Having been looking at lecture notes, online sources and books, the list of postulates of quantum mechanics seems to vary. For instance, some sources (my lecture notes, for instance) refer to $|\langle \psi _i | \Psi \rangle |^2$ as the probability of finding the system in a state $|\psi _i \rangle $on taking a measurement of observable whose eigenkets are the $\{|\psi _i \rangle \}$. While in an online source this is not given as a postulate, but the expectation value of an observable as $\int \psi * \hat A \psi $ or $\langle \psi | \hat A |\psi \rangle $ is. Clearly the former implies the latter, however.

I realise the development of quantum mechanics wasn't straihtforward, but I was wondering if there is a more authoratative source, perhaps by one of the founding fathers of quantum mechanics, which provides a widely accepted list for the postulates of Qm?

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    $\begingroup$ There is no such list. Different authors generally pick and choose on which of a number of equivalent formulations (such as the ones you metion in your question), what they regard as the core principles of quantum mechanics as apposed to extra information to be added later (for example writing more or less general versions of the Schrodinger equation), and to what extent they want to engage with questions about measurement. $\endgroup$ – By Symmetry Oct 5 '18 at 16:40
  • $\begingroup$ Well, link-cascading off your WP link, you are led to von Neumann's historically influential book; much water has passed under that bridge, since, however. The HSMse might be a better venue for your question. $\endgroup$ – Cosmas Zachos Oct 5 '18 at 19:38
  • $\begingroup$ please note that the postulates for a physics theory are the axioms from which a subset of the mathematical solutions ( mathematics has its own axioms) are chosen that describe the observations and predict new ones successfully. Think of the axioms for mathematical theories. Axioms are interchangeable with rigorously proven theorems and what was a theorem becomes an axiom. In mathematics it is simple to choose the most economical in formulas format, but in physics nothing is economical :). look at parallel postulate here math.brown.edu/~banchoff/Beyond3d/chapter9/section01.html $\endgroup$ – anna v Oct 6 '18 at 6:16

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