I personally believe in determinism and understand the basics of quantum mechanics, but don't see how any of it disproves that the universe is deterministic. Electrons cannot move change momentum or direction of momentum without an outside force, so its position cannot be changed without an outside force either. And if it does change, this should be predictable by the amount of energy and by the angle of the outside force. I don't think that a probability wave function shows randomness either. There should be reasons that electrons are more likely to exist at certain positions on a wave regardless of randomness.

  • here's a similar question. i hope you find the answers helpful. do you? all i know about QM is that (something called) hilbert space takes ages to work out!
    – user38026
    Apr 15, 2019 at 5:54
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    Your description is based on classical ideas that do not apply in QM. Electrons do not have positions or momenta, they only have a wave function, and its relation to measured outcomes is probabilistic, not deterministic. "Should be predictable", but are not, "should be reasons", but none that we know of, for example, for the electron to go through one slit rather than another in the double slit experiment. To save determinism you need to assume classical "hidden variables", which is an option, but the problem is that no one managed to detect them so far.
    – Conifold
    Apr 15, 2019 at 6:01
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    I would like to add to Conifold's comment, for the sake of notational clarity, that quantum mechanics doesn't disprove determinism, a specific interpretation of quantum mechanics calculus does. Apr 15, 2019 at 6:27

1 Answer 1


Certainly if some sort of new determinism exists in the quantum mechanical world, then it is different from the classical determinism. Before QM, you have positions and velocities and knowing these at one time would determine all subsequent positions and velocities. In QM, we think that there is a unitary evolution, so if we knew the wavefunction at one time, we could calculate the wavefunction for all subsequent times. But, the problem is, we dont know for sure if this is true. In the standard Copenhagen interpretation you have wavefunction collapse during measurement which if true would destroy even this version of determinism. Most sane people accept Copenhagen as operational way to derive experimental consequences from quantum laws, but equally sane people think that ultimately the evolution is deterministic in the quantum mechanical sense.

Then there is the classical dynamical chaos theory which were developed in the 1950-1970 time frame by Anosov, Kolmogorov, Sinai, and Arnold and others, this is the butterflies-wings idea which you may have heard of. It removes the possibility of even classical determinism as a useful idea.

So determinism is dead, but will not die completely.

  • > "chaos theory...removes the possibility of even classical determinism as a useful idea." It does not remove the status of determinism as a useful idea within philosophy. Chaotic systems are still classically deterministic, they're just too complex for us to (realistically) make predictions about outcomes. But we knew that already within philosophy (Laplace's demon) and still determinism had had a central place in the discussion about free will.
    – Chelonian
    Apr 15, 2019 at 13:47
  • In Laplace's time, it was thought that to predict 100 seconds into the future you might need 1cm accuracy in the positions now (assuming speeds of say 1m/s), with our present knowledge about the ubiquity of chaotic systems, we say to predict 100 seconds ahead we need 10^(-100) m accuracy. If you think this does not make any difference philosophically, that's fine with me, but then nothing ever discovered in science would or should necessarily compel the philosophers to change their views.
    – Kphysics
    Apr 15, 2019 at 19:12
  • Where are you getting those numbers? I'm curious about the sourcing. Also, I disagree with your last sentence: Why should one example of a scientific discovery not affecting philosophy mean that no such examples could affect philosophy?
    – Chelonian
    Apr 15, 2019 at 20:21
  • It is always possible, when faced with solid scientific evidence contrary to some abstract idea X, to say that no, it does not invalidate X absolutely. As indeed you seem to be doing.First there is Laplace's demon which people realized would have to be omnipresent and omnipowerful to be able to make predictions, then you are willing to ignore modern evidence that this demon would have to be also exponentially accurate in his measurements just to predict a short time ahead.And finally there is quantum mechanics which says you cannot measure position and velocity simultaneously anyway.Nt enough?
    – Kphysics
    Apr 15, 2019 at 20:34
  • Clearly it will not be enough for some people. Thats why I said poetically, "Determinism will not die completely."
    – Kphysics
    Apr 15, 2019 at 20:38

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