Wigners Theorem And Linerarity

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With reference to the following lecture by Leonard Susskind :
http://www.newpackettech.com/Resources/Susskind/PHY30/LectureRv9_Video_Lec7.htm

Someone asked why evolution is linear - I was waiting for him to say - Wigner's Theorem implied it. But no - he said there is no deeper explanation - its simply an axiom of QM.

Anyone got any idea what he was getting at? Or am I mistaken and it really is a separate axiom?

BTW - superb lecture.

I believe he is releasing the lectures as a series of books. Already ordered the classical physics one and can hardly wait for the others.

Thanks
Bill
 
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The evolution is a consequence of Wigner's theorem + Stone's theorem, which do indeed depend on some hypotheses (axioms as you may call them): preservation of probability distributions under time evolution and the state space being a linear topological space.
 
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If we release an electron around a positively charged sphere, the initial state of electron is a linear combination of Hydrogen-like states. According to quantum mechanics, evolution of time would not change this initial state because the potential is time independent. However, classically we expect the electron to collide with the sphere. So, it seems that the quantum and classics predict different behaviours!
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