Books about alternative interpretations of quantum mechanics Recently I've heard that there exist alternative interpretations of quantum mechanics which, while not as widespread as the Copenhagen intepretation (or so it would seem), are equally valid in the sense that they describe all the observable effects. Wikipedia mentions a few ones, the more popular of which seems to be the many worlds interpretation.
What are some books, suitable for someone with an undergraduate level knowledge of QM, that describe these alternatives? Something not too mathematical might be best for an introduction to the subject, but I'm not looking for a popular book either, of course.
 A: At first a big warning: Do not rely on stuff that you find on the Internet without further reference, there are many, many people, even recognized physics professors, who dont have a clue what they are talking about. Also, I would not recommend Deutsch's writings about MWI until you have a good understanding of the basics, until then, they are rather confusing.
For an elementary Introduction I would recommend the Stanford Encyclopedia of Philosophy (http://plato.stanford.edu/index.html), it contains good introductions to the various Interpretations such as MWI or CI.
Furthermore, a classic on this topic is "Jammer - The Philosophy of Quantum Mechanics", a very detailed description of the historical development and the different interpretations. If you want a detailed and precise overview over the relevant Interpretations, this book is for you, although its partially not too easy to read.
Apart from handpicked books, I would mainly recommend reading the original papers, especially the one by Everett, who is often cited very, very wrong. "The Theory of the Universal Wave Function" is even available online, i guess (must-read for everyone who is interested in Interpretation stuff). Apart from that, the most comprehensive collection of the original articles can be found in "Wheeler, Zureck(ed.) - Quantum theory and measurement". It contains most of the historically relevant articles. Surprisingly, they are mostly quite easy to read, the math does not exceed the level from elementary Quantum Mechanics.
Good luck, we need more people who know what they are talking about when it comes to interpretation!
A: Isham's book "Lectures on Quantum Theory" explains the formalism of quantum mechanics quite well.
David Deutsch has some lectures on quantum computation and quantum information that explains some issues in terms of the many worlds interpretation:
www.quiprocone.org/Protected/DD_lectures.htm.
Also see
http://xxx.lanl.gov/abs/quant-ph/9906007
http://xxx.lanl.gov/abs/quant-ph/0104033
http://arxiv.org/abs/1109.6223.
David Wallace has written many papers on the Everett theory:
http://users.ox.ac.uk/~mert0130/papers.shtml.
You might also find these books interesting after you have read the above:
http://www.amazon.co.uk/Many-Worlds-Everett-Quantum-Reality/dp/0199655502
http://www.amazon.co.uk/The-Emergent-Multiverse-according-Interpretation/dp/0199546967.
I should also say I think it is wrong to say the other interpretations are equally valid to the Copenhagen interpretation because they make the same predictions. The CI is a vague mess that imposes a distinction between stuff that has been measured and stuff that hasn't without specifying how the line is drawn. A prediction is not just a number: it involves an explanation of what happens in reality to bring that number about without which the prediction is not testable because you can always fudge about whether you did it properly or not. The CI does not provide any such explanation and so it makes no predictions.
A: The 2017 Springer book by Travis Norsen (Foundation of Quantum Mechanics) is an excellent and elementary introduction to the various interpretations of QM. Everything is presented following the historical development and there is also a careful selection from classical sources (articles, books, letters).
The author has in my opinion a (very slight) soft spot for pilot-wave and related ideas, but otherwise he's fairly unbiased in his account. I especially appreciated the clear headed analysis of relationships between non-locality and hidden variables.
Highly recommended.
A: Highly recommended:
Leslie E. Ballentine, Quantum Mechanics: A Modern Development, 2nd edition (World Scientific, 1998).
See https://en.wikipedia.org/wiki/Ensemble_interpretation
A: I enjoyed Tim Maudlin's Philosophy of Physics: Quantum Theory. It's very accessible to someone who is already familiar with quantum physics, and it gives a nice overview of the main "unorthodox" approaches: collapse theories, hidden variable theories, and many-worlds theories (though he is somewhat hostile to the many-worlds approach).
Sean Carroll's Something Deeply Hidden gives a nice defense of the many worlds approach aimed at a general audience (of fairly dedicated physics enthusiasts).
For physicists, both books are very accessible, yet stimulating and informative, especially if you're trying to learn the basics of interpretations of QM. They were very fun reads for me.
