).

I say that the state vector is not observable and the near observer does not observe that superposition. She infers it on the basis of
1) The experimental setup, which is designed to produce a superposition.
2) Her later comparisons of what she DID observe with what the far observer observed.

Yes, no problem with that. As we infer the existence of the Earth by looking around us, by seeing pictures of it from satellites etc...

But the basis problem says that there is no definite set of numbers describing the near superposition. Rather there is an infinite set of equivalence classes of sets of numbers anyone of which provides a complete description from which the probablility densities of the whole experiment, near and far, can be computed, but no one of which is to be preferred over any other.

Well, again, I refer to what I said above. Or we have to postulate such a basis (as does implicitly RQM, by giving a special status to these vectors of yes/no answers) where we say that observer states are those with "definite memory states" - or they have some naturalness to them, in that they emerge as the robust states throughout interaction with environment.

Near Alice did not see them and cannot remember them. The only thing that has to stay real to do the experiment is the hardware and the observers' memories of what they actually saw. And I think RQM can do that.

Yes, but by intuitively introducing "observer memory states" (namely vectors of yes/no answers). Let me introduce them as preferred states in MWI too ! We DEFINE observer states as those with definite memory content. But what's (maybe) nice, is that these states ALSO appear as the robust states that "survive" in environmental interaction. So that's maybe the *reason* why we take them as "memory states". If they weren't robust, they wouldn't *keep* their memory, and it would be useless to consider them as "observer memory states", because the very next moment, they'd be gone. So if any "observer experience" which has to stretch over an (even very short) amount of time requires a "robust memory state", then it would be *natural* to have "observer experience states" which relate to states which are robust over (an even very short) amount of time. If we believe the decoherence people, this is exactly what happens: some states (which ressemble classical states) are "robust" against environmental interaction, can hence serve as "memory states" and can hence serve as states associated with observers.

And coming back to your paragraph above, I think when you make the innocent proposal to investigate the measurement process you are in fact imputing stable reality to something that does not enjoy mathematical uniqueness.

No, I hope not. I hope that we can assign "observer status" to certain states by a natural phenomenon (namely stability over time against environmental interaction) ; these states are then "memory states". And we can then investigate how they arise in a specific process.
As I said, I don't know how much "needs to be put in by hand" and how much is "generated naturally", but at least there is some hope to generate it naturally, while in RQM, it is, from the start, put in by hand. So you can't possibly object to that!

Einstein faced an analogous problem in GR when he conceived the hole argument. But he had the advantage of tensors whose equations remain stable when you vary the coordinate system. Unfortunately, spinors don't behave that way.

I don't know if they don't behave that way, when environmental interactions are taken into account. If we believe the decoherence guys, things surely seem to turn out that way.

 

[vanesch]

For me though there's a big leap between this and MWI. It comes from the meaning of "Universe". This word is of Greek origin, comprising Uni as in unicycle, and verse like in vice versa. It means "turned into one", which equates to "everything". So when I read "parallel universe" or "many worlds" the phrase "many everythings" jumps into my head, and I don't get off first base.

That's because you take the colloquial terminology too litterally.
In MWI, there are no "multiple worlds", there is one world (described by the unitary structure made up of the wavefunction/unitary time evolution operator), and there are observers which are states and of which there are very similar copies around, all in slightly (or seriously) different "states of experience".
So MWI should in fact be called "single world with observer experiences which make those observers think they are in a single subworld like they used to think of the entire world classically, but which are in fact different facets of the same, single quantum world" interpretation.

So the SWWOEWMTOTTAIASSLTUTTOTEWCBWAIFDFOTSSQWI