# Are physicists happy with Quantum Mechanics as it is?

1. Nov 14, 2009

### 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?

2. Nov 14, 2009

### Redd

I don't think Physicists are ever happy.

But that's just a layman interpretation.

3. Nov 14, 2009

### 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.

4. Nov 14, 2009

### 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.

5. Nov 14, 2009

### 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 wont happen)

6. Nov 14, 2009

### 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...

7. Nov 14, 2009

### ytuab

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

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.

Last edited: Nov 15, 2009
8. Nov 14, 2009

### 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.

9. Nov 15, 2009

### 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.

10. Nov 15, 2009

### Phrak

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.

11. Nov 15, 2009

### lmont

though i wont 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.

12. Nov 15, 2009

### humanino

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

13. Nov 15, 2009

### alxm

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.

14. Nov 15, 2009

### 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.

15. Nov 15, 2009

### Fra

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 alot 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

16. Nov 15, 2009

### Fra

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

Last edited: Nov 16, 2009
17. Nov 15, 2009

### 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 alot 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, alot 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

18. Nov 15, 2009

### 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 dialation 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.

Last edited: Nov 16, 2009
19. Nov 16, 2009

### Demystifier

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.

20. Nov 16, 2009

### Bob_for_short

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

21. Nov 16, 2009

### Demystifier

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

22. Nov 16, 2009

### Bob_for_short

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 {ri}, 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.

Last edited: Nov 16, 2009
23. Nov 16, 2009

### 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.

24. Nov 16, 2009

### Fredrik

Staff Emeritus
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.

25. Nov 16, 2009

### Fredrik

Staff Emeritus
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.