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Question:
I understand that the positions and momentums of elementary particles is described in terms of probability theory in quantum mechanics. Is probability theory the "ultimate" explanation for the "states" of elementary particles, or will future scientists find descriptions or models in terms of something more fundamental than current models that does not use probability theory?



Replies:
Good question. Unfortuantely, we can't possibly answer it, because we don't know what will be discovered in the future. The probabilistic model of quantum mechanics has bothered physicists since it came out, but so far nobody has found a better model (or even another model that works as well). A lot of folks would LOVE to find a different model, though. So, we'll certainly TRY to find "descriptions or models in terms of something... that does not use probability theory," but I can't say what will actually be found. We just don't know!

Richard Barrans Jr., Ph.D.


You're not really asking a question about physics, are you? I mean, a physical theory can't possibly encompass a description of its own limitations, any more than you can see what you can't see because it's behind you. Follow? What you've got here is a question of metaphysics, the study of how we know what we know. I suppose it is conceivable that someone could, using pure logic and mathematics, come up with some kind of constraint on the nature of physical theory, and thereby show that certain kinds of theories -- for example those that involve only perfect certainties, like classical mechanics -- can't describe reality. That would be quite interesting. But I don't see how it could be done. Anyway, no one's ever done it.

Incidentally, you may read somewhere that Bell's Inequality and related experiments on photo polarization teleportation establish something along the lines you're thinking. This would be nonsense. The work in question, while quite interesting for a variety of other reasons, only shows on this score that the known forms of purely local mechanics (i.e. classical mechanics) are not consistent with experiment. Which we knew already, long ago.

Dr. C Grayce


You are asking a question not in physics but in metaphysics, or, if you prefer, a metaquestion about physics: a question about the nature of the questions that physics can (and cannot) answer.

Whether we will always find ourselves working with probability in our fundamental physics depends on whether the Universe is deterministic. If the Universe is deterministic, then everything that has happened or will ever happen is now and forever fixed, down to the last wiggle of the tiniest particle at the other end of the galaxy ninety billions years hence. Beginning from a complete description of the Universe at any single instant in its history, a mathematical computation can be made of the exact value of any measurable quantity at any other time.

If and only if the Universe is deterministic can there someday be a theory of mechanics that is not probabilistic.

We don't yet know if the Universe is deterministic. Quantum mechanics says it cannot be macroscopically observed to be so, but that is not the same thing.

Furthermore, assuming the assertions of quantum mechanics stand up for all future time unaltered would seem rash: Newtonian mechanics appeared to be the final theory of mechanics for almost 300 years. Quantum mechanics only 65 years old.

Let me also point out that even if human scientists never construct a more correct mechanics, that does not imply that such does not exist. It is not obvious that all knowledge is within the capability of our intelligence to deduce and comprehend. You would hardly doubt that a horse could never comprehend calculus -- the most correct theory of mechanics may analogously be beyond the grasp of homo sapiens.



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