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posted by Fnord666 on Wednesday May 03 2017, @07:39AM   Printer-friendly
from the so-it's-what-you-know,-not-who dept.

Arthur T Knackerbracket has found the following story:

One of the most striking features of quantum theory is that its predictions are, under virtually all circumstances, probabilistic. If you set up an experiment in a laboratory, and then you use quantum theory to predict the outcomes of various measurements you might perform, the best the theory can offer is probabilities—say, a 50 percent chance that you'll get one outcome, and a 50 percent chance that you'll get a different one. The role the quantum state plays in the theory is to determine, or at least encode, these probabilities. If you know the quantum state, then you can compute the probability of getting any possible outcome to any possible experiment.

But does the quantum state ultimately represent some objective aspect of reality, or is it a way of characterizing something about us, namely, something about what some person knows about reality? This question stretches back to the earliest history of quantum theory, but has recently become an active topic again, inspiring a slew of new theoretical results and even some experimental tests.

If it is just your knowledge that changes, things don't seem so strange.

To see why the quantum state might represent what someone knows, consider another case where we use probabilities. Before your friend rolls a die, you guess what side will face up. If your friend rolls a standard six-sided die, you'd usually say there is about a 17 percent (or one in six) chance that you'll be right, whatever you guess. Here the probability represents something about you: your state of knowledge about the die. Let's say your back is turned while she rolls it, so that she sees the result—a six, say—but not you. As far as you are concerned, the outcome remains uncertain, even though she knows it. Probabilities that represent a person's uncertainty, even though there is some fact of the matter, are called epistemic, from one of the Greek words for knowledge.

This means that you and your friend could assign very different probabilities, without either of you being wrong. You say the probability of the die showing a six is 17 percent, whereas your friend, who has seen the outcome already, says that it is 100 percent. That is because each of you knows different things, and the probabilities are representations of your respective states of knowledge. The only incorrect assignments, in fact, would be ones that said there was no chance at all that the die showed a six.

-- submitted from IRC


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  • (Score: 0) by Anonymous Coward on Wednesday May 03 2017, @05:45PM (2 children)

    by Anonymous Coward on Wednesday May 03 2017, @05:45PM (#503790)

    If it was just what we know, tunnel diodes wouldn't tunnel and die shrinks wouldn't be so challenging. On the experimental side, if it was just what we know, sodium atoms wouldn't tunnel through a diffraction grating too fine to pass a sodium atom.

    I'm no expert either way but I would be very surprised if no one could come up with a non-quantum explanation for the observations behind these claims if significant motivation was involved.

  • (Score: 2) by sjames on Wednesday May 03 2017, @06:44PM

    by sjames (2882) on Wednesday May 03 2017, @06:44PM (#503836) Journal

    There's been a long time to do so and plenty of motivation. But each and every experiment shows that Heisenberg's uncertainty isn't just a limitation of measurement, or measurability. In a sense, it's a limitation on the resolution of reality itself.

    If there's a deterministic layer below that, we haven't the slightest clue on how to probe it.

  • (Score: 1) by khallow on Wednesday May 03 2017, @07:54PM

    by khallow (3766) Subscriber Badge on Wednesday May 03 2017, @07:54PM (#503897) Journal

    but I would be very surprised if no one could come up with a non-quantum explanation for the observations behind these claims

    Sure, God willed it so, for example.

    But if you're looking for an explanation that will pass empirical muster, you will inherently have a non-classical explanation. Quantum is merely the label for that.