Quantum mechanics

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Those who are not shocked when they first come across quantum theory cannot possibly have understood it. ~ Niels Bohr

Quantum mechanics is a first quantized quantum theory that supersedes classical mechanics at the atomic and subatomic levels. It is a fundamental branch of physics that provides the underlying mathematical framework for many fields of physics and chemistry.

Quantum mechanics is sometimes used in a more general sense, to mean quantum physics.

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I think I can safely say that nobody understands quantum mechanics. ~ Richard Feynman
  • For those who are not shocked when they first come across quantum theory cannot possibly have understood it.
    • Niels Bohr, quoted in Heisenberg, Werner (1971). Physics and Beyond, 206, New York: Harper and Row.
  • However unfamiliar this direct interparticle treatment compared to the electrodynamics of Maxwell and Lorentz, it deals with the same problems, talks about the same charges, considers the interactions of the same current elements, obtains the same capacitances, predicts the same inductances and yields the same physical conclusions. Consequently action-at-a-distance must have a close connection with field theory.
  • I think I can safely say that nobody understands quantum mechanics.
  • If the price of avoiding non-locality is to make an intuitive explanation impossible, one has to ask whether the cost is too great.

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It's always fun to learn something new about quantum mechanics. ~ Benjamin Schumacher
There is no quantum world. There is only an abstract physical description. It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about nature. ~ Niels Bohr
  • God does not play dice with the cosmos.
  • Do not presume to tell God what to do.
    • Niels Bohr, In response to Albert Einstein's quote.
  • If that turns out to be true, I'll quit physics.
    • Max von Laue, Nobel Laureate 1914
    • Talking about de Broglie's thesis on electrons having wave properties.
  • Anyone wanting to discuss a quantum mechanical problem had better understand and learn to apply quantum mechanics to that problem.
  • To the electron: may it never be of any use!
    • J. J. Thomson
  • Anyone who is not shocked by quantum theory has not understood a single word.
  • The very nature of the quantum theory ... forces us to regard the space-time coordination and the claim of causality, the union of which characterizes the classical theories, as complementary but exclusive features of the description, symbolizing the idealization of observation and description, respectively.
  • There is no quantum world. There is only an abstract physical description. It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about nature.
  • Very interesting theory - it makes no sense at all.
  • I myself only came to believe in the uncertainty relations after many pangs of conscience…
  • Had I known that we were not going to get rid of this damned quantum jumping, I never would have involved myself in this business!
  • One does not get an answer to the question, 'What is the state after collision?' but only to the question, 'How probable is a given effect of the collision?' From the standpoint of our quantum mechanics, there is no quantity which causally fixes the effect of a collision in an individual event. Should we hope to discover such properties later ... and determine [them] in individual events? ... I myself am inclined to renounce determinism in the atomic world, but that is a philosophical question for which physical arguments alone do not set standards.
  • A philosopher once said, 'It is necessary for the very existence of science that the same conditions always produce the same results.' Well, they don't!
  • The paradox is only a conflict between reality and your feeling what reality ought to be.
  • We have always had a great deal of difficulty understanding the world view that quantum mechanics represents. At least I do, because I'm an old enough man that I haven't got to the point that this stuff is obvious to me. Okay, I still get nervous with it.... You know how it always is, every new idea, it takes a generation or two until it becomes obvious that there's no real problem. I cannot define the real problem, therefore I suspect there's no real problem, but I'm not sure there's no real problem.
  • Marvelous, what ideas the young people have these days. But I don't believe a word of it.
  • Quantum mechanics is very impressive. But an inner voice tells me that it is not yet the real thing. The theory produces a good deal but hardly brings us closer to the secret of the Old One. I am at all events convinced that He does not play dice.
  • It seems hard to look in God's cards. But I cannot for a moment believe that He plays dice and makes use of 'telepathic' means (as the current quantum theory alleges He does).
  • What nature demands from us is not a quantum theory or a wave theory; rather, nature demands from us a synthesis of these two views which thus far has exceeded the mental powers of physicists.
  • However I cannot seriously believe in it because the theory is incompatible with the principle that physics is to represent reality in space and time, without spookish long-distance effects.

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