Best textbook or video or device for understanding QM

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  • #1
yasmin1369
As the title says im looking for some book to read and understand this world. I know many people say its impossible and that we can learn it by learning the math bluh bluh.. But i have passed 4 quantum courses and i know the math. I just cant get the touchable concepts ( i dont really know how to use the words right now). Help me guys!
 
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  • #2
atyy
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Do you at least know the traditional interpretation, in which one makes a subjective division of the world into classical and quantum parts, and in which a measurement is when the classical measuring apparatus interacts with the quantum system such that a definite (also called "classical", "macroscopic" or "irreversible") measurement outcome is registered? The traditional interpretation needs this so-called Heisenberg cut, because there is unitary deterministic time-evolution between measurements and random non-unitary time-evolution called collapse or state reductiuon when a measurement is made, so something outside stating the initial quantum state is needed in order to say which time-evolution rule is used when.
 
  • #3
yasmin1369
I do know that. I know these stuff otherwise i wouldnt have been able to pass those courses. I just want a visual aid. You know when i talk about momentum (classical) i can tell you about the different momentums a truck and a normal car have and you would understand me because you have seen those and felt em. For QM, we cant do that. We cant feel how small an electron is, we only know a number for that. I want a book that can show me how to feel these.
 
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  • #4
atyy
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For visual aids, you can treat the electron as a wave (ie. treat the wave function as real, and treat collapse as real), and use your intuition about waves. Of course, this is just a visual aid, since in the orthodox interpretation, the wave function is just a tool.

For a deeper understanding about what reality may be behind the wave function and the classical world, one needs something like Bohmian Mechanics or Many-Worlds.
 
  • #5
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I do know that. I know these stuff otherwise i wouldnt have been able to pass those courses. I just want a visual aid. You know when i talk about momentum (classical) i can tell you about the different momentums a truck and a normal car have and you would understand me because you have seen those and felt em. For QM, we cant do that. We cant feel how small an electron is, we only know a number for that. I want a book that can show me how to feel these.
You definitely need a book on Bohmian mechanics. I recommend:
https://www.amazon.com/dp/0521485436/?tag=pfamazon01-20&tag=pfamazon01-20
 
  • #6
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A book that places particularly strong emphasis on a physical intuition for the concepts of QM is "Quantum Theory" by David Bohm.
He wrote it before developing Bohmian mechanics so you will find the orthodox-interpretation point of view in it.
 
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  • #7
vanhees71
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You definitely need a book on Bohmian mechanics. I recommend:
https://www.amazon.com/dp/0521485436/?tag=pfamazon01-20&tag=pfamazon01-20
What the heck should this be good for, particularly for the purpose of getting an intuitive understanding of quantum theory? The Bohmian trajectories are nothing real, being unobservable!

I think, the only way to get some understanding of "what's going on in Nature" concerning quantum theory is to look in some detail to various applications of the theory to real experiments. However, one should keep in mind that the goal of physics is not to get some "explanation" about why nature is as it is but to get a precise description of what's going on in nature by identifying as simple a set of "natural laws". This insight can only be gained by a close connection between experiment and theory, and the one and only way to express the theories leading to this type of understanding is indeed math, and the understanding becomes more and more abstract the more you leave the realm of everyday experience which is governed by the laws of classical physics (in our everyday life we are dealing with phenomena which are very well described by classical mechanics of solid bodies and fluids as well as classical electromagnetism, so that some relativity is also involved, but not in a very obvious way).

Quantum phenomena are, on the other hand, present too. If you know that the atoms making up the matter around us are bound systems of atomic nuclei and many-electron systems, the very fact that there is stable matter at all, making the classical effective description sensible to begin with, is a generic quantum phenomenon. At least nobody has ever found any classical explanation for the seemingly obvious fact.
 
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  • #8
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What the heck should this be good for, particularly for the purpose of getting an intuitive understanding of quantum theory? The Bohmian trajectories are nothing real, being unobservable!
Just because something is unobservable does not mean it is not intuitive. For example, I am sure you will agree that Feynman diagrams are intuitive but not observable. Perhaps you will say that Feynman diagrams are a tool which can be used to calculate something observable, but Bohmian trajectories can also be used as a tool to calculate something observable.

Finally, you can say that Bohmian trajectories are not intuitive to you, while Feynman diagrams are intuitive to you. That's fine, different people find different things intuitive. I do not recommend Bohmian mechanics to everybody. But I think I have a lot of experience on different views of QM that different people may have, and I think I can recognize who might like which interpretation. (Test me: Have I been right that you find Feynman diagrams intuitive, even though they are not observable?) From the words of Yasmin I've got a strong impression that Bohmian mechanics would satisfy him.
 
  • #9
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However, one should keep in mind that the goal of physics is not to get some "explanation" about why nature is as it is but to get a precise description of what's going on in nature by identifying as simple a set of "natural laws".
As I stressed many times, the goal of physics is determined by physicists, and not all physicists agree that one of the goals of physics is not to get some "explanation" about why nature is as it is. In particular, I am convinced that Yasmin would not agree with that. Einstein also did not agree with that. John Bell, the discoverer of the Bell inequalities, also did not agree with that. Do you want more examples?

But there is also another "extreme" in the spectrum of the goals of physics. You probably feel proud that your goal of physics (of identifying as simple a set of "natural laws") is much more concrete than that of those who seek "explanation". But you forget that there are also applied physicists (to whom you may be jealous because they get much more money for research than you do) who will say that the goal of physics is not to identify the natural laws, but to apply them to something useful. Compared to you and me, they are concrete and we are not. The way you think about the "explanation seekers" does not differ much from how applied physicists think about you and me.
 
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  • #10
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Yasmin1369: you might reasonably conclude from the last two or three posts that there's more than one way to come an understanding of QM, and that works for one person doesn't necessarily work for another.

You'd be right.
 
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  • #11
yasmin1369
Thanx guys! I will try bohmian mechanics, and btw i am a girl :)
 
  • #12
atyy
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As I stressed many times, the goal of physics is determined by physicists, and not all physicists agree that one of the goals of physics is not to get some "explanation" about why nature is as it is. In particular, I am convinced that Yasmin would not agree with that. Einstein also did not agree with that. John Bell, the discoverer of the Bell inequalities, also did not agree with that. Do you want more examples?
To add more examples, even the masters of-shut-up-and-calculate were very aware of the measurement problem. Landau and Lifshitz mention in passing that the need for a Heisenberg cut is strange, which if one understands the style of their wonderful books, is saying a lot. Dirac mentions the problem in his Scientific American article, and says it will probably have to be solved by a theory beyond quantum mechanics. Even though von Neumann's proof of the impossibility of hidden variables was wrong, he obviously thought about the problem, and till this day his analysis of the measurement process is a good way to show the measurement problem. Weinberg discusses the problem in his quantum mechanics text. Here are more discussions of the problem.

Bell, Against 'measurement' http://www.tau.ac.il/~quantum/Vaidman/IQM/BellAM.pdf

Tsirelson, This non-axiomatizable quantum theory http://cds.cern.ch/record/260158/files/P00021853.pdf

Laloë, Do we really understand quantum mechanics http://arxiv.org/abs/quant-ph/0209123

Wallace, The Quantum Measurement Problem: State of Play http://arxiv.org/abs/0712.0149

For Bohmian Mechanics, some free articles are
Passon http://arxiv.org/abs/quant-ph/0611032
Oriols and Mompart http://arxiv.org/abs/1206.1084
 
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  • #13
Screw textbooks. Either watch the lectures by Leonard Susskind. Or look for pdfs on Google, search for something like "Introduction to QM" pdf or similar words.
 
  • #14
martinbn
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Screw textbooks. Either watch the lectures by Leonard Susskind. Or look for pdfs on Google, search for something like "Introduction to QM" pdf or similar words.
Oh, no! Don't watch Susskind's lectures. It seems that in these lectures (not just quantum mechanics all of them) he talks a lot without actually saying much.
 
  • #15
Oh, no! Don't watch Susskind's lectures. It seems that in these lectures (not just quantum mechanics all of them) he talks a lot without actually saying much.
And this is why?
 
  • #16
BTW: Ok one book that I think is very straight forward is Paul Dirac's Book The Principles of Quantum Mechnics ! It's short and good in coordinate free notation, he even introduces a bit of quantum field theory, but it is a little outdated on that, but that doesn't do much to the whole book. And my general advise would be to read old original literature from the people who came up with the stuff. It's always much more down to earth and not compress to minimum notation and at the same time generalized to the most general case which obscures anything. You find the links to the pdfs on Wikipedia (on a specific topic) most of the time.
 
  • #17
atyy
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The way you think about the "explanation seekers" does not differ much from how applied physicists think about you and me.
Hey, hey - don't insult applied physicists! I first heard about Bohmian Mechanics from one :)
 
  • #18
vanhees71
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Just because something is unobservable does not mean it is not intuitive. For example, I am sure you will agree that Feynman diagrams are intuitive but not observable. Perhaps you will say that Feynman diagrams are a tool which can be used to calculate something observable, but Bohmian trajectories can also be used as a tool to calculate something observable.

Finally, you can say that Bohmian trajectories are not intuitive to you, while Feynman diagrams are intuitive to you. That's fine, different people find different things intuitive. I do not recommend Bohmian mechanics to everybody. But I think I have a lot of experience on different views of QM that different people may have, and I think I can recognize who might like which interpretation. (Test me: Have I been right that you find Feynman diagrams intuitive, even though they are not observable?) From the words of Yasmin I've got a strong impression that Bohmian mechanics would satisfy him.
Feynman diagrams are very clever notations for formulas, but Bohmian trajectories are simply superfluous additions complicating the anyway complicated interpretation of quantum theory even further. Also, to apply (theoretical) physics to technology (engineering) philosophy doesn't help either :-).
 
  • #19
kith
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And my general advise would be to read old original literature from the people who came up with the stuff. It's always much more down to earth and not compress to minimum notation and at the same time generalized to the most general case which obscures anything.
On the other hand, you may have to do a lot of "translation" work when you get to more recent stuff. Also, some of the old papers are really obscure. I think you can easily spend as much time trying to understand Heisenberg's groundbreaking 1925 paper as on a well-written introductory textbook on QM.
 
  • #20
vanhees71
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Well, the drawback of reading old stuff is that you'll get a lot of the confusion of the early development of the theory. That's very interesting from a historical perspective and can help to understand the theory better. For that, however, it's good to be on firm ground concerning the physical content of the theory, and this is best achieved by reading good modern textbooks. My favorites are

J.J. Sakurai, Modern Quantum Mechanics
L. Ballentine, Quantum Mechanics, A modern development
S. Weinberg, Lectures on Quantum Mechanics

Particularly, for interpretational issues:

A. Peres, Quantum Theory: Concepts and Methods

Exceptions to the general rule are all papers by Dirac, Born, and Pauli, which are masterpieces in clarity. For maximal confusion, I recommend Bohr and Heisenberg :-).
 
  • #21
atyy
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L. Ballentine, Quantum Mechanics, A modern development
As vanhees71 and I have discussed many times, we disagree about Ballentine. My view is that Ballentine is between misleading to wrong on fundamental issues of quantum mechanics. Ballentine is an opponent of textbook quantum mechanics, and I say that the textbooks like Landau and Lifshitz and Weinberg are fine and correct.
 
  • #22
vanhees71
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Landau and Lifshitz are also great, but too much wave-mechanics oriented for my taste. The traditional way of teaching quantum mechanics in terms of wave mechanics seems to leave the impression in students that quantum mechanics is mostly about energy-eigenvalue problems (time-independent Schrödinger equations), and the dynamical aspects are not fully understood.

I like Ballentine for exactly the reason, for which atyy dislikes it. This only shows once more that the question of interpretation is not an objective part of the theory but very much due to the taste of each individual physicist, and you even can't decide, who's "right" or "wrong" on it, because everybody agrees on the predictions about observable phenomena, which is the only thing that really counts in physics, but I prefer the most simple interpretation (ensemble/minimal statistical) compared to interpretations that have additional elements, which are not really necessary but lead to large intrinsic (consistency) problems (like most flavors of Copenhagen with a collapse, with the exception of Bohr and his followers, who have an epistemic view on the quantum state) or add unobservable esoterics like Bohmian trajectories or Everet's parallel universes.

This shows that there are many philosophical problems, which I personally find very interesting, and I like to discuss them (not the leas in this forum :-)), but which on the other hand are (fortunately) not of much relevance for physics (let alone applied physics). E.g., it didn't matter much, which personal interpretation Shockley, Bardeen, and Brattain used when inventing the transistor ;-)).
 
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  • #23
atyy
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Landau and Lifshitz are also great, but too much wave-mechanics oriented for my taste. The traditional way of teaching quantum mechanics in terms of wave mechanics seems to leave the impression in students that quantum mechanics is mostly about energy-eigenvalue problems (time-independent Schrödinger equations), and the dynamical aspects are not fully understood.

I like Ballentine for exactly the reason, for which atyy dislikes it. This only shows once more that the question of interpretation is not an objective part of the theory but very much due to the taste of each individual physicist, and you even can't decide, who's "right" or "wrong" on it, because everybody agrees on the predictions about observable phenomena, which is the only thing that really counts in physics, but I prefer the most simple interpretation (ensemble/minimal statistical) compared to interpretations that have additional elements, which are not really necessary but lead to large intrinsic (consistency) problems (like most flavors of Copenhagen with a collapse, with the exception of Bohr and his followers, who have an epistemic view on the quantum state) or add unobservable esoterics like Bohmian trajectories or Everet's parallel universes.

This shows that there are many philosophical problems, which I personally find very interesting, and I like to discuss them (not the leas in this forum :-)), but which on the other hand are (fortunately) not of much relevance for physics (let alone applied physics). E.g., it didn't matter much, which personal interpretation Shockley, Bardeen, and Brattain used when inventing the transistor ;-)).
My objections to Ballentine are objective, not matters of interpretation.

Ballentine claims that textbook quantum mechanics is wrong, as he writes (p238) "In all cases in which the initial state is not an eigenstate of the dynamical variable being measured, the final state must involve coherent superpositions of macroscopically distinct indicator eigenvectors. If this situation is unacceptable according to any interpretation, such as A, then that interpretation is untenable." He suggests in one place (section 9.5) and claims in another (section 12.3) that there is experimental evidence against textbook quantum mechanics.
 
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  • #24
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Feynman diagrams are very clever notations for formulas,
They are more than that. How many times have you (or some of your colleagues) imagined that electrons "exchange virtual photons"? Even if you know that this is not what really happens, imagining that it does may help to create some intuition about abstract fundamental processes.

but Bohmian trajectories are simply superfluous additions complicating the anyway complicated interpretation of quantum theory even further.
There is no objective measure of "complication". Quantum mechanics with trajectories looks more complicated to you, but less complicated to someone else (otherwise nobody would like these trajectories in the first place). Don't represent your subjective feelings as if they were objective facts.

Also, to apply (theoretical) physics to technology (engineering) philosophy doesn't help either :-).
Not directly. But philosophy of physics helps in theoretical physics (example: Einstein), theoretical physics helps in experimental physics, experimental physics helps in applied physics, applied physics helps in industry, industry helps in making money, and making money helps in ... supporting those damn useless philosophers. :biggrin:

So you, as a theoretical physicist, can directly help only experimental physics, not applied physics (not to mention industry or making money). Does it make you feel worthless? I hope not. But then the philosophers of physics have the same right not to feel worthless themselves.

More generally, whatever ones place in the chain
philosophy-theory-experiment-application-industry-money
is, one has a tendency to think that his own place is the most distinguished one, because all to the left are less useful, and all to the right are less clever. I hope I don't need to explain what's wrong with such general tendency.
 
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  • #25
Another good method is the following: Type the name of the concept you don't understand (math or physics) into Google like this "appropriate name of math concept or words that make sense in that context pdf". Then open up every pdf you find as tab (if you know two or more languages you can do that in them too, I'm fluent in three languages therefore I can find a lot of stuff) then -> skim through every pdf until you understand it. This makes you familiar with the different approaches/notations and differences between math and physics and you will find an explanation that you can understand. It works 90% of the time. Of course you can do that with picture search too, but you will not have many results other like a few blogposts or something. For example I found a good introduction to homology on a computerscience blog, that's cool.
 
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