I What makes the interpretations of Quantum Mechanics so important?

[Quanundrum]

The bare theory has no way of making the other elements of the superposition disappear.

If you assume the bare theory is fundamental, then indeed, but you do not get splitting worlds from this without additional assumptions, rendering it on par with Bohmian Mechanics and GRW

 

[Michael Price]

If you assume the bare theory is fundamental, then indeed, but you do not get splitting worlds from this without additional assumptions, rendering it on par with Bohmian Mechanics and GRW

Reference?

 

[Mentz114]

The bare theory has no way of making the other elements of the superposition disappear.

How can one prove they existed at all ? MWI is all speculation.

 

[Michael Price]

How can one prove they existed at all ? MWI is all speculation.

You need the all the elements in a superposition to make physics work at the microscale. If you're saying the laws of physics don't extrapolate to the macroscale, you'll need a dawn good reason to convince me.

 

[Mentz114]

You need the all the elements in a superposition to make physics work at the microscale.

MWI needs macroscopic superpositions as well, if I recall correctly.

If you're saying the laws of physics don't extrapolate to the macroscale, you'll need a darn good reason to convince me.

Huh ?
No, I'm saying MWI is not the laws of physics.

[edit]
@Michael Price - reading this I think am expressing my skepticism rather disrespectfully considering that you have studied these things to a level I cannot reach. I will let it rest and refrain from what are probably nit-picking objections.

 

[PeterDonis]

What follows Quantum Theory minus the Collapse Postulate is the 'Bare Theory' not MWI though.

Please give a reference for the "Bare Theory". I have only seen it used in philosophy books (and ones for lay people, not textbooks), such as Albert's Quantum Mechanics and Experience (at least I think that's the one where he uses that term).

 

[Quanundrum]

Please give a reference for the "Bare Theory". I have only seen it used in philosophy books (and ones for lay people, not textbooks), such as Albert's Quantum Mechanics and Experience (at least I think that's the one where he uses that term).

I am traveling atm. so pulling up references is cumbersome. Simply google: "Bare Theory" + "Jeffrey Barrett" and you will find the most comprehensive literature on both Everett's original thesis, as well as what David Albert indeed coined as 'Bare Theory'

 

[PeterDonis]

Simply google: "Bare Theory" + "Jeffrey Barrett"

This turned up a number of papers, including this one:

http://www.socsci.uci.edu/~jabarret/bio/publications/FixBareTheory.pdf
However, I'm not finding any actual physicists who either advocate for or use the "bare theory", only philosophers discussing it.

 

[Quanundrum]

This turned up a number of papers, including this one:

http://www.socsci.uci.edu/~jabarret/bio/publications/FixBareTheory.pdf
However, I'm not finding any actual physicists who either advocate for or use the "bare theory", only philosophers discussing it.

The same goes for MWI :)

 

[PeterDonis]

The same goes for MWI :)

One could say that physicists don't "use" any particular interpretation to actually analyze experiments, other than the minimal "shut up and calculate" interpretation, but many physicists have written papers on the MWI. That's why I was wondering if any physicists had written papers on the Bare Theory.

 

[Michael Price]

MWI needs macroscopic superpositions as well, if I recall correctly.

Huh ?
No, I'm saying MWI is not the laws of physics.

[edit]
@Michael Price - reading this I think am expressing my skepticism rather disrespectfully considering that you have studied these things to a level I cannot reach. I will let it rest and refrain from what are probably nit-picking objections.

I simply say that MWI is the extension of the microscale laws.to the macroscale, and leave it there.

 

[forcefield]

I simply say that MWI is the extension of the microscale laws.to the macroscale, and leave it there.

How does that relate to saying that there is a nearly infinite number of laws that change when the scale (or size/complexity) changes until Newton's laws ?

 

[Michael Price]

How does that relate to saying that there is a nearly infinite number of laws that change when the scale (or size/complexity) changes until Newton's laws ?

The laws don't change with the scale.

 

[forcefield]

The laws don't change with the scale.

From the Feynman Lectures here: "As we apply quantum mechanics to larger and larger things, the laws about the behavior of many atoms together do not reproduce themselves, but produce new laws, which are Newton’s laws, which then continue to reproduce themselves from, say, micro-microgram size, which still is billions and billions of atoms, on up to the size of the earth, and above."

 

[Michael Price]

From the Feynman Lectures here: "As we apply quantum mechanics to larger and larger things, the laws about the behavior of many atoms together do not reproduce themselves, but produce new laws, which are Newton’s laws, which then continue to reproduce themselves from, say, micro-microgram size, which still is billions and billions of atoms, on up to the size of the earth, and above."

He doesn't mean what you think he means.

 

[forcefield]

He doesn't mean what you think he means.

I can only guess what he means by the "quantum laws" and even then only vaguely. Could you please elaborate on my question then ?

 

[bhobba]

It's not bizarre, it's simply a misleading formulation you read quite often. I've never understood what the intention of the authors making it may be. It's said "a quantum state can be in a superposition". That's just a meaningless intellectual-sounding phrase.

That it must be so (ie a vector space) is even intuitive. Simply start with the idea a system is described in some way by a function. Especially when extended to Rigged Hilbert space virtually any function is an element of such a space eg take any two functions and its sum is another function, multiply it by c and it is also a function. Viewed this way it would strange its NOT a vector space. The real issue is the functions are complex - why is that? There is an answer but rather than me say it people might like to try a little research:
https://www.scottaaronson.com/democritus/lec9.html
Now how does probability come into it? Well there is this theorem called Gleason:
http://kiko.fysik.su.se/en/thesis/helena-master.pdf
You may not be able to spot the hidden assumption - I didn't when I first studied it. But then you read Weinberg, who, correctly says - the Born Rule can't be derived from within QM - so trusting someone like Weinberg you go looking for it. There are in fact a couple but the main one is non-contextuality. So you have this other assumption - non- contextuality. Its quite intuitive, but its an assumption. What if we reject it. That is the path that leads to things like DBB etc.

That is the purpose of interpretations - it illuminates exactly what is being assumed and what different assumptions lead to. Will it lead to progress? It already has - the essence of Non Contextuality is in the so called Kochen-Specker theorem (but not emphasized enough its a simple corollary to Gleason).

Interpretations are not a popular research area - it gets most of its traction on the internet - but progress is being made. But at a slow pace and as I have posted before I nowadays do not think it will in the end help in progressing Quantum Theory - it still has issues like quantum gravity, the triviality of QED (the whole standard model - excluding gravity - may in fact be trivial) plus other issues. To me moving that forward will be of greeter value. But of course science often does surprise.

Thank
Bill

 

[bhobba]

The laws don't change with the scale.

True - but their approximation valid at the larger scale can be different.

Thanks
Bill

 

[Michael Price]

True - but their approximation valid at the larger scale can be different.

Thanks
Bill

Yes, absolutely.

 

[vanhees71]

The laws don't change with the scale.

That's for sure not true. Not a single piece of physics is scale invariant according to the Standard Model of HEP!

 

[Michael Price]

That's for sure not true. Not a single piece of physics is scale invariant according to the Standard Model of HEP!

That is a different issue, and has nothing to do with the universality of quantum physics.

 

[vanhees71]

I also don't understand what scaling invariance should have to do with the universality of quantum physics. I just wanted to point out that the claim that anything is scaling invariant is simply wrong.

 

[Sophrosyne]

Summary: Provided it's correct that the interpretations of Quantum Mechanics can be neither proved nor disproved why then do researchers invest so much time and talent in this field?

How valid is the statement "It means physics is ultimately concerned with descriptions of the real world" in the realm of QM? Heretic question, what is "real" besides the outcome of the measurement?

I think what makes people uncomfortable is not understanding WHY it acts the way it does; not understanding the underlying mechanism. Wanting to know WHY something acts the way it does is not a bad question. It's perfectly reasonable. We may not be in a position to answer it yet, but that doesn't mean we can't keep asking it. Until then though, we are still just left with Feynman's "shut up and calculate" interpretation. It's all we got for now. But that's no reason to think that's all there is to it.

Who knows, maybe once we figure out the mechanism of why quantum mechanics works the way it does, it will open up very interesting new worlds and possibilities, and a whole bunch more questions.

What is clear is that we don't understand everything there is to understand about this stuff yet. Like Feynman said, learning to live with such discomfort of not knowing everything is part of being a scientist, and what keeps science always growing.

"The scientist has a lot of experience with ignorance and doubt and uncertainty, and this experience is of very great importance, I think...If we take everything into account — not only what the ancients knew, but all of what we know today that they didn't know — then I think that we must frankly admit that we do not know.
But, in admitting this, we have probably found the open channel.This is not a new idea; this is the idea of the age of reason. This is the philosophy that guided the men who made the democracy that we live under. The idea that no one really knew how to run a government led to the idea that we should arrange a system by which new ideas could be developed, tried out, and tossed out if necessary, with more new ideas brought in — a trial and error system. This method was a result of the fact that science was already showing itself to be a successful venture at the end of the eighteenth century. Even then it was clear to socially minded people that the openness of possibilities was an opportunity, and that doubt and discussion were essential to progress into the unknown. If we want to solve a problem that we have never solved before, we must leave the door to the unknown ajar...

Now, we scientists are used to this, and we take it for granted that it is perfectly consistent to be unsure, that it is possible to live and not know. But I don’t know whether everyone realizes this is true. Our freedom to doubt was born out of a struggle against authority in the early days of science. It was a very deep and strong struggle: permit us to question — to doubt — to not be sure. I think that it is important that we do not forget this struggle and thus perhaps lose what we have gained."
-Richard Feynman

Don't stop asking the questions, but be careful not to jump on any answer just because you have to have one. If we still don't know, it's OK to just leave the question open.

 

[timmdeeg]

Who knows, maybe once we figure out the mechanism of why quantum mechanics works the way it does, it will open up very interesting new worlds and possibilities, and a whole bunch more questions.

Wouldn't this imply a proof that e.g. Many Worlds really exist or that the wave function really collapses?

 

[RUTA]

Wouldn't this imply a proof that e.g. Many Worlds really exist or that the wave function really collapses?

I think an experiment like this one would have implications https://arxiv.org/abs/1705.04620

 

[PeterDonis]

I think an experiment like this one would have implications

It would certainly have implications if (admitted to be highly unlikely by the author) results were obtained that obeyed the Bell inequalities and disagreed with the predictions of QM.

I don't see what implications (other than "oh, well, QM is confirmed again") it would have if the results were that the Bell inequalities were violated and everything was just the same as in previous experiments.

 

[RUTA]

It would certainly have implications if (admitted to be highly unlikely by the author) results were obtained that obeyed the Bell inequalities and disagreed with the predictions of QM.

I don't see what implications (other than "oh, well, QM is confirmed again") it would have if the results were that the Bell inequalities were violated and everything was just the same as in previous experiments.

I’m thinking Kim et al delayed choice quantum eraser where the decision to erase or not is made by a human. That would have implications either way

 

[DarMM]

What would be the implications if it went the other way? As in over Tsirelson's bound.

 

[RUTA]

What would be the implications if it went the other way? As in over Tsirelson's bound.

I don’t know of any theory predicting that

 

[PeterDonis]

I’m thinking Kim et al delayed choice quantum eraser where the decision to erase or not is made by a human. That would have implications either way

Why would it have implications either way? If all that happens is that the predictions of QM are confirmed, what implications does that have?