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

How strong are fluid experiments in restoring determinism?

  1. Nov 23, 2014 #1
    I am referring to this article:http://www.quantamagazine.org/20140624-fluid-tests-hint-at-concrete-quantum-reality/

    Only a handful of phycisists (John Bell being one of them) took the Bohm-interpretation of QM seriously, given it had no scientific falsification, Are those views likely to change now, given these recent findings, and unify QM with a fully deterministic model, at all times?

    Your views?
     
  2. jcsd
  3. Nov 23, 2014 #2

    Nugatory

    User Avatar

    Staff: Mentor

    Those water drops are an analogy for Bohmian mechanics, and they're a really neat visual aid. But an analogy will only go so far; they don't support the Bohmian model any more than observations of the planets orbiting the sun support the Rutherford model of the atom.

    (There are several threads on these experiments already - search this section of the forum using keywords like "droplet" and you'll find them).
     
  4. Nov 23, 2014 #3

    bhobba

    User Avatar
    Science Advisor
    Gold Member

    Precisely why do you want determinism? Whats so great about it? Those that practice and/or learnt about QM got used to it ages ago. I cant grasp exactly why anyone would think intuition develped in the common sense macro world applies outside it.

    QM is a very beautiful mathematical theory once you understand it. To me that more than enough - but that's just me.

    And therein lies the whole naked truth of this interpretation stuff. What interpretation you choose reveals more about your psychological motivation than nature. I guess it's no secret mathematical beauty and elegance, especially symmetry, counts a lot for me, but in reality its nothing but hubris on my part - experiment is, as always, the final arbiter.

    Thanks
    Bill
     
  5. Nov 23, 2014 #4

    atyy

    User Avatar
    Science Advisor

    The article http://www.quantamagazine.org/20140624-fluid-tests-hint-at-concrete-quantum-reality/ is very misleading.

    The achievement of Bohmian Mechanics is not to restore determinism. Bohmian Mechanics is one possible solution of what is known as the "measurement problem", which is how one might describe a reality that exists independently of observers, or equivalently why definite experimental outcomes are observed. Before Bohm, some people thought that such a solution might not exist. After Bohm, that view was proven wrong. That is the major achievement of Bohmian Mechanics.

    Since Bohmian Mechanics was discovered, many other solutions to the measurement problem have been found. To know which, if any, of the different solutions thus far discovered describes our reality will require experiments that falsify quantum mechanics.

    A major problem that has not been solved is an observer-independent formulation of physics which includes the relativistic standard model of particle physics. Even if such a solution is found, experiments will still be needed to decide if it is correct.

    The fluid experiments are fascinating, but irrelevant to Bohmian Mechanics, or any other alternative solution to the "measurement problem". One should also note that the fluid experiments are thus far only a weak analogy to quantum mechanics, not having reproduced quantum phenomena like entanglement.

    If you read in the comments section of the article in the OP, you will find similar comments by Tim Maudlin, who is an expert on Bohmian Mechanics.

    A good introduction to the measurement problem is John Bell's "Against 'measurement" http://www.tau.ac.il/~quantum/Vaidman/IQM/BellAM.pdf. An alternative class of proposals to Bohmian Mechanics for solving the measurement problem are those that propose spontaneous state reduction. A discussion of how those might be tested is found in Arndt and Hornberger's "Testing the limit of quantum mechanical superpositions" http://arxiv.org/abs/1410.0270. A proposal to test a particular version of a Bohmian-like theory is Colin and Valentini's http://arxiv.org/abs/1306.1579.
     
    Last edited: Nov 23, 2014
  6. Nov 24, 2014 #5
    We do have deterministic probabilities, going by the Schrodinger equation. I find it unsatisfying, however, why the universe would phenomenologically hid information from the "observer", if it's already determined. The microscopic/macroscopic world is intertwined. You cannot logically separate the two (the small and large) at any point in spacetime events.
     
  7. Nov 24, 2014 #6
    Then why is the entire paper devoted to it and headlined "supporting concrete quantum reality".

    [Moderator's note: Removed unnecessary argumentation]
     
    Last edited by a moderator: Nov 24, 2014
  8. Nov 24, 2014 #7

    Nugatory

    User Avatar

    Staff: Mentor

    Perhaps whoever chose the headline didn't read the article completely, so missed such important bits as
     
  9. Nov 24, 2014 #8

    DrChinese

    User Avatar
    Science Advisor
    Gold Member

    As Nugatory points out, this analogy only goes so far. There are lots of papers that "tend" to support a non-local deterministic view and a lot that support the exact opposite view. None of those are compelling in the end, despite the title and and despite the interpretations of others.
     
  10. Nov 24, 2014 #9
    Direct evidence and evidence is a capable distinction.
     
  11. Nov 24, 2014 #10

    atyy

    User Avatar
    Science Advisor

    The fluid experiments are no evidence at all for the Bohmian hypothesis. Samuel Johnson did much more for the Bohmian viewpoint, which is why this article is so misleading.

    http://www.samueljohnson.com/refutati.html
     
  12. Nov 24, 2014 #11

    bhobba

    User Avatar
    Science Advisor
    Gold Member

    The state, like probabilities, only allows us to determine the probabilities of the outcomes of observations. That the state is governed by a deterministic equation in no way changes the outcomes of observations are not deterministic - or to be more careful about it no mechanism is hypothesised on how an observational outcome is determined - we have interpretations that are deterministic eg BM. Its like if you had a dice with a weight inside that was shifted around by a motor. When you throw the dice the probability of a side comming up continously changes in a deterministic way depending on where the weight is. But the outcome is probabilitic, not deterministc.
    I wrote:
    Get it?
    That's one reason a lot of work has been done on decoherence because it allows the definition of an observation without dividing the world into macro/micro. That is now resolved - but others remain - although of course research is ongoing.

    Thanks
    Bill
     
    Last edited: Nov 25, 2014
  13. Nov 27, 2014 #12
    That's still determinism. In the words of particle physicist Lawrence Krauss: "All theories (interpretations) of quantum mechanics are deterministic, the measurments are indeterministic". "Once you start with the data set... (it) predicts unambigiously how the world will evolve in the future".
     
  14. Nov 27, 2014 #13

    bhobba

    User Avatar
    Science Advisor
    Gold Member

    Semantics on what's deterministic, not deterministic etc have been thrashed out of this forum over and over - they lead no-where.

    Nor does quoting physicists - on the issue of interpretations they vary wildly. Its an area you need to explain your views in your own words.

    Here are the facts. The system state evolves deterministically. But the system state is simply the codification of the probabilistic outcomes of observations - exactly analogous to probabilities from probability theory - in fact QM is the most reasonable generalisation of probability theory that allows the outcomes (called pure states) to vary continuously. Its exactly the same as the dice analogy. Depending on where the weight in the dice is, it changes the probabilities, but not the fact its probabilistic. The same with QM - the probabilities are replaced by the state. Indeed just like probabilities you cant even measure a state - all you can do is by measuring a large number of similarly prepared systems determine it to a very high degree of confidence - but strictly speaking you can never know it.

    Would you describe a world (like the dice analogy) where the probabilities of outcomes are deterministic as deterministic? I wouldn't - but hey - if you want to - go ahead - just make sure people understand what you mean by deterministic.

    Note - the above analysis is from the formalism of QM - interpretations have their own take - in some interpretations like BM the state is very real and everything is deterministic. That's the reason quoting physicists on issues like this doesn't help much - it purely depends on their interpretive context - I have zero idea what Krauss's is.

    Thanks
    Bill
     
    Last edited: Nov 27, 2014
  15. Nov 27, 2014 #14
    Of course I would. Determinism is well defined in physics and philosophy - unambigious path.
     
  16. Nov 27, 2014 #15

    bhobba

    User Avatar
    Science Advisor
    Gold Member

    Fine - we know what you mean by determinism, and what I mean.

    Thanks
    Bill

    [Moderator's note: Removed some rhetorical questions, as the thread is closed so there's no opportunity to respond to them]
     
    Last edited by a moderator: Nov 27, 2014
  17. Nov 27, 2014 #16

    Nugatory

    User Avatar

    Staff: Mentor

    We have drifted far from the original topic of this thread.
    It's time to cut it off.
     
    Last edited: Nov 27, 2014
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: How strong are fluid experiments in restoring determinism?
  1. Symmetry restoration (Replies: 0)

Loading...