Are physicists happy with Quantum Mechanics as it is?

[stevefaulkner]

Do physicists care whether Quantum Mechanics can be understood? Or are they happy with it as it is so long as they can do calculations with it?

 

[Redd]

I don't think Physicists are ever happy.

But that's just a layman interpretation.

 

[MaxwellsDemon]

Well said Redd, well said. :D

Personally, I'm not too thrilled with the conceptual foundations of the quantum theory. I'd probably laugh it all off as the deluded ravings of brilliant madmen if it weren't for the excellent agreement with experimental observation and sheer number of testable predictions it makes...these compel me to take the theory quite seriously.

 

[stevefaulkner]

I've been working on a project that discovers the source of the philosophical anomalies of Quantum Mechanics. There is a larger set of logical values in quantum mathematics than can be encapsulated by straight Applied Mathematics. Instead, we should be using first-order logic. [nothing to do with approximation methods].

Nevertheless, after all my work, I am beginning to wonder if physicists don't care about it anyway. Thanks for your reply; it is helpful.

Foundations of The Quantum Logic.Steve.

 

[Feldoh]

I think everyone is worried about it a little bit in the back of their mind. However quantum theory has proved very useful in it's current uses.

When it comes down to it the only reason any research is funded is to eventually become something that is useful to society. In this sense we are happy with QM so far.

However most physicists do physics purely for the joy of knowing. In this sense, no they are not happy. They will never be happy until they all know everything (which won't happen)

 

[Winter Flower]

As a person who is currently learning quantum mechanics, it seems like there is still room for something that would make it more intuitive. I am trying to learn the theory without wondering about the philosophical paradoxes too much (since it apparently works). Your project sounds interesting...

 

[ytuab]

Do physicists care whether Quantum Mechanics can be understood? Or are they happy with it as it is so long as they can do calculations with it?

The difficult, mathematical and applied parts of the quantum mechanics(QM) are known better than the introductory parts of QM, I think.
Because in almost all the standard QM textbook, the introductory and historical parts of QM are not explained in detail.

In the process of the Bohr model to the standard QM.
Why doesn't the electron fall into the nucleus radiating energy in standard QM?
The spin is a very strange phenominon of the spinor field.
(The spinor rotation is two-valued, so the spin can not be expressed by the vector field such as real wave flow and real rotation.)
What is the spin of the electron ? Even QFT doesn't answer this fundamental question.
What is the HUP( uncertainty principle)?

I'm wondering why these strange and important phenomina are not explained in detail in the standard QM textbook
(about the physical meaning).


EDIT << alxm, I'm not satisfied if you don't answer the question as below (in the other threads).
Of course, if you say this is a "mathematical" thing, this discussion won't continue..., I think.

A nucleus with a large charge will cause an electron to have a high velocity. A higher electron velocity means an increased electron relativistic mass. These relativistic effects are experimentally showed.
So, the electrons are actually moving fast obeying the probability density of the Schrodinger equation (or other equations which show the probability density) ?
If so, why don't they radiate energy?

If the electrons are not actually moving as the electron clouds, why does the relativistic mass change occur?
In the relativistic theory, the particle's movement in one direction means our (observer's) movement in the opposite direction. So if we (observers) are actually moving in one direction and the relativistic effects of the observed particles are seen,
this means that these effects are caused by the particles' actual movement in the opposite direction?

 

[humanino]

There are a few mathematical details to polish, but I'm pretty happy with decoherence, and I think people who claim it is inconsistent with Bohr's interpretation never talked to him directly.

 

[lmont]

What if...

What if...,
the known universe that we live in was concieved in a particle collider "within" another universe and what we call "dark matter" is merely the effect of a containment field,...and what if what seems like a fraction of a second in the other universe is billions of years inside of our "much" smaller universe.

 

[Phrak]

There are a few mathematical details to polish, but I'm pretty happy with decoherence, and I think people who claim it is inconsistent with Bohr's interpretation never talked to him directly.

Umm. Perchance, have you spoken to Bohr? Or know someone who has? If you have a story to tell, it would be wonderful if you told it.

 

[lmont]

though i won't be around....my guess is that the universe "in which we live", will fly apart and even basic particles ...based on data from particle colliders.

 

[humanino]

Umm. Perchance, have you spoken to Bohr? Or know someone who has? If you have a story to tell, it would be wonderful if you told it.

I just think it's quite unfair to imagine Bohr had a naive view on the so-called problem of measurement.

 

[alxm]

Why doesn't the electron fall into the nucleus radiating energy in standard QM?

How is this a problem with QM? That was the problem with classical physics. The ground state is the ground state and proving that the ground-state is, in fact, the lowest possible energy state is pretty easy. (variational theorem)

You don't even need to explicitly invoke the wave function to show this, since the variational theorem can be reformulated in terms of the electron density (one of the Hohenberg-Kohn proofs) An electronic density more concentrated around the nucleus (or indeed any electronic density that deviates from the ground state density) will have higher energy.

That question is premised on a false, classical-mechanical assumption: That the electron would have lower energy if it was closer to the nucleus.

 

[hamster143]

It comes down to the fact that our "common sense" is a very narrow and imperfect tool for understanding the world. For example, our brains are wired to imagine three-dimensional objects, but we're having serious trouble with four, and five is out of the question. If you can acknowledge this, it's much easier to come to terms with quantum mechanics.

For all we know, the next-level theory behind quantum mechanics could be even weirder.

 

[Fra]

Do physicists care whether Quantum Mechanics can be understood? Or are they happy with it as it is so long as they can do calculations with it?

I think understanding can be established at different levels. Different people may have different opinion of wether the current "understanding" is sufficient, depending on what you use QM for.

A pragmatic approach is to consider QM as a predictive scheme, that has proven it's utility over and over again in a lot of domains. I would expect anyone that thinks QM is exact would not find much sense in a deeper understanding.

But from another angle it's quite obvious that QM does not provide a proven scheme for calculations, this regards it's connection to gravity. Some people think this problem can be solved without changing QM, some don't. There are also several other open questions in physics, where it's a matter of opinon wether the solution will require modification of QM or not.

I personally think that QM is not the last word, I think it's a special case of a more complex model. All the open issues, gravity included, is what motivates me to keep raising this question. But my personal motivation come more from a intellectual quest of wanting to understand my own enviroment.

/Fredrik

 

[Fra]

As a person who is currently learning quantum mechanics, it seems like there is still room for something that would make it more intuitive. I am trying to learn the theory without wondering about the philosophical paradoxes too much (since it apparently works). Your project sounds interesting...

During my first exposure with QM my first reaction was - there has to be a hidden variable explanation. But then there was the Bell's theorem. During my first QM courses, I was quite frustrated by this but as soon as it was apparent that none of, even the in my past judgement better teachers didn't understand this much better in order to explain it, my approach during the courses was to adapt the best possible survival view - the copenhagen view, where the arbitrary choices was to be treated as "facts of science". This was just a survival strategy, otherwise I would have spend all time questioning the formalism, instead of learning how to use it (which is after all the purpose of the course).

However, it's first a little later than I have tried to take on this from perspective, also in the light of gravity, that I see new possibilities. To speak for myself I was not mature at the time of my first QM course to grasp the question I now see.

/Fredrik

 

[Fra]

I think a good flow of perspective, is to first see the historical perspective - WHY classical mechanics fails. Ie. the stability of atoms? the photoelectric effect etc.

So we know at this point that we establisehd that something is wrong about the description of classical physics.

Clearly QM is a possibility there, that solves a lot of questions. But is QM unique?

If you read some of the classical intro books, say Diracs principles of QM, then it's easy to see some of the premises, that are very plausible when you come from classical mechanics (as everyone did when QM was born, so we won't blame them). But in the light of today, a lot of Diracs plausability argumetns are highly questionaly IMO. An alternative reasoning could probably lead to a different model of which QM is a special case.

But I think like Hamster wrote, that this is proably more weird than QM. So reading about the historical development, is probably valuable nevertheless. There is a limit to how large conceptual leaps that anyone can manage.

/Fredrik

 

[Neo_Anderson]

An explination of the problem: Suppose, after Maxwell developed his Law of the Constancy of the Speed of Light (in vacuo), the only way Physicists could reconcile this Law was with the Aether 'theory.' Suppose further that this 'theory' continued unabated, without an Einstein to reconcile Maxwell's Law. The Michleson/Morley experiment is explained away with a modified version of the Aether called the ohr/Sommerfeld Model, in which the Aether moves with the x and y coordinate frames.
There. Aether does not violate the M/M experiment!

But problems arise, such as when radio waves are bounced off the ionosphere; they come back at a time sooner than what the Aether theory predicts.
The Aetherists go back to the drawing board and explain away that the Aether acts as a 'reverse evanescent' energy source for the slowing of the beam in a hypothesis called the Shrodinger/Heisenberg Evanescent Model.
Problem solved! The Aether 'theory' now predicts with 100% accuracy the time dilation shown when radio waves interact with the ionosphere, and with satellites!
Infact, in all aspects of physical action and mechanics, the Aether Theory proves triumphant, predicting physical outcomes and passing test after test!

What is lost? What is reality? What hadn't ever been considered before that would prove with the same level of accuracy as the always-modified Aether? The Special Theory of Relativity.

No. I am in no way, shape or form satasfied with QM.

 

[Demystifier]

Do physicists care whether Quantum Mechanics can be understood? Or are they happy with it as it is so long as they can do calculations with it?

Some of them are happy, and some of them are not. Those who are happy are mainly interested in practical aspects of physics, while those who are not are interested in deep understanding of nature as well.

 

[Bob_for_short]

Some of them are happy, and some of them are not. Those who are happy are mainly interested in practical aspects of physics, while those who are not are interested in deep understanding of nature as well.

I can safely say that nobody understands Classical Mechanics. I mean where CM determinism comes from.

 

[Demystifier]

I can safely say that nobody understands Classical Mechanics. I mean where CM determinism comes from.

You might like this:
http://xxx.lanl.gov/abs/quant-ph/0505143 [Found.Phys.Lett. 19 (2006) 553]

 

[Bob_for_short]

You might like this:
http://xxx.lanl.gov/abs/quant-ph/0505143 [Found.Phys.Lett. 19 (2006) 553]

It is not really what I wanted to underline. In CM we can entirely stay within CM to see where CM determinism comes from. It's easy.

Let us consider a body that is cinsidered as a point in CM. In fact, it is not a just point but a compound system. In its "entire" CM descriprion we naturally use the center of inertia (CI) or center of mass coordinates R(t) and the relative coordinates {r_i}, i = 1-N, N>>1. The relative coordinates are normally oscillating/rotating and exchanging their energy with the envoronement. For example, we see the full Moon due to light emitted with the Moon's internal degrees of freedom. We take many-photon picture, make an average of it and obtain one definite value R(t). The entire concept of space-time in CM implies this multi-photon exchange. Then we forget about the way how we "observe" CM objects, concentrate on simple mathematics of CI dynamics and speak of determinism. But factually our way of obtaining definite pictures in CM is the same as our way of obtaining an interference pattern in QM. In both cases we take huge ensembles of points. In this sense QM results - wave functions, are as determinate as CM ones, if dealt with properly - describing ensembles of points and thir derivatives (average ="position", dispersion ="size", etc.). Unfortunately, in QM (a low intensity regime) we concentrate too much on one-point experimental issue and "discover" "indeterminism" in its prediction. But observing the Moon with one- or few-photon picture brings the same indeterminism in CM as that in QM. So there is only one indeterminism in both CM and QM and it is of the same nature - lack of statistics (lack of data). The randomness of particular points is easily understood as due to "multi-particle", compound, complex nature of observed objects.

 

[Phrak]

Clearly, quantum mechanics, as a set of axioms that includes the Born postulate,

P(x) = ∫ |Ψ(x,t)|² dx, where P(x) is a probability density,

is a nondeterministic system.

 

[Fredrik]

I can safely say that nobody understands Classical Mechanics. I mean where CM determinism comes from.

I think it comes from the fact that the contribution from non-renormalizable terms in QFTs are negligible at low energies. (The proof is an order-of-magnitude estimate based on dimensional analysis of the coupling constants. I read about it 11 years ago and I didn't fully understand it). For example, if we view QED as an effective field theory it should contain all the interaction terms that are consistent with Lorentz invariance and U(1) gauge invariance, but all but one are non-renormalizable and therefore negligible at low energies. The classical limit of the renormalizable theory is classical electrodynamics, which is nice enough to ensure that Newton's second law (for forces caused by electrodynamic interactions) is a differential equation of the form

$$\vec x''(t)=f(t,\vec x(t),\vec x'(t))$$

where f is just a polynomial. The determinism in CM comes from the fact that such equations have exactly one solution for each initial condition.

 

[Fredrik]

Clearly, quantum mechanics, as a set of axioms that includes the Born postulate,

P(x) = ∫ |Ψ(x,t)|² dx, where P(x) is a probability density,

is a nondeterministic system.

If we assume that the mathematical model defined by the axioms is a description of what actually happens when experiments are performed (the many-worlds interpretation), it can only be described as completely determininstic.

If we instead assume that the mathematical model defined by the axioms doesn't describe what actually happens (the ensemble interpretation), the time evolution of the state vector is still deterministic, but measurement results are not.

 

[Winter Flower]

my approach during the courses was to adapt the best possible survival view - the copenhagen view, where the arbitrary choices was to be treated as "facts of science". This was just a survival strategy, otherwise I would have spend all time questioning the formalism, instead of learning how to use it (which is after all the purpose of the course).

This is like the tragedy of my undergrad physics experience. I would like to understand where the formalism comes from every step of the way. I'm assuming one gets to see more of that in grad school, but I won't be able to if I can't pass my QM class, and I think that once a grad student I would not care so much/be more concerned with other problems...

 

[Phrak]

If we assume that the mathematical model defined by the axioms is a description of what actually happens when experiments are performed (the many-worlds interpretation), it can only be described as completely determininstic.

If we instead assume that the mathematical model defined by the axioms doesn't describe what actually happens (the ensemble interpretation), the time evolution of the state vector is still deterministic, but measurement results are not.

That's an awfully good point. The abstract formalism may be nondeterministic, but if the nondeterministic parts describe an incomplete, subjective measurment, the physical reality can still be deterministic. And Mwi fits this description nicely...

Do you know how either the pilot wave interpretation or ensemble interpetation interprets the Born postulate?

 

[Neo_Anderson]

Proof that the theoretical community is not happy with quantum mechanics: In Aspect's Experiment, physicists looked for all kinds of 'loopholes' to find out why Alain Aspect's experiment worked. THIS HAS BEEN THE ONLY INSTANCE IN THE HISTORY OF PHYSICS WHERE THE PHYSICIST SET OUT TO LOOK FOR FLAWS IN AN EXPERIMENT THAT VERIFIED THE THEORETICAL RESULT!
Only abject doubt of the theory can inspire the physicist to do this.

 

[Neo_Anderson]

It is not really what I wanted to underline. In CM we can entirely stay within CM to see where CM determinism comes from. It's easy.

Let us consider a body that is cinsidered as a point in CM. In fact, it is not a just point but a compound system. In its "entire" CM descriprion we naturally use the center of inertia (CI) or center of mass coordinates R(t) and the relative coordinates {r_i}, i = 1-N, N>>1. The relative coordinates are normally oscillating/rotating and exchanging their energy with the envoronement. For example, we see the full Moon due to light emitted with the Moon's internal degrees of freedom. We take many-photon picture, make an average of it and obtain one definite value R(t). The entire concept of space-time in CM implies this multi-photon exchange. Then we forget about the way how we "observe" CM objects, concentrate on simple mathematics of CI dynamics and speak of determinism. But factually our way of obtaining definite pictures in CM is the same as our way of obtaining an interference pattern in QM. In both cases we take huge ensembles of points. In this sense QM results - wave functions, are as determinate as CM ones, if dealt with properly - describing ensembles of points and thir derivatives (average ="position", dispersion ="size", etc.). Unfortunately, in QM (a low intensity regime) we concentrate too much on one-point experimental issue and "discover" "indeterminism" in its prediction. But observing the Moon with one- or few-photon picture brings the same indeterminism in CM as that in QM. So there is only one indeterminism in both CM and QM and it is of the same nature - lack of statistics (lack of data). The randomness of particular points is easily understood as due to "multi-particle", compound, complex nature of observed objects.

This post makes some very convincing points. But where CM suceeds is when CM goes beyond the need of a set of data (only one set of data is needed to describe the angular momentum of a liquid vortex; none more are needed to provide the basis for the next theory on fluid flow dynamics). QM, on the other hand, has to acquire a set of data for just about every theory or hypothesis that is set fourth. This is due to QM's statistical nature.
Saying that Pauli's Matrices are comprehensive as they stand is not enough.

 

[Neo_Anderson]

Do you know how either the pilot wave interpretation or ensemble interpetation interprets the Born postulate?

I don't, but I'm willing to bet that both interpretations fit in equally well with the Born Postulate.
Am I right?

 

[alxm]

An explination of the problem: Suppose, after Maxwell developed his Law of the Constancy of the Speed of Light (in vacuo), the only way Physicists could reconcile this Law was with the Aether 'theory.' Suppose further that this 'theory' continued unabated, without an Einstein to reconcile Maxwell's Law. The Michleson/Morley experiment is explained away with a modified version of the Aether called the ohr/Sommerfeld Model, in which the Aether moves with the x and y coordinate frames.
There. Aether does not violate the M/M experiment!

Maxwell never claimed the speed of light was constant in different inertial frames.
The Bohr-Sommerfeld Model is a model of the atom, and has nothing whatsoever to do with either the ether or special relativity.

I'd like to point out the forum rules on this kind of stuff. If you want to ressurrect the aether or whatever, you'll have to take it somewhere else.

 

[Fredrik]

Proof that the theoretical community is not happy with quantum mechanics: In Aspect's Experiment, physicists looked for all kinds of 'loopholes' to find out why Alain Aspect's experiment worked. THIS HAS BEEN THE ONLY INSTANCE IN THE HISTORY OF PHYSICS WHERE THE PHYSICIST SET OUT TO LOOK FOR FLAWS IN AN EXPERIMENT THAT VERIFIED THE THEORETICAL RESULT!
Only abject doubt of the theory can inspire the physicist to do this.

Sorry, but this is nonsense. Physicists always look for loopholes, and Aspect got the result that almost everyone expected, so it's not like everyone felt that they needed to "figure out what he did wrong".

 

[Neo_Anderson]

Maxwell never claimed the speed of light was constant in different inertial frames.
The Bohr-Sommerfeld Model is a model of the atom, and has nothing whatsoever to do with either the ether or special relativity.

I'd like to point out the forum rules on this kind of stuff. If you want to ressurrect the aether or whatever, you'll have to take it somewhere else.

I was trying my best metaphor on the issue, alxm. The metaphor was the aether and special relativity, and their relationship to the current state of quantum mechanics, that's all.
Everyone knows the sommerfeld model is the old quantum physics, just as everyone knows Shrodinger and Heisenberg are credited with the new quantum physics. To ilustrate the metaphor, I used Sommerfeld and Schrodinger to give the reader a clear intent of the purpose of my metaphor. And the purpose of my metaphor is just this: that the current state of QM may rest on an "incomplete or unsatasfactory theory" (Einstein), just as my metaphor tried to illustrate QM as being incomplete, just as the aether was.

Now would you please point out the forum rule I violated. You said you would...

 

[Fredrik]

Do you know how either the pilot wave interpretation or ensemble interpetation interprets the Born postulate?

I don't know the Bohm stuff well enough to answer that part of the question, but the ensemble interpretation is very clear on this. The Born rule should be interpreted as nothing more than what it's actually saying. It's part of a set of rules that you can use to calculate probabilities of possible results of experiments, and doesn't tell you anything at all about what "actually happens".

 

[Fra]

This is like the tragedy of my undergrad physics experience. I would like to understand where the formalism comes from every step of the way.

Such an ambition is hard to maintain all along since some steps ad hoc from a physical point of view, and the defense is that it really works and makes a good model. There simply is not magic explanation that the teachers aren't tell you - they really don't know either.

Until someone comes up with something clever, there are two ways. Either the axiomatic way, or the historical way. I always feel the axiomatic way is somewhat of and artifact, and the historical way actually does provide at least a motivation for for QM was developed.

The axiomatic way, was my preferred way up until QM. But then I realized what was wrong with it: sometimes you have to replace the axioms. Thus the problem can not be axiomatized, since the development of the axiom system itself doens't fit in the same framework.

I soon realized that some of these answer I need to find on my own, there is no plain course you take to sort this out. The more advanced courses BUILDS onto this, rather than reconstructs it. But the time to do that seriously, I think isn't in the middle of a regular course even though I think it's good to have a critical mind.

/Fredrik