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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: 3, Insightful) by aristarchus on Wednesday May 03 2017, @10:40AM (9 children)

    by aristarchus (2645) on Wednesday May 03 2017, @10:40AM (#503547) Journal

    Cuius erroris causa quod omnia quae quisque nouit ex ipsorum tantum ui atque natura cognosci aestimat quae sciuntur. 25 Quod totum contra est; omne enim quod cognoscitur non secundum sui uim sed secundum cognoscentium potius comprehenditur facultatem. 26 Nam ut hoc breui liqueat exemplo, eandem corporis rotunditatem aliter uisus aliter tactus agnoscit; ille eminus manens totum simul iactis radiis intuetur, hic uero cohaerens orbi atque coniunctus circa ipsum motus ambitum rotunditatem partibus comprehendit.

    Anicius Manlius Severinus Boëthius, Consolatio Philosophiae, Book 5 Prosa 4. Circa 524 AD.
    Boethius' use of this principle is quite contrary to the use that quantum physicists desire, however.

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  • (Score: 2) by AthanasiusKircher on Wednesday May 03 2017, @01:39PM (1 child)

    by AthanasiusKircher (5291) on Wednesday May 03 2017, @01:39PM (#503615) Journal

    At first I was confused by your quote, since Boethius is off on an argument about the knowledge of God and the possibility of predestination's compatibility with free will here, and the immediate context is a sort of Platonic form argument combined with different faculties of perception. Outside of that context, he certainly wasn't the first to note that apparent knowledge depends on the viewer (see Protagoras or Sextus Empiricus, for example) or that sight is a superior sense (e.g., Aristotle).

    But now I think I see your analogy here, and it's quite interesting. I still don't think Boethius had anything close to the physicists' epistemic relativism in mind here, but there's a connection between the temporal nature of perception and revelation in Boethius's example about a round body only "partibus comprehendit," compared to the atemporal "God's eye view." Given that this is all in the context of a free will discussion, the idea of possibility/probability is also implicitly involved in this act of gradual revelation.

    • (Score: 2) by Gaaark on Wednesday May 03 2017, @04:17PM

      by Gaaark (41) on Wednesday May 03 2017, @04:17PM (#503727) Journal

      Now, see this is why i like this site.

      Over on that other site, this conversation would probably go something like:

      "They don't know shite!"
      "You don't know shite!"

      Instead, we get intelligence and thoughtfulness and insight that makes me think.

      I'd eat you both up, but i don't like Soylent Red: i prefer the new Soylent Green.

      --
      --- Please remind me if I haven't been civil to you: I'm channeling MDC. ---Gaaark 2.0 ---
  • (Score: 0) by Anonymous Coward on Wednesday May 03 2017, @02:42PM (2 children)

    by Anonymous Coward on Wednesday May 03 2017, @02:42PM (#503649)

    I was actually going to point out that this kind of dilemma reminds me a lot of the clamor in medieval philosophy amongst people like Occam and Scotus, but I guess Boethius beat them by another 500ish years in some regards.
    I'm still impressed by the guy's intellect. Too bad he was executed before he could finish translating all of Plato and Aristotle.

    • (Score: 2) by aristarchus on Thursday May 04 2017, @03:10AM (1 child)

      by aristarchus (2645) on Thursday May 04 2017, @03:10AM (#504136) Journal

      Yes, but the Realist/Nominalist debate over the ontological status of general terms was very different than the "observational contamination of reality" debate of the modern realist/instrumentalist epistemological debates. The question is not whether the general conceptual structures determine or are determined by an independently existing reality, the question is whether there is any such reality. Both Duns Scotus and William of Ockham would be appalled!

      • (Score: 2) by Azuma Hazuki on Thursday May 04 2017, @03:53AM

        by Azuma Hazuki (5086) on Thursday May 04 2017, @03:53AM (#504160) Journal

        Personally I think this is one of those "has a dog the Buddha nature?" questions, which is to say, the answer is "this question is based on malformed assumptions." Reality may not be directly accessible to human consciousness, *and that's okay.*

        --
        I am "that girl" your mother warned you about...
  • (Score: 3, Insightful) by khallow on Wednesday May 03 2017, @06:04PM (3 children)

    by khallow (3766) Subscriber Badge on Wednesday May 03 2017, @06:04PM (#503805) Journal
    An English translation would be helpful here:

    The cause of this error is that every man believes that all the subjects, that he knows, are known by their own force or nature alone, which are known; but it is quite the opposite. For every subject, that is known, is comprehended not according to its own force, but rather according to the nature of those who know it.

    The problem with this assertion is that if it were merely a matter of the limitations of our perceptions, then why do we perceive things differently at all? For example, Boethius then speaks of perception of a sphere via sight and touch speaking of the sphere in terms of the senses in question while ignoring that both senses are more than sufficient to distinguish (at least at the implied scale) between a sphere and cube.

    Perception is not just a limitation. It is also a powerful delineation of reality. If we can't perceive a thing either directly or through its influence on things we can perceive, then in a very clear way, it doesn't exist to us.

    • (Score: 2) by HiThere on Wednesday May 03 2017, @11:32PM (1 child)

      by HiThere (866) Subscriber Badge on Wednesday May 03 2017, @11:32PM (#504048) Journal

      It's much worse than that. If all knowledge is only about what we know about things, then we can't say anything about things as such. Including that things as such exist.

      This is related to the interpretations of quantum theory, and why, e.g., it's impossible to rule out Solipsism.

      What we can say about a physical theory is that the evidence is consistent with certain interpretations. In quantum theory those interpretations include the (EWG) Multi-world hypothesis, Solipsism, a kind of pre-determinism, and several other interpretations that seem, on the surface, to be quite different. But even though they look quite different in English, they could all reasonably yield the same observed effects. My favorite interpretation is that the state vector never collapses, but that by observing we can determine certain features localizing our position in a branch of the state. But I can't rule out naive realism, or any of the other choices. The available evidence not only doesn't let you figure out which is correct, it doesn't even let you figure out the probability of one of the interpretations being correct.

      --
      Javascript is what you use to allow unknown third parties to run software you have no idea about on your computer.
      • (Score: 1) by khallow on Thursday May 04 2017, @02:52PM

        by khallow (3766) Subscriber Badge on Thursday May 04 2017, @02:52PM (#504337) Journal

        If all knowledge is only about what we know about things, then we can't say anything about things as such.

        It's not. Math is the huge exception to that. Nothing in math actually exists except as representations. But once you have a representation, no matter how convoluted or obscure - even if no one, universe-wide is ever aware of it, then the consequences follow.

        But even though they look quite different in English, they could all reasonably yield the same observed effects.

        Any theories with the same observed effects are the same. Then it just becomes a matter of what is more convenient to use to explain what we see.

    • (Score: 2) by AthanasiusKircher on Thursday May 04 2017, @09:01PM

      by AthanasiusKircher (5291) on Thursday May 04 2017, @09:01PM (#504530) Journal

      You're right about some of these issues, which is why I noted in my post that I was first confused by the citation of the passage. Boethius's argument makes a lot more sense when you read it in his broader context, but isn't really about the limitation of perception as it is about predestination and free will. I'm not going to bother getting into all of that here; you can read about it here [stanford.edu]. Basically, Boethius is just making a rough analogy to the differences between human and "God-like" perception here (which also, if you believe in predestination, includes knowledge of the future), not really a fleshed-out argument that's meant to say something deep about human perception.