# I What's wrong with Quantum Mechanics and its teaching?

1. Apr 14, 2017

### MichPod

I am afraid I have no enough competence to raise this topic. I should not have. Because of a very limited experience I cannot back up my arguments. Because of knowing mostly my own experience I should have not made generalizations. Because of not reading completely even one textbook of QM, I should be silent.

And yet I am quite interested in this topic, so let me try to bring some points as I see them, may be with some polemical exagerrations.

1. Nobody understands QM, as Feinman said.
2. Most of the QM textbooks are not willing to talk about this situation, pretending instead they give some "logical" and "reasonable" explanations for the things which are actually controversial and not solved.
3. Textbooks are full of obsolete stuff like "wave-particle duality", half-classical way of analyzing uncertainty principle etc.
4. No textbook is willing to say that nobody knows what "measurement" is and no textbook says that having "Born rule" as a separate postulate is problematic for a respectful theory, to say the least. Well, some may try to explain that there are problems in QM in some last chapter, after already attempting to indoctrinate the reader through the whole book into belief that QM is just "regular" "normal" "nice" theory which student is supposed to understand and accept the same way as he understands and accepts other physical topics.
5. Books are written in a wrong way, scientists are lying (or used to lie through most of the XX century) pretending there are generally no problems in QM and saying that to the general public, to the undergraduate students and to each other.

Why is all this? Why QM topics could not be discussed fairly? Why do we have bad textbooks? Are we so dogmatic, so willing to conceal our incompetence and pretend we are all knowing, have we not yet departed from teaching the science as a religion which should be believed in? Are we after all afraid to say to ourselves and others that there are things we do not understand and our best theories are problematic and a bit ugly?

Thoughts?

Disclaimer: please don't tell me that QM makes right predictions, that it works and that it is the best theory we have and the best theory ever created by the humanity. I know that. And I will agree. )))

Last edited: Apr 14, 2017
2. Apr 14, 2017

### Demystifier

Well, some QM textbooks do discuss the controversial interpretation aspects. One of them is the Weinberg's.

3. Apr 14, 2017

### vanhees71

Well, there are many good textbooks, among them Sakurai's, Ballentine's, and Weinberg's. Why there are so many textbooks still mention wave-particle duality, which is indeed obsolete for more than 90 years now, is an enigma to me too. To claim that nobody understands what a measurement is, is somehow contradicting experience since our experimental colleagues do measurements all the time. Particularly they are doing measurements concerning the quantum nature of phenomena that are really amazing in their precision and ingenuity. These people for sure understand what a measurement is since otherwise they couldn't do all these marvellous experiments testing QT to the extreme.

From the theoretical side, I don't see, why Born's postulate should be problematic in any way. It's confirmed by all these experiments, and QT is an accurate description of everything what's observed so far. So why should any textbook mention that it is problematic, if it isn't?

What's of course great is to think about in how far any of the postulates of standard QT is dependent on the others or maybe can be derived from the others. An example is the thorough treatment of the question whether Born's postulate can be derived from the other postulates in Weinberg's textbook. The conclusion is that it seems not to be derivable from the other postulates. Only the conclusion, that, as Weinberg says, the interpretation problem is still open, I cannot follow. There is an interpretation all physicists follow, and that's the minimal interpretation. It's the application of the highly abstract formalism of QT to real experiments and observations that works with an astonishing precision.

That this may not satisfay anybody's worldview is not a problem of physics but of philosophy or even religion. Nature doesn't care about our feelings but just is the way it is, and it seems to be pretty accurately described by QT. As any theory of physics it might be disproven by some observation in the future, and then hopefully one discovers an even better theory to desribe the world. That's the aim of science but not to solve pseudo-problems of a philosophical nature. It's nice for the philosophers to have these problems, so that they can write books, but it's irrelevant for natural science!

4. Apr 14, 2017

### ftr

Because it is inherently a human endeavor.

After living many decades and being exposed to many fields engineering, business, medicine...etc. You will always be dealing with very well known facts/knowledge, and the so so and the extreme confusion at the other end of the spectrum. Add to all that individuals perceived knowledge of the said status.

I also think that if you really are interested you should read the older (original) textbook, papers and the history books like "QED and the men who made it" to get a good perspective on how physics is produced.

here is a link to some of the original papers
http://web.ihep.su/dbserv/compas/src/

Last edited: Apr 14, 2017
5. Apr 14, 2017

### stevendaryl

Staff Emeritus
@MichPod:

@vanhees71: (paraphrasing slightly)

6. Apr 14, 2017

### kith

I don't agree with many of the premises of the OP: that there's something "unsolved" about QM, that everybody agrees on what it is and that textbook authors and scientists lie about it.

All attempts to state what's "unsolved" about QM I have seen, made assumptions which I think Bohr and the old Copenhagenists would have rejected. For me, it is interesting to pinpoint exactly what bugs me and other people about QM, but given my knowledge of QM, I am skeptical that these questions really have answers.

I do think that the presentation in many textbooks could be improved by contrasting the concepts of QM with classical mechanics, by reflecting upon the term "measurement" and by showing what happens if we try to model the measurement apparatus from within QM. But I don't think textbook authors leave these things out to deceive the readers. For a textbook which has the goal to make physics students get familiar with how QM works, it seems reasonable enough to not want to talk about speculative, subjective and controversial topics as well as about more technical aspects.

Last edited: Apr 14, 2017
7. Apr 14, 2017

### atyy

In fact all (good) attempts to state what is unsolved agree fundamentally with Bohr and the old Copenhagenists: quantum mechanics needs a classical/quantum cut and there is no quantum reality.

The disagreement, found even among the old Copenhagenists, is whether this is a bug or a feature, or both!

But at the fundamental level, there is consensus.

Last edited: Apr 14, 2017
8. Apr 14, 2017

### Swamp Thing

9. Apr 14, 2017

### kith

For me, that's an odd way to put it. By "quantum mechanics" you seem to refer to the textbook recipe of orthodox QM which essentially is a less philosophical version of Copenhagen. So sure: people who think that something about orthodox QM needs to be solved should agree about what it actually says.

What I wanted to say with the paragraph you quoted is that no matter what people think needs to be solved, Bohr disagrees because Bohr is happy with Copenhagen.

Last edited: Apr 14, 2017
10. Apr 14, 2017

### atyy

Well, as I wrote above:

"The disagreement, found even among the old Copenhagenists, is whether this is a bug or a feature, or both!

But at the fundamental level, there is consensus."

11. Apr 14, 2017

### kith

I don't get it. This thread is about why textbooks are written the way they are given that everybody knows that QM has problems. I pointed out that influencial people like Bohr didn't think that QM has problems so maybe that's why. Your comments are about details (Bohr and other Copenhagenists disagreed about things) and something unrelated (what is the correct understanding of QM).

12. Apr 14, 2017

### atyy

Many textbooks don't even discuss Copenhagen correctly. Any textbook discusses Bohr's position, would immediately implicitly point out the problems, even without stating explicitly that it is a problem. So true Copenhagenists of all stripes should agree with the OP: Copenhagen should be taught explicitly and properly.

13. Apr 14, 2017

### Aufbauwerk 2045

I would not place too much attention on the famous Feynman quote about no one understanding QM, or about it being crazy, etc. I have seen one of his lecture series in which he says that sort of thing, but he also said maybe it's because he is older and some of the ideas take getting used to, but the younger generation will have no misgivings. He said in any case that's the way nature works, whether we think it's crazy or not, and if you don't like it, that's too bad, because that's the way it is.

On the other hand, he said that QED is the most successful physics theory of all time, and talked about how measurements agree with theory up to an amazing number of decimal places. He was rightly proud of this because he was one of the main people in developing QED.

Actually physics and other hard sciences do make sense, which you understand when you become familiar with them. In fact, in a world gone mad, you may find that mathematics, physics, and other STEM fields are about the only thing that does make sense.

:)

14. Apr 15, 2017

### Staff: Mentor

If we can't tell you that, we can't answer your question. When textbooks talk about the right predictions, and omit or gloss over the things your OP says they should be talking about, it's because the right predictions are what's important. There is no rule that says that science has to conform to any of our preconceived notions about what it "ought" to explain. The only rule is that science has to make right predictions. So that's what the textbooks focus on: the models that make the right predictions.

15. Apr 15, 2017

### vanhees71

No, there's no consensus. I don't believe you need a cut. It's all describable with QT. The validity of the classical approximation for macroscopic systems in almost all situations is due to coarse graining and derivable from many-body theory. It's more or less what solid-state physics is about.

16. Apr 15, 2017

### rubi

I don't think there is anything problematic with QM that needs to be fixed. Of course, it sometimes goes against our intuition, but that just means that our intuition is wrong. In order to understand, what might be problematic about QM, we first need to pinpoint what the difference between QM and classical theories is. In this post, I have explained that the only difference is that the probability distributions $P_O$ associated to the quantum observables $\hat O$ don't derive from a big probability distribution. This might seem strange, but we really deal with the same situation every day. For example, we know a probability distribution for the IQ distribution of humans and we know another probability distribution for the GDP of all countries. Nobody would require these probability distributions to be derivable from some all encompassing probability distribution of the universe. Yet, nobody believes that a measurement of the GDP of Japan collapses the IQ of Donald Trump (for instance).

17. Apr 15, 2017