Speakable and unspeakable in quantum mechanics

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1. catpoliceSep 2015
   For various reasons, in quantum mechanics, one typically excludes the observer from the system being modeled. This is obviously problematic, especially if you're doing large scale cosmology. But that's the measurement problem for you.

   Regarding the context, the quote I'm thinking of comes from one of the essays in Speakable and Unspeakable in Quantum Mechanics, which is an enlightening read, both in terms of content and for its historical value. The issue, I think, is that the kind of 'conspiracy' implied by superdeterminist theories, wherein nature sort of guides our hand in picking certain experimental settings so as to hide information seems troubling to many scientists. See Zeilinger's quote at https://en.wikipedia.org/wiki/Superdeterminism

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2. selimthegrimSep 2014
   John Bell's book of lecture notes, "Speakable and Unspeakable in Quantum Mechanics"
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3. jostylrFeb 2014
   Tough question. The reason you probably did not understand them is that there are reasons are faulty.

   The textbook QM says that when experiments happen, the continuous wave function evolution stops and a new wave function is used in its place, chosen randomly based on a prescription using probabilities coming from the original wave function's decomposition in terms of an operator's (matrix) eigenvalues. This is a postulate in their view and that's that.

   It makes no sense since what is an observation? They don't explain. They just know it. They use it when doing their experiments and it works well enough. Attempting to formalize it leads to wrong conclusions.

   Bohmian mechanics/pilot wave theory is a deterministic, hidden variable theory that works. Within that context, you can understand the rise of operators as observables and the entire collapse rule which turns out to be a convenient approximation to reality in this theory; no actual collapse occurs. There is just one wave function on configuration space (3n dimensional space, n being the number of particles in the universe) evolving continuously via Schrodinger's equation and the particles themselves being guided by the wave function. It is the configuration space for the wave function where nonlocality arises from. Understanding its role in relation to relativity is the key question to understand.

   The wave function evolves with lots of its branches being irrelevant which is why we can effectively get rid of them, i.e., collapse the wave function.

   As for resources, I recommend the stanford page I linked to above. There is also http://www.bohmian-mechanics.net which has a great deal of material including an introduction: http://www.bohmian-mechanics.net/whatisbm_introduction.html and some faq videos http://www.bohmian-mechanics.net/videos_faq.html

   I like Bell's book of his articles, Speakable and Unspeakable in Quantum Mechanics. A wonderful read from a master.

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