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I Is quantum weirdness really weird?

  1. Oct 26, 2016 #1
    The so called weirdness of quantum theory seems to be widely publicised particularly in the non specialist popular literature. However many of the experts in this forum seem to be of the opinion that there are rational explanations to much of the weirdness. What I would like to know is the following:

    Are there certain aspects of quantum theory that are considered to be weird, even by the experts? If so what are they?

    Thanks for reading this.
  2. jcsd
  3. Oct 26, 2016 #2

    A. Neumaier

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  4. Oct 26, 2016 #3
    Thanks for the reply. I scanned through the first pages of the thread you started but need to go through it more thoroughly later on when I get time. One thing that caught my attention was post 60 by Ohwilleke where he drew up a list of things that he stated were "totally weird". But only brief reference was made to the list and that was by yourself. Perhaps it's referred to later in the thread. I will take a look.
    Do you personally think there's nothing weird at all in all areas of QM. What about something I recently read about which, in a nutshell, claimed that a neutron and its spin can separate and move in different directions, However, the account I read was given in New Scientist, a popular layman type magazine.
    Thank you.
  5. Oct 26, 2016 #4


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    How do you define "weird"?
  6. Oct 26, 2016 #5


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    Well, the poster is asking for other people's opinions about whether it's weird, rather than giving his own opinion. So his definition of weird is not too relevant.
  7. Oct 26, 2016 #6

    A. Neumaier

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    I don't think this is possible; the mathematics does not allow this. Please give a precise reference to where you read it.

    I don't think anything is weird in quantum mechanics. It takes a while (and a lot of math) to understand how things make sense but then everything makes a lot of sense. The relative amount of weirdness perceived is (as a rule of thumb) roughly one minus the relative amount of understanding. (However as you can see from the discussion, not everyone here shares my view.)
  8. Oct 26, 2016 #7
    Thank you A.Neumaier . The article in question is entitled LOST AND FOUND and is published in VOL THREE/ISSUE THREE............ NEW SCIENTIST THE COLLECTION. The title on the front page of the magazine is THE QUANTUM WORLD. As I said New Scientist is a layman type magazine and they really do emphasise the weirdness. Despite that I can highly recommend this particular issue of the magazine. There's 127 pages and they refer to many different areas of QM including Duality, Zeno effect, Casimir effect,Entanglement, Aharanov Bohm etc.

    The article on the neutron refers to an effect known as the Cheshire cat phenomenom. In the article Aharanov states "I believe these are true physical properties of a quantum system". I'm assuming that a report on the experimental work has been published in a peer reviewed journal and I will search and try to find a reference.
  9. Oct 26, 2016 #8
    The article was published online in Nature Communications 29 July 2014. The title of the work is:
    "Observations of a Quantum Cheshire Cat in a Matter Wave Interferometer Experiment"
  10. Oct 26, 2016 #9

    A. Neumaier

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    If you want weirdness you can get it in many ways in the quantum world. That's why we have many worlds interpretations, virtual particle fantasies and Chesire cats. But if you want, you can also get it all in a much less spectacular and much more intelligible way. In the present case:

    The paper Quantum[/PLAIN] [Broken] Cheshire Cat’ as simple quantum interference." New Journal of Physics 17.5 (2015): 053042 by Correa et al. contains an explanation of Aharonov's Chesire cat phenomenon without any weirdness.
    Last edited by a moderator: May 8, 2017
  11. Oct 26, 2016 #10
    Interesting .Thank you.
  12. Nov 6, 2016 #11
    I'd say it's weird, and people claiming otherwise are just pretending to know more than they actually do.
    Let's face it, if someone told you that no matter which two of a set of three hidden coins you pick, they'll always show opposite sides, it would be pretty weird, right?
    Well, QM does almost that. It doesn't claim they'd always be opposite, but it can make it so they are opposite 75% of the time, more than the 66% limit a rational explanation can provide.
    And as if that weren't weird enough, it then goes on and says the coin you didn't pick can never be checked.
  13. Nov 7, 2016 #12


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    It depends on your definition of "weird"
    QM certainly "makes sense" if you go through the math and if you work with it for long enough you get used to most aspect of "quantum weirdness".
    That said, this does not change the fact that much of QM defies our "intuitive" understanding of the world; this is one reason for why "tools" such as the Bloch sphere are so helpful if you want to get some intuition for what is going on.

    Also, note that the there is a lot of "weird" things in classical physics and even math as well. I can fully understand the solution to "paradoxes" such as the Monty Hall problem, but this does not change the fact that it is counter-intuitive.
    My intuition for how things "should be" does not work here, nor does it always work in QM.
  14. Nov 7, 2016 #13


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    More likely, they're using a different definition of "weird".

    If one interprets "weird" as meaning "defies the common sense expectations we've acquired from a lifetime lived in a classical world", as is the rest of your post does, the quantum mechanics is indisputably weird.

    If one interprets "weird" as meaning "defies the rules of logic so that it is impossible to form an intuition about it no matter how much you work with it", which is roughly what @A. Neumaier is doing in #6, then it's not so weird, and becomes less weird the longer you work with it.
  15. Nov 7, 2016 #14


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    First you need to define weird and have everyone agree.

    What everyone agrees is its often counter intuitive - which is not quite the same thing.

  16. Nov 7, 2016 #15


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    Strong claims that - that you have divined the truth and others are just deluding themselves.

    Exactly what is 'weird' about the following:

    It brings the BIG issue with QM into focus (how a classical world emerges from a a theory that assumes it is observations in such a world from the start). But weird - that's another matter.

  17. Nov 7, 2016 #16
    I think this thread is weird because it asks what people think is weird.

    there is no objective definition of what is weird.

    I in no way can think that nature is weird because it implies nature has some sort of purpose / agenda or that nature has a set of moral standards which is just anthropomorphising imo.
  18. Nov 7, 2016 #17


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    So you're saying that it would be weird if nature cared about human sensibilities? :wink:
    That's the reason I say that QM is weird, because it seems to care about things such as measurements, which are only defined in terms of interactions that are useful for increasing knowledge about the state of the world.
  19. Nov 7, 2016 #18
    I could not disagree more with this;

    so you have just promoted QM to that of a sentient being that cares about stuff, specifically measurements.

    I find your statement weirder than weird - but I not sure what the word is for that.

    anyhoo as someone once said - every person is some other person's weirdo
  20. Nov 7, 2016 #19

    Simon Phoenix

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    To borrow a term from Heinlein, I tend to really want to 'grok' stuff, to feel it in my bones, so to speak. Some would seem to argue that this grokking is not the job of physics but that physics is just a means to predict observations and if it does that then who cares what's "really going on"? I find that epicyclic view a little bit too mechanistic for my tastes.

    QM is, for me, fascinating and beautiful and deeply mysterious. I want to really grok QM, but so far my conclusion is that it's un-grokkable except in a rather abstract way.

    Take Bell's most famous work, for example. It starts off by saying that there really are properties of things, independent of measurement. We can, in principle, attach numbers to these properties - we might not be able to measure them, and we might only be able to treat them statistically, but the starting assumption is that these properties exist. But if we do that then we run into trouble and our predictions fail at some point. To me this means that nature is not behaving in a way that is describable with the assumption of well-defined properties independent of measurement. I suppose there's a philosophical point here to do with the relationship between our models and 'reality', but it seems to me that if nature really were operating with objects that had properties independent of measurement then it is possible in principle to model that with non-contextual variables.

    To attempt to wax lyrical I would say that the upshot of this is that deep down there are no 'properties', just possibilities, and what we call 'reality' emerges (probably via decoherence) from this underlying ocean of potentialities.

    Does that qualify as 'weird' or 'strange'? I think at the very least it qualifies as being bloody odd given our everyday experience.
  21. Nov 8, 2016 #20


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    I was making a little joke, but I guess it missed its mark.
    Last edited: Nov 8, 2016
  22. Nov 8, 2016 #21
    I get things....eventually.
  23. Nov 8, 2016 #22
    cos2(pi/6) = 0.75 covering "rationally" 60/90 of the relevant angles.
  24. Nov 8, 2016 #23


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    Haven't you heard? Your'e not allowed to make jokes, about science.

    The funniest thing I've ever heard, from a scientist, regarding QM, was, that; "It's stupid". [see below]

    I've not a clue about how QM works, so I'll not comment further, regarding the OP.

    [below] Professor Roger Bowley [5:54]; "I think that quantum mechanics is so totally counter intuitive, that it seems stupid to everybody."

    I'm a tad daft, when it comes to words. so "weird" and "stupid", in the context of this question, are the same.

    ps. Do Maxwell's equations qualify as "QM"? I've always thought they were a bit weird.

    Maxwell; "Ok. You take an electron, and throw it over there. In the process, a type of screwy, ratchet wrench type thing happens. Now, I'm not saying it's weird, as it's quite obvious that this is what really happens, but......"
  25. Nov 8, 2016 #24
    Your reference says Axiom 5 rules out classical probability theory (PT). I don't know what this means in spite of being familiar with PT.
    Does QM in general rule out PT? Is it necessary to change some of the axioms or definitions of PT? Can you explain this in your own words without giving me a reading list?
  26. Nov 8, 2016 #25
    In order to prove the 66% value for the quantum coins it is necessary to assume all three coins have particular values (sides) in spite of the fact you only get to see two of them. This requires the assumption of realism = counterfactual definiteness. Perfectly reasonable for classical coins, but after thinking about it for a long time I no longer find it ironclad in general. And there goes the weirdness since you won't get the 66% for quantum coins.
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