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> Show me the computations Just because computations exist that model a physical process to an arbitrary degree of accuracy doesn't mean we know what those com

• tsimionescu 1y ago
  But the reality is that we don't know if many of those things are computable. We just think it's likely they are, since the models we have of very simplified versions of them, or of very approximate versions, are computable. But no one can use a physical model or computer to precisely compute, say, the fall of sand (where the exact position and momentum of every grain of sand is precisely known) - so we have no actual proof that the actual physical process is computable. And, in fact, our best fundamental physical theory is not fully computable, at least in some sense - quantum measurement is not a deterministic process, so it's not exactly computable.
  • stevenhuang 1y ago
    QM is computable on classical turing machines, it is just not efficient.
    • tsimionescu 1y ago
      You can't compute the exact result of a quantum measurement. Now, randomness is a somewhat separate concept from computation. But still, a Turing Machine can't predict how a quantum system will behave after a measurement, so in some sense it's not computable. The best you can do is to compute the wavefunction and the resulting probabilities of the various possibilities.