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Physical laws: Descriptive or Prescriptive?

  1. Nov 3, 2005 #1
    Something that keeps cropping up in philosophical discussions is the nature of physical law. From time to time Mathematicians, physicists and philosophers give us reasons to believe that the world operates according to Platonic laws. Loop Quantum Gravity is just one recent example. For me though, this seems counter-intuitive. It seems more reasonable to expect laws to emerge from some underlying material framework -- after all, historically speaking, this is what we mostly observe of the world. Each time we successfully codify some emergent phenomena of nature we generally find ourselves describing some previously unrecognized material construct. Granted the classical materialistic view has been transformed almost beyond recognition by the 'new physics' of the 20th Century, but with no single conclusive Quantum interpretation at hand it seems prudent to reflect on past experience and assume that some as yet unrecognized material framework exists to explain all the Quantum phenomena as well.

    Thus to call on something totally untestable such as a Prescriptive laws from some inaccessible Platonic realm strikes me as unwarranted folly. What justification can there be for this approach?
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  3. Nov 3, 2005 #2
    Please convince me that Loop Quantum Gravity has anything to do with prescriptive, platonic laws. I'd love to discover that, but I think LQG says nothing on the subject.
  4. Nov 3, 2005 #3
    I think you might be right. It's something that has been atributed to Roger Penrose but having just looked into again it it seems that one of the most important principles in LQG is that there are no observers outside the universe. If all observers must be a part of the universe they are observing then their light cones will limit the information that is available, therefore the Platonic idea of absolute truths would not seem to be able to exist in a LQG universe.
  5. Nov 3, 2005 #4


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    Could you also please define "platonic law". I Googled it, checked the Stanford online dictionary, and unfortunatly came up empty.
  6. Nov 3, 2005 #5
    I love some of Plato's ideas, but I just figured that any physical theory that is so tied in with an unproven philosphy wouldn't get a lot of general respect. Look at QM for example, it can be interpreted in loads of ways.
  7. Nov 3, 2005 #6
    Excellent point. It's one of those terms that gets bandied about without too much care or thought. But there are some who believe that there are prescriptive laws governing the universe that somehow exist "out there" in a platonic realm. Generally this is the province of philosophers. So am I getting somewhere here -- have I simply been in the company of philosophers for too long and have started to swallow the BS?

    The problem is that ultimately everything seems to reduce to mysticism at some point whereby the philosophers say "told you so, everything your science is founded upon is nonsense".
  8. Nov 3, 2005 #7


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    Could you specify which philosophers believe or teach these prescriptive laws? Where in Plato is this taught? Certainly science has nothing to do with this idea.
  9. Nov 4, 2005 #8
    Philosophers David Armstrong, Fred Dretske, and Michael Tooley talk in terms of Universals:
    Paul Davies has this to say:
    Establishing the correct order of supervenience seems to be the main issue here. In our collective experience information or software is always seen to ride on the the material hardware of the cosmos. To argue for information to be prior to the material would seem to have an inbuilt disadvantage.
  10. Nov 6, 2005 #9
    The "way the world really is" is something that can never be known for certainty by an agent within such a world.

    Two reasons for this (which may be related at some deep level?) are Godel's incompleteness theorem and Heisenberg's uncertainty principle (HUP). Both place an in principle limit on our knowledge of the world we inhabit. Once we have distilled the "laws of physics" down to the quantum level then to go any further is pure speculation, metaphysics - we can never test any hypothesis that goes beyond the epistemic horizon created by the HUP.

    This is why there are (and always will be) so many opposing interpretations of QM. This is also why we will never be able to know whether the existing "laws of physics" are prescriptive, or simply descriptive and concealing some deeper material framework underlying QM.

  11. Nov 6, 2005 #10
    Thank you MF. This epistemic horizon that you speak of is clearly an impediment to anyone seeking to dispel dualism and other metaphysical concepts born out of philosophy. Do you have any words of comfort for the material realists out there?
  12. Nov 6, 2005 #11
    Tricky. I am one, you see.

    Unfortunately, from what I understand of QM, there is no way that we can ever "disprove" material realism. (I deliberately avoided saying "prove material realism", because, following Popper, no hypothesis is ever "proven" - the most we can ever say about any hypothesis is it either fits the facts or doesn't fit the facts).

    a la Bohm, there may be "non-local hidden variables" for example - this would be a materially realistic theory - but we could never carry out an experiment to test this hypothesis because the "hidden variables" are hidden by the HUP - and there ain't no way anyone is going to "see beyond" the HUP.

    So to your question - any words of comfort?

    Yes - don't give in to the indeterminists who insist on claiming that QM "proves" the world is fundamentally indeterministic - it does not!

    Time and time again I hear people who should know better claim things such as "the results of QM (complementarity, uncertainty, entanglement etc) have proven that there is no objective reality". This is absolute poppycock, born of poor education and bad interpretation. The results of QM prove no such thing!

    Keep the faith.

  13. Nov 6, 2005 #12
    There is a lively debate indeed, at least in the philosophy of science, regarding the nature of laws, whether there exist objective laws of nature, and how to make the difference between lawful statements and merely lawlike statements (though 'working' very well at a certain moment of time for all our practical purposes). Well so far no one could provide a satisfactory definition, without problems, though there have been enough many attermpts...The only gain was that we can at least provide some criterions which all candidates at the status of laws of nature should respect (logical and epistemological), without solving the problem once and forever however.

    One solution, a variant of necessitarianism proposed most prominently by Armstrong, is to use universals to make the difference between lawlike and and lawful statements. It has its merits but unfortunately has the important drawback of making unwanted ontological commitments, burdening the accepted ontology, besides in this view it appears that we should consider the universals more real than the objects they instantiate...My own, provisional, preference is a form of structuralism, without denying the possibility of strong emergence however, accepting also even the possibility that some non observables, even observables, and laws accepted by today's science might be simple tools 'working' well now for all our practical purposes. Indeed basically nothing should be hold as being 'set in stone' forever, nothing should be immune to being discarded, not even the basic assumptions of science.
    Last edited: Nov 6, 2005
  14. Nov 6, 2005 #13
    agreed - or the way I prefer to put it - The "way the world really is" is something that can never be known for certainty by an agent within such a world.

  15. Jan 14, 2006 #14
    I don't see why the HUP needs to limit our understanding of the way the world is. Afterall, the HUP *is* the way the world is.

    Placing a limit on our ability to observe doesn't limit our ability to fully understand and model the universe.

    You sound like someone who doesn't want to believe that nature may truly be probabilistic, or that the HUP is an innate part of nature, two things which MUST be taken at face value as being true. And once you take them as true, you neccesarily abandon any notion that you lack information on "how the world is".

    Are you claiming that the HUP neccesarily hides some underlying framework? How do you know that the HUP itself is not the framework? In our current reality it appears that the HUP is indeed the framework and is fundamental and essential and there is no evidence or reason beyond a determinist philosophy (or "religion" as some might call it since it would have to be based wholly on faith) to believe that.

    Your belief in the inability to fully understand the world seems no different than the belief in a supernatural power. You're making a hypothesis which is untestable by definition.
  16. Jan 24, 2006 #15
    At what point can we ever say we totally understand the world ? When would we ever be completely satisfied ? I suspect that complete total understanding of the world (universe ?, reality ? ) is not even conceivable since there is no way to even know when we have reached it. In the end it may simply be a subjective-emotional-aesthetical choice a scientist agrees upon. If you end up being able to completely manipulate reality to the point of being able to do anything you want, and this may be possible with simulated worlds inside computers or by directly modifying the neural circuits of human brains, then you have reached the end of science. Any model or imaginary metaphysics would do and be equivalent, it would no longer have any effect on the pratical usage of science.
  17. Jan 31, 2006 #16
    On Knowledge and Understanding!

    Yeah, that does seem to be their reaction doesn't it! :rolleyes:
    Yes, they seem to be! Now why do you think that might be so? :rofl: :rofl: :rofl:
    "Never be known? "Never" is a god awful long time! :biggrin:
    Why of course it doesn't; but does that prove the world is not indeterministic? At least I can prove there is no evidence of determinism; if you would consider reading my proof! :confused:
    Now here I can agree with you 100%. Suppose we start there with that as a fundamental hypothesis? :cool:
    Ah subodei, the great general of Genghis Khan; you're absolutely correct. And I can back it to the hilt. o:)
    Would you say one totally understood the world if I could give you an explanation which would exactly explain each and every phenomena which has ever or ever will be observed? :devil:
    Why should understanding the universe imply being able to completely manipulate reality? Can you give me a proof that anyone who understands something can completely manipulate it? I think you are dreaming! :tongue: :tongue: :tongue:
    I think you're sort of losing it in generalities. Prove one of them, if you would! :rofl: :rofl: :rofl: :rofl:

    Subodei, I have answered your note and, if you wish to have a discourse, post it here. :smile:

    Have fun -- Dick

    "The simplest and most necessary truths are the very last to be believed."
    by Anonymous
  18. May 16, 2006 #17
    Yes it is, isn’t it? But what is “time” anyway?

    The Heisenberg Uncertainty Principle already shows us that evidence for determinism (if it indeed exists in the world) is for the most part unreachable (beyond our epistemic horizon). This does not mean that determinism does not exist, it only means the evidence (for or against it) is (for the most part) unattainable.

    However – I can in fact demonstrate determinism does exist in some particular cases, even at the quantum level. Take a quantum object which has been “prepared” in a particular way (for example, let’s say a spin ½ electron, with it’s spin “up”). If I measure the spin of that electron in the vertical direction, I find it to be “up” (its been prepared that way). If I again measure the spin of the same electron in the vertical direction (without doing anything else to it), QM says there is a probability of unity (ie certainty) that I will find it to be spin “up”. If that is not quantum determinism, then what is it?

    OK, suppose we do?
    This would seem to lead to the conclusion that our fundamental beliefs about how the “world really is” are ultimately untestable, and must be taken on faith.

    How could one test your “explanation”? An exhaustive test (ie whether it does accurately explain each and every phenomenon which has ever or will ever be observed) is in practice impossible, therefore there is always room for doubt that one “totally understands”.
    In which case, we would have an “explanation” which appears to fit the facts (for the limited number of cases where it has been tested). This is exactly what any successful hypothesis does.

    Best Regards


    If one pays attention to the concepts being employed, rather than the words being used, the resolution of this problem is simple. (Stuart Burns)
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