Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

A Building on QP from 5 reasonable axioms

  1. Dec 13, 2017 #26

    bhobba

    Staff: Mentor

    Ok - lets try different approach then.

    Look up Euclid's axioms. Then look up Hilbert's axioms.

    Do you see a difference? If so describe it - if their is no difference then explain why - that would mean, for example, explaining how something with length but no width can exist.

    One is the kind of axioms physicists use - the other mathematicians. The difference lies at the foundation of the two disciplines.

    Thanks
    Bill
     
  2. Dec 14, 2017 #27

    Fra

    User Avatar

    I am not sure I understand your presumed argument from this comparasion and to the foundations of physics?

    The difference between Euklides and Hilbert is around 2000 years, so the late 19th century critique against Euklides non-stringent meothds, such that arguments proofs where based on drawing geometrical figures - while valid critque today - seems a bit unfair to be honest and Euklides isnt here to defend himself ;)

    Hilberts ideas holds a higher deductive level. But what can we expect even from a bright mind that lived over 2000 years ago? We might instead wonder what a person like Euklides might have done if he was born in the 20th century.

    Also the critique of Euklides was not based on physics, its was more on the logical system level. I also see neither of Euklides nor Hilbert as physicists (or natural philosphers). I am not critiquing the foundations of probability theory - as a mathematical theory.

    In physics OTOH, the probloem is different, so its hard to compare. The kind of postulates that are the assumed connection between model and experiment are fuzzy. We can never analyze that purely in terms of deductive logic. I think of physics as a tool to predict and control our environment in order to survive. Here development of matehmatics indeed goes hand in hand with physics. Ideally thinking as a physicists, it see the development mathematical theories here because they are of utility to us. This does not justify that we loose contact with nature, and mistake mathematical possibility for physical possibility.

    But i think you mean that there are different levels of stringency in the logical system used. Then I agree.
    And in physics there is a different level of "analysis" for how deep into the mud we need to attach our "postulates"?

    Maybe we just disagree on how deep into the "physical mud" we need to have our foundation?

    /Fredrik
     
  3. Dec 14, 2017 #28

    bhobba

    Staff: Mentor

    It's based on the level of abstraction used.

    Euclid's axioms speak of things that don't really exist as if they actually do. Yet nobody, even 12 year old's its taught to, has any problems drawing diagrams and making deductions from it. Hilbert is entirely abstract - no attempt at all in made to make it an actual model of something.

    That's the difference between axioms used in physics and those in math. Those in physics are written in a form that are directly applicable and assume a bit of 'common sense' on the part of the student, those in pure math are simply deductions from assumed axioms.

    Probability is different again - both pure and applied mathematicians have the same axiom's - the Kolmogorov axioms. Applied mathematicians have zero problems at all applying it because as part of a probability course they gradually build up the idea, via example, what an event etc is, just like in Euclidean geometry in the form presented by Euclid the teacher guides you to that understanding. Philosophers argue what it means, but in practice its of zero concern.

    Or maybe there is a lack of understanding of the difference between pure and applied math. In applied math you have a model that is mapped in some way to intuitive ideas we have of things like events, points, line, observations etc. It is part of applying it developing that intuition. Most of the time its so obvious nobody worries about it. When you studied Euclidean geometry did you say to your teacher - hey you said points have position and no size - these things you draw are not like that - how can that be? I think the piece of chalk that would be chucked your way would require considerable reflex to dodge, as the rest of the the class gave you a strange look. Of course actual points have size - but its obviously irrelevant to proving theorems etc. You are concerned about things that in practice are of no concern. Now in philosophy they likely worry about this sort of stuff - they worry about all sorts of strange things there - but in physics we use a bit of common-sense just like the teacher expected the class to use and without doubt you did without complaint when you were taught it.

    If such things interest you - that's fine - but its not science - its philosophy and not what we worry about here.

    I think most physicists are not concerned about such things, I certainly am not, and hold views similar to Weinberg:
    http://emilkirkegaard.dk/en/wp-content/uploads/Steven-Weinberg-“Against-Philosophy”.pdf

    You may say - that what's wrong with modern physics or similar things. I have been posting on science forums for years and have heard it all.

    I cant prove it of course - but history shows the kind of things that worry you basically lead nowhere.

    Thanks
    Bill


     
    Last edited: Dec 14, 2017
  4. Dec 14, 2017 #29

    Fra

    User Avatar

    As I see it, these things are of no major concern for just maintaining status quo ocurrent established scientific knowledge.

    But I think they are of deepest concernt for making progressions in the foundations of physics.
    Unfortunately I suspect a causal relation between these two statements of yours, which i also mentioned in the other thread ;-)

    Yes, I extracted this point of you of yours from the other thread, and i certainly respect your perspective. Indeed I do realise that my perspective is in minority.

    However, no researcher should be seriously discouraged by the failure of others. The optimistic attitude is obviously that all the other failed because they didnt do it the right way. Statistically most who think like that fail, but if none think like that progress will be stalled. What you label philosophy is IMO essential for progress of foundational physics.

    But I am as sure that i will not convince you to you change your understand no more that you will change mine :)

    /Fredrik
     
  5. Dec 14, 2017 #30

    bhobba

    Staff: Mentor

    Lets leave it at that then.

    If the words of Weinberg are not enough, and the utter failures he mentions of similar approaches to what you want to do, are not enough, then I think that's where we have to leave it.

    Thanks
    Bill
     
  6. Dec 14, 2017 #31
    This got me to thinking. There is some principal that a system should be able to evolve to maximum entropy. Perhaps, this can form the core of an argument that the transition probabilities are symmetric. This might also not pan out at all ...
     
  7. Dec 14, 2017 #32

    Fra

    User Avatar

    [bayes theorem] P(T|S) = P(S|T) * P(T)/P(S)
    and
    [ergodic hypothesis] P(S) = P(T)
    => P(T|S) = P(S|T)

    or were you seeking something more subtle?, this applies only to pure microstates though.

    /Fredrik
     
  8. Dec 14, 2017 #33
    Clever argument. The fly in the ointment is that since P(T|S)=P(S|T), then we always will have P(T)=P(S), even when not at equilibrium. The analysis needs to take place in a somewhat more complex context: P(T|S) manifests itself when a measurement is done for T, in initial state S, and vice versa for P(S|T).
    It is sufficient to work with microstates (pure states). Symmetry for mixed states would then follow from linearity of the transition probabilities.
     
  9. Dec 15, 2017 #34

    Fra

    User Avatar

    Yes if we are introducing another state (some macrostate) which "equiliirium" refers to, then one needs to make that explicit in the formulas, ie we are then not just talking about an uncertaint microstate, but also an uncertain macrostate. Its also along these paths, and when associating the macrostate to an observer as an inferential agent in its envirnoment, and ponder about its "expectations on evolution", then you can connect arrow of time to the observer depedent directions
    that you start to get into the objections i had before.But i will not ramble too much about that, becauase is am quote sure most arent going to see my point anyway and this is the wrong place to explain my whole idea anyway. But i think there is alot of interesting stuff in these inferential structures! So good luck with your paper, without know what stance you take!

    /Fredrik
     
  10. Jan 14, 2018 #35
    The paper was turned down by the journal, for reasons that I accept -- "this is an interesting mathematics article, but does not contain sufficient philosophical/conceptual insights to be publishable in ...". This is quite reasonable, given the nature of the journal. I raised two such insights in this thread
    1. Symmetry of probability of state transitions.
    2. The physical states (states that exist in reality) are topologically closed.
    However, I did not make a point of underlining these, and other issues in the paper, as I am not trained in physics, and feel it would be presumptive of me to espouse physics to physicists. So, I am in something of a quandary ...
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted