Shortcomings of quantum theory

[woolyhead]

What do members think of the idea that the philosophy which began quantum theory in the first place was inadequate to explain and describe reality in a sufficiently deep way, so that we now have a theory which in many ways fails to describe the reality which we experience in the world?

 

[tom.stoer]

There was no philosophy of quantum mechanics which misguided physicists. There were some classical concepts (and related philosophical reasoning) which were unable to explain the quantum world. So instead of keeping inadequate classical concepts quantum theory had been invented.

QT has been proven to be the correct decription of nature, in the sense that its predictions agree with experimental results (or al la Popper: no experimental falsification of QT predictions has been observed).

At a later stage one tried to establish philosophical reasing, adjusting certain philosophical concepts etc.

So it is NOT the case that QT fails to describe reality! It's the other way round: our classical concepts regarding "reality" DO NOT FIT to the quantum world. It's nature that tells us that our classical philosophical concepts failed!

 

[arkajad]

And which philosophy was ever adequate?

 

[tom.stoer]

And which philosophy was ever adequate?

Any interpretation of QM is adequate in the sense that it respects proven facts. But that does not mean that these interpretations are adequate in a philosophical sense. Personally I accept QM as a theory describing nature, but don't LIKE any interpretation I have seen so far.

 

[arkajad]

Who cares about "philosophical sense". And what it is anyway? There are as many "philosophical senses" as there are philosophers, and probably many more.
Instead of talking generalities ask a particular question and perhaps someone who knows the subject will answer your question.

 

[tom.stoer]

Did you aks me? or woolyhead?

Anyway, you seem to believe in the shut-up-and-calculate philosophy. But even this IS a philosophy, so there's no escape.

OK, here's my question: does the moon exist even if nobody is looking at it?

 

[arkajad]

"does the moon exist even if nobody is looking at it?"

What it has to do with the title of this thread which is not astronomy but quantum theory? Ask astronomers and they will laugh at you.

 

[tom.stoer]

The question is just a warm up for the next one: does an electron exist even if there's no measurement observing it?

It is just to exemplify that there are questions which may seem to be ridiculous in a physical (positivistic) context but which deserve philosophical reasoning. Remember: the first question in this thread was about quantum mechanics and philosophy.

 

[DevilsAvocado]

What do members think of the idea that the philosophy which began quantum theory in the first place was inadequate to explain and describe reality in a sufficiently deep way, so that we now have a theory which in many ways fails to describe the reality which we experience in the world?

Welcome to PF woolyhead!

I understand what you mean, but I think that the "shortcomings" you are talking about, depends on what you set out to achieve from the beginning. This was the scientific goal for Niels Bohr:

"It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about nature."

"Our task is not to penetrate into the essence of things, the meaning of which we don’t know anyway, but rather to develop concepts which allow us to talk in a productive way about phenomena in nature."

"There is no quantum world. There is only an abstract quantum physical description."​

Now, to me it seems a little 'peculiar' if we happened to live in that century which had fastest technological revolution (so far), and besides that – found the final answers of everything.

I don’t make sense...

And we know it don’t make sense since Einstein’s General Relativity is not 100% compatible to Quantum Mechanics. One or both must be slightly 'incomplete'. That’s a fact.

This by no means indicates that QM is wrong. In fact, QM is the most precise theory we got. But to make a parallel; before Einstein’s relativity, Newton’s law on gravity was the only one, and it worked (almost) perfectly... and then Einstein came up with his theory, that is 100% backward compatible to Newton gravity, but makes new predictions about 'extreme' situations.

My guess is that we will see something similar in the future, in a new theory that will merge QM & GR, and be 100% "backward compatible".

 

[tom.stoer]

I think the question was not about physical shortcomings of QM (there aren't any, except perhaps for quantum gravity) but a clash of quantum mechanics and "reality which we experience".

 

[arkajad]

does an electron exist even if there's no measurement observing it?

Exists? Please, define "exists" in this particular context.

 

[tom.stoer]

"Exist" in just the same way as the moon exists even if nobody is looking at it.

 

[arkajad]

This is not the same context. Electron can not exist in "the same sense" as Moon exists. But why do you have doubts about existence of electrons? They have mass, they have charge, they have spin, they are just tiny-ting and hard to observe the same way as you observe the Moon. And when you say "nobody is looking", you mean "human being"? Will a cat count? Or a frog?

 

[tom.stoer]

I just want to clarify that there are philosophically reasonable questions outside the physical world.

You say that the context for the moon and for the electron is different - why? Both are physical objects, both have mass, charge, angular momentum etc. Both can be described by quantum mechanics in principle (even so for teh moon it's rather complicated).

The problem is that "existence" cannot be defined within physics. If you define "existence" in a positivistic sense (according to phenomenology) than you cannot explain why "objects" can exist even if nobody is looking at them. If you define existence in an ontological sense then you must explain what existence means beyond phenomenology.

In quantum mechanics you cannot define the "existence of an electron". All you have are state vectors and operators. But an electron IS neither an operator nor a state vector. It can be DESCRIBED by a state vector but it certainly IS not a state vector. So the question is what this IS means.

This has been discussed by Einstein, Bohr, Heisenberg, Schrödinger, Bohm, Wigner, Popper to mention just a few. They all agreed on the mathematical foundations of quantum mechanics, how to apply them in order to make physical predictions. But they did not agree on "existence", "IS", "realism" etc.

I do not doubt that the electron exists, but I insist on the fact that neither you nor me can explain what it MEANS that the electron EXISTS. That's beyond physics.

 

[arkajad]

In quantum mechanics you cannot define the "existence of an electron". All you have are state vectors and operators.

Well, that depends on which quantum mechanics. There are variants. Does space and time exist in quantum mechanics? They are not state vectors and operators. Yet few people doubt that they exist. On the other hand in Bohm's version electron exists and moves along a nonclassical trajectory. Which particular version will give a better agreement with observations is yet to be seen. Different formalisms are still under development.

 

[GeorgCantor]

Who cares about "philosophical sense". And what it is anyway? There are as many "philosophical senses" as there are philosophers, and probably many more.
Instead of talking generalities ask a particular question and perhaps someone who knows the subject will answer your question.

The question is that NOBODY(esp. you) knows the answer to the question how qm relates to the world outside. You can keep asking and advising others to ask, but this can only serve to kill time and so that it passes by.

 

[GeorgCantor]

Well, that depends on which quantum mechanics. There are variants.

These 'variants' are just pure hypothesises and idle speculation. Do you understand that there is a difference between "knowledge" and "speculation"?

Does space and time exist in quantum mechanics? They are not state vectors and operators. Yet few people doubt that they exist.

You have a LOT more to learn before ou can make such sweeping generalizations, as to who doubts what.

On the other hand in Bohm's version electron exists and moves along a nonclassical trajectory.

It's still a classical-like trajectory.What's your point?

Which particular version will give a better agreement with observations is yet to be seen. Different formalisms are still under development.

I think you need to tone down your statements towards Tom(an actual physicist), as he's way more knowledgeable than you. The different formalism that you seem to imply has trouble with relativity and places ALL the mystery of qm into the pilot wave, thus 'removing' the other mysteries. If you are advocating this approach, be warned that it's not considered quite mainstream science here by the mentors.

"does the moon exist even if nobody is looking at it?"

What it has to do with the title of this thread which is not astronomy but quantum theory? Ask astronomers and they will laugh at you.

Astronomers are the last group of physicists who'd be qualified to take on this question.

This is not the same context. Electron can not exist in "the same sense" as Moon exists. But why do you have doubts about existence of electrons? They have mass, they have charge, they have spin, they are just tiny-ting and hard to observe the same way as you observe the Moon.

So what that electrons have charge, mass and spin AT measurements? What is that supposed to tell us about unmeasured, superpositional electrons? Does it make sense to think that you are the first person to propose common-sense lay reasoning to iron out the paradoxes of the quantum world?

 

[arkajad]

The question is that NOBODY(esp. you) knows the answer to the question how qm relates to the world outside.

Quantum mechanics is a theory formulated by human beings in order to describe the world outside. So it relates by its very construction.

 

[GeorgCantor]

Quantum mechanics is a theory formulated by human beings in order to describe the world outside. So it relates by its very construction.

The question is:

What does its construction say about the world of cars and Moons(on top of giving us predictions about measurements)?


If you don't have means to prove empirically what you want to propose as the True interpretation(which of course you don't), leave the others(esp the more knowledgeable) to ponder what it all means for the world outside. There are some of us that love to hear their considerations.

 

[arkajad]

If you are advocating this approach, be warned that it's not considered quite mainstream science here by the mentors.

Mainstream science? What is your definition of this term? Don't you know that the standard qm has also troubles with relativity?

 

[GeorgCantor]

Mainstream science? What is your definition of this term?

It's not my business to tell the moderators what should be mainstream science. It's their site, they are in charge of what is credible and what is not. A pilot wave that acts in a godly fashion is a controversial idea to most.

Don't you know that the standard qm has also troubles with relativity?

I do know that most don't(transactional, relational, most versions of the ci, some versions of mwi, the many-minds, etc.). Do you actually know of a deterministic and nonlocal interpretation besides BM?

The troubles between qm and relativity are more related to realism than between the CI and GR.

 

[arkajad]

Do you actually know of a deterministic and nonlocal interpretation besides BM.

Why would you insist on it being deterministic? For which reason? But if you give up determinism, you may like to check


http://arxiv.org/abs/quant-ph/9906034"

It's mainstream science: Phys. Rev. A!

 

[GeorgCantor]

Why would you insist on it being deterministic? For which reason?

A "nonlocal deterministic theory" is the same as a "nonlocal realistic theory". It's sort of like:

"arkajad posted this message" and "this message was posted by arkajad"

But if you give up determinism, you may like to check


http://arxiv.org/abs/quant-ph/9906034"

It's mainstream science: Phys. Rev. A!

I'll have a look at the paper later today, when i hopefully will have more spare time.

 

[JDStupi]

Quantum mechanics is a theory formulated by human beings in order to describe the world outside. So it relates by its very construction.

That. Here we have a statement of purpose, many things have been constructed to describe the world outside, and fail, so we cannot simply say that "by construction" it relates. What is true, though, is that QM does construct mathematical formalisms that are purported to describe external reality and it just so happens that, to an extent, they do. The question is why, how, and what does this tell us about human knowledge, inquiry and science? We use these "philosophical" questions for consideration and possible brewing of a new perspective, and I don't see the reason some people are so hostile toward a "non-scientific" avenue for thoughts. Rather than try to fight off these ideas just think about them and say "hmmm" What is existence? It is a vague notion isn't it? What does this say?

Not many doubt space and time, because they reveal themselves in our conscious experience itself, electrons on the other hand do not.

Finally, do not take this as a statement of position, personally I do not know enough about QM specifics to take a position, which is why right now I"m fairly indeterminate in my considerations (pun unintended).

 

[arkajad]

What is existence? It is a vague notion isn't it?.

You want to know the truth, don't you? But first ask what is TRUTH? Those searching for truth deep enough meet paradoxes. In "Saving truth from paradoxes" Hartry Field suggests that, perhaps, we need to weaken the classical logic. Is some kind of quantum logic a solution? Perhaps...

 

[apeiron]

You want to know the truth, don't you? But first ask what is TRUTH? Those searching for truth deep enough meet paradoxes. In "Saving truth from paradoxes" Hartry Field suggests that, perhaps, we need to weaken the classical logic. Is some kind of quantum logic a solution? Perhaps...

Your comment that QM relates to reality via its construction is indeed the right way to think about it. It is a model that generates predictions/measurements. And these in turn confirm the model. So there is "truth" in the process.

People who study modelling as a process - epistemology/modelling relations - will also say that paradoxes are a feature of models because "good models" are closed systems of logical entailment. Once their axioms are granted, they have deductive certainty. But being closed, they also have by necessity crisp limits. Where they become self-referential, they will appear paradoxical.

So do we need a quantum logic to replace classical logic?

Again, those who have been wrestling with modelling theory in other areas of science - mind science and theoretical biology - would say good modelling is good modelling. If it works, it ain't broke. Agonising about truth and completeness is a false path. There is not some greater model that will come along and invalidate existing models in a simplistic way because paradoxes are evidence of something good in a model - causal closure.

However, there is indeed a "larger" way of modelling than the mechanical or computational paradigm that is "classical logic". And that would be a systems logic, or a holistic logic.

This would also be a "quantum" logic potentially in my view.

But again, the reaction needs to be balanced. There is already quite a literature on the nature of modelling, the reasons why self-reference leads to paradoxes, and why this is really a symptom of success more than failure.

The more contentious issue is whether a larger model of reality will come from "deeper" - that is from the smaller-scale substrate - or instead from the other direction, from a more holistic viewpoint.

Most people in physics talk as if they expect the next level of modelling to be sub-planckian. So they want to reduce GR to "QM scale". They want to reduce reality to the fine-grain substances like strings or loops.

Yet at the same time, a lot of the modelling is also holistic. LQG is meant to be background independent (and so able to weave its own metric). Condensed matter physics thinking is becoming increasingly important. Event horizons are again a way of thinking about the whole determines its parts.

I don't know if this is a proper analogy but it seems like that those who see QM as an impenetrable mystery are like those old flat Earth maps where the seas just drop off an edge into nothing. The fact that classical physics has boundaries is treated as a rupture, a catastrophe, when really the world is round and, likewise, good models have causal closure.

QM clearly seems an open model in key regards. The collapse by an "observer" still has to be inserted informally by hand and is not part of the model. But it is a closed model if you push that collapse issue to the margins - as with MWI and other "no collapse" interpretations for example.

So yes, a larger model seems possible - one that includes the very self-referential issue of the collapse. And decoherence seems the way to go on answering this - a holistic systems approach. But QM itself seems closed in its own terms, just as classical models are also closed in their own terms.

So nothing seems fundamentally broke about our modelling of reality, and the future direction for progress also seems pretty clear.

 

[arkajad]

However, there is indeed a "larger" way of modelling than the mechanical or computational paradigm that is "classical logic". And that would be a systems logic, or a holistic logic.

Some work in this direction is being done. You may like to check
"[URL
A Gravitational Explanation for Quantum Mechanics[/URL] by Mark J. Hadley

From the Abstract:

``It is shown that certain structures in classical General Relativity can give rise to non-classical logic, normally associated with Quantum Mechanics. A 4-geon model of an elementary particle is proposed which is asymptotically flat, particle-like and has a non-trivial causal structure. The usual Cauchy data are no longer sufficient to determine a unique evolution. The measurement apparatus itself can impose non-redundant boundary conditions. Measurements of such an object would fail to satisfy the distributive law of classical physics. This model reconciles General Relativity and Quantum Mechanics without the need for Quantum Gravity.''​