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 Jan 1 comment Reading Paul Dirac's “Principles of Quantum Mechanics” @OmnipresentAbsence I agree, original is best. I can say that Dirac's Principals of QM was the first book on QM I ever read that made any sense to me. Dec 29 comment Could fast vibrations cause us to travel forward in time @KyleKanos Well the point of the post was to show that it would involve temperatures at which a person would melt in a few seconds, whereas it seemed immediately obvious to me that the first would not work. Dec 29 revised Could fast vibrations cause us to travel forward in time edited body Dec 29 comment Could fast vibrations cause us to travel forward in time @lionelbrits Thanks for catching the J. As for the formula, I know there exists a hyper-relativistic expression for the thermal velocity but I couldn't find it after some searching so used this one to give an estimate. I should mention that though. Dec 29 revised Could fast vibrations cause us to travel forward in time edited body Dec 28 awarded Excavator Dec 28 answered Could fast vibrations cause us to travel forward in time Dec 28 awarded Editor Dec 28 revised Why does kinetic energy increase quadratically, not linearly, with speed? fixed typo Dec 28 suggested approved edit on Why does kinetic energy increase quadratically, not linearly, with speed? Dec 5 answered Is it possible to derive the formula of the gravitational potential energy without using the formula for the force Oct 31 comment Basic Interpretation of Compostion of Observables and their Measurement ... to the kind of idea I think you're trying to get it. It certainly feels like there should still be something going on... Oct 31 comment Basic Interpretation of Compostion of Observables and their Measurement Just to make sure we're on the same page, an observable is defined as a Hermitian linear operator whose eigenvectors suffice to form a basis. For such operators, or observables, $A,B$, it is not hard to show that they commute iff their product is an observable, which amounts to their product having a basis of eigenvectors. Thus in the formalism of q.mechanics at least, if they don't commute then their product ceases to be observable as its possible observations don't suffice to characterize the physical system at hand. I would agree, however, that this may not be a very satisfactory answer... Oct 31 awarded Supporter Mar 12 awarded Teacher Mar 12 answered How do we show that no hidden variable theories can replace QM?