Is the Following How Most Students Think of Einstein's View Of QM

[bhobba]

I was over on another forum discussing what Einstein thought of QM - namely he thought QM correct - but incomplete. His viewed changed a bit over time, but that was his final view. Anyway here is the reply I got:

No serious Physicist (including all of my professors) thinks he was right. It's mostly ignorant Einstein cultists who peddle these rumours. Einstein never believed in the underteministic nature of Quantum mechanics and he was dead wrong. Because that's the first thing you need to believe in. Quantum Mechanics so far is the single most perfect theory in physics because it works more or less everywhere. Even relativity hasn't worked in numerous cases but QT works in every scenario. He was totally wrong with his deterministic viewpoint of physics and his ideas regarding QT are no longer discussed in any serious Physics seminar.

That's not the general view on this forum, but I am curious if it's the general view taught in QM courses. I doubt it personally, but I learned QM not at university, but by self teaching. Of course I believe 'Quantum Mechanics so far is the single most perfect theory in physics'. But more or less everywhere? Where exactly does it not work? Maybe Quantum Gravity - but that is something that requires deeper 'discussion'

Thanks
Bill

 

[jedishrfu]

While I learned QM in the 1970's, I don't remember that Einstein was bashed like that. For sure, his spooky action at a distance raised certain doubts in QM and his belief that there may yet be hidden variables that better describe a system was also known.

Nowadays, Bell's theorem has taken sway in QM theory and quantum entanglement is a real thing.

Ethan Siegal published this article about Einstein's mistakes that is interesting reading:

https://www.forbes.com/sites/starts...es-of-einsteins-scientific-life/#3975faa8db42

In general, Einstein is a beloved genius lionized early on, and now there are so many articles on Einstein's mistakes because its sadly human to tear someone else down to size.

"We like our heroes well done and ready to eat."

 

[PeterDonis]

am curious if it's the general view taught in QM courses.

It's been a long time since I took a QM course, but the ones I took didn't waste any time talking about the history of the field or which physicists were "right" or "wrong" about it. They had enough to do just teaching the basics of how to use the theory to make predictions.

 

[bhobba]

and now there are so many articles on Einstein's mistakes because its sadly human to tear someone else down to size.

I really enjoyed the interesting book by Ohanian on Einsteins Mistakes. But his conclusion was Einstein was like a 'sleepwalker' - he knew where he wanted to go but was not always 'perfect' in how he got there. It simply makes him more human, and in no way diminishes his genius. As Feynman, yes the 'magician' Feynman, admitted, knowing only what Einstein did he could not have come up with Relativity. Despite his well known disagreements with Bohr, Bohr never wavered in his opinion that General Relativity was the greatest ever creation of the human mind. Landau simply said - if you are not in awe of GR you are not a physicist (or words to that effect).

Thanks
Bill

 

[PeterDonis]

Where exactly does it not work?

We don't use QM to make predictions about macroscopic phenomena, like the trajectories of baseballs or spacecraft or the motions of the planets. We don't use QM in fluid dynamics on macroscopic scales--for example when modeling airflow over a wing or water flow through a pipe. We don't use QM in modeling the large scale structure of the universe. And so on.

Claims that QM works "everywhere" ignore the above. Such claims are based on the belief that we can derive an appropriate classical limit of QM for all such cases, and therefore using classical (non-quantum) physics in such contexts "counts" as using QM. But first, I'm not sure the classical limit is as straightforward as is often claimed; and second, cases in which General Relativity is involved are problematic because we do not have a good theory of quantum gravity of which GR is the classical limit.

I also have no idea what "even relativity hasn't worked in numerous cases" means. I'm not aware of any case for which relativity does not work, since QFT is consistent with relativity and, unlike the general classical limit of QM, the non-relativistic limit of relativistic QFT is not problematic at all that I'm aware of.

 

[Demystifier]

For those not working in quantum foundations (which is the majority of physicists), standard QM answers all the questions they ask, so in this sense QM is complete for them, and hence Einstein, who argued that QM is incomplete, was wrong. For those working in quantum foundations the opinions are quite splitted, depending on which additional questions they ask.

 

[vanhees71]

Then I'm somewhere in between. QT is incomplete but not in the sense Einstein thought it to be incomplete. A theorie is as long complete as it describes quantitatively correctly all the phenomena it is supposed to describe, and that's indeed the case for modern QT for 95 years now, and the more it is tested the better the agreement between experiment and predictions get. It's incomplete, because there is no satisfactory description of the gravitational interaction within QT yet.

The common narrative that Einstein has not understood QT well enough and thus came to the wrong conclusion about its completeness is also wrong or at least very superficial. Einstein was one of the physicists who understood the subject best. Particularly his clear distinction between apparent nonlocality and inseparability following from entanglement is mostly ignored till today and gives rise to a lot of confusion concerning apparent contradictions between relativistic causality and relativistic QFT, which of course is consistent with relativistic causality by construction.

Somewhat unfortunate is the overemphasis of the EPR paper concerning Einstein's view on quantum theory. Einstein himself did not like the paper as it was written by Podolsky and he explicitly said that it does not adequately describes his issues with QT, which was rather inseparability than locality or "realism", which is a word which cannot be used any longer since the EPR paper, because it has no well-defined meaning anymore, because of the obscure formulation in the EPR paper. Bohr's as famous reply obscures the issue even more than helping to clarify it. Finally also philosophers took over the "foundations issues" and made it completely incomprehensible too. That's why for a long time the foundation questions have had a bad reputation and where a job killer for any young physicist.

This has been overcome only thanks to Bell's seminal work, who ingeniously discovered a physical formulation of the separability question (or for Einstein the separability problem), which could been answered empirically, and it was answered quite quickly in the early 80ies by Aspect et al doing corresponding "Bell experiments". The result is well known: QT is the correct description with a statistical significance and accuracy which is very rare in physics. In this sense indeed Einstein's view is refuted with a very high significance, and the inseparability described by entanglement within standard QT must be considered correct.

For me, this issue is closed, and one can concentrate on the real problems with the foundations, i.e., finding a quantum description of gravity rather than hunt some ghosts of the past. The development around the separability issue is now rather at a level of engineering, i.e., the fundamental discoveries can be used for modern technology of the near future, like quantum cryptography and quantum computing.

In this sense these foundational questions have lead to very fruitful scientific and practical results, but as to be expected this is not due to unclear philosophical speculation but the robust scientific method, where real-world experiments decide about theories, which in turn are needed to invent such experiments to begin with.

 

[atyy]

Messiah explicitly says Einstein may have been right. Even Landau and Lifshitz subtly leave the door to Einstein's view open. Weinberg explicitly discusses these problems. All these classic books point to the problem. And they also wisely teach Copenhagen as a practical first step.

 

[256bits]

No serious Physicist (including all of my professors) thinks he was right. It's mostly ignorant Einstein cultists who peddle these rumours. Einstein never believed in the underteministic nature of Quantum mechanics and he was dead wrong. Because that's the first thing you need to believe in. Quantum Mechanics so far is the single most perfect theory in physics

Wow. An open mind!
Would the responder never have guessed asking questions about a theory and its implications is par for the course of the scientific way, regardless of how beautiful it may appear.
Only reason I am typing here is that I consider the prose a little bit over the top.

 

[martinbn]

I don't know about the QM courses, but in the popular literature/films it is presented saying that Bohr won the debate with Einstein. But I personally never took it to mean anything about either of them. To me it meant that QM is ok.

On the other hand, and this is probably off topic, Einstein did prove that QM is incomplete. And I emphasize that he proved it, he didn't just have an opinion. Here incomplete is understood as Einstein defined it. One can disagree with the definition and think that it is not a useful one, but according to it QM is incomplete. I personally don't see why a given theory should be complete, why it is a problem that it is incomplete. After all nature doesn't care about humans philosophical comfort. And if I am allowed one more off topic comment. Bell proved that any completion of QM has to be non-local in some sense. Some people take it to mean that nature is non-local(!). I think it means that QM is incomplete and it cannot be completed.

 

[vanhees71]

Can you give a reference for this "proof of incompleteness"? I've never heard about such a proof before. For sure the violation of Bell's inequality and it's overwhelming empirical verification doesn't say anything about completeness or incompleteness of QT. It just says that local deterministic hidden-variable theories are incompatible with the probabilistic predictions of QT, i.e., Einstein's idea for the solution of his problem (of inseparability) with QT violates overwhelming empirical evidence.

 

[martinbn]

Can you give a reference for this "proof of incompleteness"? I've never heard about such a proof before. For sure the violation of Bell's inequality and it's overwhelming empirical verification doesn't say anything about completeness or incompleteness of QT. It just says that local deterministic hidden-variable theories are incompatible with the probabilistic predictions of QT, i.e., Einstein's idea for the solution of his problem (of inseparability) with QT violates overwhelming empirical evidence.

I said incompleteness in the sense Einstein used it in the EPR paper i.e. the theory needs to account for all elements of reality i.e. for anything that can be predicted with 100% certainty. You are probably thinking of something else.

 

[vanhees71]

There is no reality in the sense of the EPR paper, but everything, including the randomness of measurement outcomes even for completely determined pure states, is according to the observations, and that's why the probabilistic predictions of QT describe the "reality", i.e., everything that's objectively observable, better than any local deterministic theory. The reality criterion of EPR is thus itself unrealistic ;-).

 

[PeterDonis]

incompleteness in the sense Einstein used it in the EPR paper i.e. the theory needs to account for all elements of reality i.e. for anything that can be predicted with 100% certainty.

I'm confused. What do you think the EPR paper proved?

 

[vanhees71]

I'm confused for decades concerning what the EPR paper might have proven. I can't tell! For me it's just an example for the old logical rule "ex falso quodlibet".

 

[Nugatory]

On the other hand, and this is probably off topic, Einstein did prove that QM is incomplete.

It might be better It's to say that the EPR shows that either: 1) QM is incomplete or; 2) Our classical intuition about how everything works is wrong. When I read the EPR paper, it seems clear to me that the authors were aware of the #2 possibility but did not accept it - a very reasonable position to take at the time.

To me, one of the most tantalizing "what if" questions is: What if Einstein had lived long enough to see Bell's theorem?

 

[vanhees71]

Indeed, but I'm pretty sure, he'd have accepted that his idea about local hidden variable theories don't work. Then he'd realized that then to save determinism he'd have to accept nonlocal theories. Maybe he would have just moved on looking for a classical non-local generalized field theory...

 

[Nugatory]

Maybe he would...

And maybe not... That's what makes the speculation so much fun.

 

[vanhees71]

Sure, it's pure speculation.

 

[Lord Jestocost]

....discussing what Einstein thought of QM - namely he thought QM correct - but incomplete.
....No serious Physicist (including all of my professors) thinks he was right.

Einstein wrote in a letter to Schrödinger in 1939 (Albert Einstein, Letters on Wave Mechanics: Correspondence with H. A. Lorentz, Max Planck, and Erwin Schrödinger):

“Dear Schrödinger,

. . . . . . .

Now to physics. I am as convinced as ever that the wave representation of matter is an incomplete representation of the state of affairs, no matter how practically useful it has proved itself to be. The prettiest way to show this is by your example with the cat (radioactive decay with an explosion coupled to it.) At a fixed time parts of the ψ-function correspond to the cat being alive and other parts to the cat being pulverized.

If one attempts to interpret the ψ-function as a complete description of a state, independent of whether or not it is observed, then this means that at the time in question the cat is neither alive nor pulverized. But one or the other situation would be realized by making an observation.

If one rejects this interpretation then one must assume that the ψ-function does not express the real situation but rather that it expresses the contents of our knowledge of the situation. This is Born’s interpretation which most theorists today probably share. But then the laws of nature that one can formulate do not apply to the change with time of something that exists, but rather to the time variation of the content of our legitimate expectations.

Both points of view are logically unobjectionable; but I cannot believe that either of these viewpoints will finally be established.

There is also the mystic, who forbids, as being unscientific, an inquiry about something that exists independently of whether or not it is observed, i.e. the question as to whether or not the cat is alive at a particular instant before an observation is made (Bohr). Then both interpretations fuse into a gentle fog, in which I feel no better than I do in either of the previously mentioned interpretations, which do take a position with respect to the concept of reality.

I am as convinced as ever that this most remarkable situation has come about because we have not yet achieved a complete description of the actual state of affairs.

Of course I admit that such a complete description would not be observable in its entirety in the individual case, but from a rational point of view one also could not require this.

I write this to you, not with any illusions that I will convince you, but with the sole intention of letting you understand my point of view, which has driven me into deep solitude. I have also brought it to the point of a real mathematical theory, whose testing, however, is naturally very difficult.

Best regards from

Yours,

A. Einstein"

EDIT: Einstein was a man of character and strong opinion. Is it "not right" when somebody is looking for the "ulimate reality" behind what we call "perceptions"?

 

[RUTA]

I attended undergrad and grad programs in physics using ”quarters” — three terms to an academic year (summer term makes 4). Anyway, undergrad and grad combined I took 11 quarters of QM (not counting the courses in QFT, particle physics, and string theory) from Park, Tipler, Shankar, a text in solid state physics, and a text in nuclear physics. I took these courses 1981 — 1985. Not one mention of entanglement, nonlocality, the EPR paradox, the Bell inequality, or interpretations of QM. We just solved physics problems.

 

[vanhees71]

Well, I guess that was too early to have Bell in the standard lectures. When was Aspects success again? I'm pretty sure it's in the early 80ies so just about the time you took your QM course.

Mine was in the early 90ies (my QM course lectures must have been around 1993-1994) and though our professor was close to his retirement he was full of enthusiasm to teach the modern aspects of QT, particularly also about Bell's inequality and its violation in QT.

I think that indeed the negative attitude against "foundations of QT" was overcome just due to the fact that (a) Bell made a scientific breakthrough, bringing it from the realm of unsharp philosophical gibberish with little significance for (even most fundamental) physics to a real physics question and then the experimental breakthrough by Aspect et al who proved that the question was indeed feasible with real-lab experiments.

Another aspect might be the general cultural changes in the late 60ies and early 70ies, as is reflected in the title of Kaiser's very nice science-historical book "How the hippies saved phycis" ;-)).

 

[EPR]

We cannot dismiss by simple handwaving that our brains evolved to observe and make sense of the macro world. It is possible that the particular brain wiring evolved and adapted to the specific conditions present only at the macro scale. What we see as quantum rules are not hardwired in our brains and hence seem incomprehensible(fundamental uncertainty, nonlocality, non realism, etc.). It is possible that Nature does not care that our intuition fails at scales we were never designed to probe with our causally deterministic evolutionary way of thinking. This may never go away even if we discover the hypothetical master equation(TOE).
I have sympathy with the instrumentalists as the conceptual issue may be much deeper than it seems and may even be insolvable.

What does 'making sense of something' really mean?

 

[physika]

Claims that QM works "everywhere" ignore the above. Such claims are based on the belief

Right.

Beliefs, just that...

.

 

[bhobba]

Wow. An open mind!.

Of course. He responded and admitted he was a college student. I linked him to a few papers, as well as asking him to take a look at Ballentine, and the Ensemble interpretation it has integrated throughout the text was the interpretation Einstein held to. He calmed down somewhat and I explained whenever he hears things with such 'certainly' best to come here and get a more balanced view. It just struck me as the exact opposite how people should be thinking about QM, especially early on. A bit more 'humility' is needed. It's fine to hold a particular view, and strongly adhere to it, but still be at least a bit open.

Also we discussed it's importance and agreed for doing QM it's not of much value, and that is what he should be concentrating on to start with. Leave it to a course on the history and/or interpretations of QM some colleges offer.

Of course I never would do that (yea - right - I still wince at some posts I made especially early on).

Thanks
Bill

 

[bhobba]

QT is incomplete but not in the sense Einstein thought it to be incomplete.

That, as is well known, is my view as well, and I carefully explained it to him eg quantum gravity. As I mentioned in another post when he responded and had calmed down he was more receptive to a more 'subtle' view on the matter. But is best left to a course that concentrates on such things - learn the formalism first.

Thanks
Bill

 

[bhobba]

Messiah explicitly says Einstein may have been right. Even Landau and Lifshitz subtly leave the door to Einstein's view open. Weinberg explicitly discusses these problems. All these classic books point to the problem. And they also wisely teach Copenhagen as a practical first step.

Yes - I did mention such 'certainty' is not in the scientific spirit.

Thanks
Bill

 

[bhobba]

Einstein was a man of character and strong opinion. Is it "not right" when somebody is looking for the "ulimate reality" behind what we call "perceptions"?

Of course.

Thanks
Bill

 

[bhobba]

Well, I guess that was too early to have Bell in the standard lectures.

I first became interested in QM just after finishing my degree and reading In Search of Schrodinger's Cat by John Gribbon. He suggested if you want the detail studying Dirac's Principles of QM and Von-Neumann's Mathematical Foundations. Bad move. Von-Neumann was a breeze - it simply was an extension of Hilbert's spaces I had done as one of my subjects - but Dirac was another matter - especially after Von-Neumann's scathing attack on his math. I originally sided with Von-Neumann and thought Dirac mathematically dubious - how wrong I was - but that took a few years to dawn on me. BTW to newbies do not learn QM from either of those books - get them later for your reference library - Gribben was wrong - other books are MUCH better to start with. Anyway Gribben discussed Bell at length but no detail in Von-Neumann or Dirac.

Thanks
Bill

 

[Demystifier]

QT is incomplete but not in the sense Einstein thought it to be incomplete. A theorie is as long complete as it describes quantitatively correctly

There is a conjecture (asymptotic safety http://www.percacci.it/roberto/physics/as/faq.html) that quantized Einstein-Hilbert action is renormalizable in a non-perturbative sense. If someone proved that conjecture, would you then say that QT is complete?

 

[vanhees71]

I first became interested in QM just after finishing my degree and reading In Search of Schrodinger's Cat by John Gribbon. He suggested if you want the detail studying Dirac's Principles of QM and Von-Neumann's Mathematical Foundations. Bad move. Von-Neumann was a breeze - it simply was an extension of Hilbert's spaces I had done as one of my subjects - but Dirac was another matter - especially after Von-Neumann's scathing attack on his math. I originally sided with Von-Neumann and thought Dirac mathematically dubious - how wrong I was - but that took a few years to dawn on me. BTW to newbies do not learn QM from either of those books - get them later for your reference library - Gribben was wrong - other books are MUCH better to start with. Anyway Gribben discussed Bell at length but no detail in Von-Neumann or Dirac.

Thanks
Bill

It's a bit ironic. Of course von Neumann gave the first mathematical strict formulation of QT within then standard Hilbert-space theory. Dirac's physicist's approach to what is today called distributions of course was irresistable for mathematicians to make rigorous, because it worked so well. The $\delta$ distribution was, however, not first invented by Dirac but already earlier by Sommerfeld in some paper about electrodynamics. I don't go into the physical part of von Neumann's book, which I'd not recommend to study at all ;-).

 

[vanhees71]

There is a conjecture (asymptotic safety http://www.percacci.it/roberto/physics/as/faq.html) that quantized Einstein-Hilbert action is renormalizable in a non-perturbative sense. If someone proved that conjecture, would you then say that QT is complete?

Yes, when there is a working quantum theory of gravitation in accordance with all observables, I'd say there's no incompleteness left.

 

[Demystifier]

Yes, when there is a working quantum theory of gravitation in accordance with all observables, I'd say there's no incompleteness left.

But what if there are two different renormalizable theories of quantum gravity, both of which are consistent with currently existing experimental data? The two theories may have different predictions at very high energies, but with current technologies such high energies cannot be achieved in the laboratories. It that was the case, would you say that QT is complete today?

 

[vanhees71]

Then it's of coarse a question, which of the two theories is correct (or maybe whether neither of them is correct), which has to be decided somehow by experiment (maybe astronomical observations). I think one of the reasons, why there's no satisfactory quantum theory of gravitation, is that there are no observations of "quantum-gravity effects". All observed about gravity is well-described with classical GR, because gravitational interactions play only a major role for macroscopic objects, and so far classical GR (usually tested in the PPN formalism as far as binary systems are concerned, which provide the most accurate tests of GR, including pulsar timing as well as the LIGO/VIRGO measurements of gravitational waves from BH-BH, BH-NS, and (maybe) BH-NS mergers).

 

[Elias1960]

I'm confused. What do you think the EPR paper proved?

I'm confused for decades concerning what the EPR paper might have proven. I can't tell!

That from realism (in the quite weak but well-defined variant of the EPR criterion) and Einstein causality it follows that QT is incomplete.