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

The jewel found in Quantum mechanics?

  1. Dec 19, 2013 #1
    Could someone explain what this crazy new discovery means? Is it the rosetta stone of QM?
     
  2. jcsd
  3. Dec 19, 2013 #2

    bhobba

    User Avatar
    Science Advisor
    Gold Member

    I assume you mean this:
    https://www.simonsfoundation.org/quanta/20130917-a-jewel-at-the-heart-of-quantum-physics/ [Broken]

    Mate, right now, exactly what it means is uncertain. Its without doubt important - but how important remains to be seen. It may be paradigm changing or simply just a better way to calculate.

    Thanks
    Bill
     
    Last edited by a moderator: May 6, 2017
  4. Dec 19, 2013 #3
    Right, but I'm trying to grasp what they found, is it just a new equation or is it really some type of jewel. When will we realize that QM is alien intelligence looking at us right in the face.
     
  5. Dec 19, 2013 #4

    f95toli

    User Avatar
    Science Advisor
    Gold Member

    What they found is a set of equations, that when plotted in a graph LOOKS like a jewel.

    It is akin to saying that the equation y=x^2 is shaped like a bowl.
     
  6. Dec 19, 2013 #5
    It says what they found right on the first caption of that link from bhobba. The geometrical properties give rise to probability distributions of the outcomes of particle interactions.
     
  7. Dec 19, 2013 #6
    Ah , thank you for that explanation.
     
  8. Dec 19, 2013 #7

    bhobba

    User Avatar
    Science Advisor
    Gold Member

    Like I said what it's saying (in the sense of its meaning and significance) at the moment is uncertain.

    But as to what QM is that's not quite that mysterious these days:
    http://arxiv.org/pdf/quant-ph/0101012.pdf
    http://arxiv.org/abs/0911.0695

    Basically it would seem that ordinary probability theory and QM are the most reasonable ways to model physical systems as generalized probability models. What singles QM out is it allows entanglement - which ordinary probability theory doesn't.

    Thanks
    Bill
     
    Last edited: Dec 19, 2013
  9. Dec 19, 2013 #8
    There's one thing I don't really get from that article. They keep stating that "locality is a central pillar" in quantum field theory. But what could they possibly mean by that, considering the fact that quantum entanglement (which QFT should be consistent with) is well described by the opposite: non-locality.
     
  10. Dec 19, 2013 #9

    bhobba

    User Avatar
    Science Advisor
    Gold Member

    FT

    QFT has a different foundation than non relativistic QM that respects relativity so must be local. What Bell showed is QM objects cant have well defined properties independent of measurement context and be local. The answer is simple - simply assume QFT doesn't allow well defined properties independent of measurement context.

    Also note that non locality of the Bell type cant be used to send information FTL - which is the sense locality is meant - so its probably possible to accommodate non locality in QFT - but the simplest way to handle it is simply say it doesn't have properties independent of context.

    Thanks
    Bill
     
    Last edited: Dec 19, 2013
  11. Dec 19, 2013 #10
    Ahh ok, so there's basically two similar but still different definitions of locality. I'm from the quantum information side, and there locality almost always just mean that an object is local or nonlocal (like in Bell-type experiments).

    So just to get what you said, you mean that in QFT locality instead means: An event somewhere in space cannot be caused by something outside the light cone?
     
  12. Dec 19, 2013 #11
    It's local in the sense, I guess, that some properties (but not all of those that are required to send/construct information) could be "connected/joined" via another dimension....as if they were un-affected by space-time.
     
    Last edited: Dec 19, 2013
  13. Dec 19, 2013 #12

    bhobba

    User Avatar
    Science Advisor
    Gold Member

    In relativity it means information cant be sent FTL. Relativity doesn't strictly rule out non-locality - only the ability to send info FTL to sync clocks.

    Non local effects like Bell are allowed if they cant be used to send information. The easiest way to view QFT is it doesn't allow any type of locality violation - but if you want to make life harder, for whatever reason, it's still allowed if it cant be used to sent info FTL.

    Thanks
    Bill
     
    Last edited: Dec 19, 2013
  14. Dec 21, 2013 #13
    Please take the quoted material & commentary below as both/either general information for the OP, and/or responses to questions raised farther down the thread. I didn't want to break up the article quotations more than necessary!

    All from Natalie Wolchover, for Quanta (same as referenced by bhobba): A Jewel at the Heart of Quantum Physics

    Obviously the informal definitions highlighted above may be of use to Zarqon, others here:


    So for some questions of my own: Am I right to think that the disposal of 'locality' proffered in the article is closely related to the Holographic Principles/proposals associated with quantum gravity? I gathered that from language like in the quotations provided--especially the parts about black holes & horizons, and Planck scales. Is this new treatment of 'locality' invoked to avoid the problems (that I've often heard reference to) associated with continuous spacetime and those 'notorious' quantum infinites?? (Hope I'm on the right path here, at least! :smile:)

    Secondly, I have to admit, I was really surprised to see 'unitarity' (or rather the dispensation, thereof) held up beside 'locality' as a 'problem concept' to be eliminated(!). I would have expected exactly the opposite--I've always considered it (unitarity, that is) to be a pilar of physics beyond the standard model, and one of the key insights of recent times! Am I missing something with this? I'd guess that the reason behind it lies in the 'amplituhedron's' function as a practical tool for real-world calculations (like the rendering of predictions for particle scatterings, and measurements), rather than (e.g.) representing some idealized theoretical formalism.

    However, doesn't string theory have a similar picture (of interaction amplitudes), which is infamous for its deafening silence on what's happening 'on the inside' of such a universe (i.e. in time/away from unitarity, etc.)? Is there some key departure on the part of the 'amplituhedron' at this point? Or just, "Why is so much emphasis being put on the implications for our understanding of 'unitarity' exactly?:confused:"
     
    Last edited: Dec 21, 2013
  15. Dec 21, 2013 #14

    stevendaryl

    User Avatar
    Staff Emeritus
    Science Advisor

    Well, there are two aspects of quantum mechanics (or quantum field theory): (1) The evolution equations governing the fields, and (2) the interpretation of those fields as representing probability amplitudes for the results of measurements.

    Quantum field theory is perfectly local in aspect number 1: The evolution of the quantum fields in one region of spacetime depends only on the values of fields in the backward lightcone.
     
  16. Dec 21, 2013 #15
    I'd like to know more about this as well. How can we interpret systems in which the total probability isn't one?

    Also wasn't there a recent new method, called "the unitarity method" for calculating amplitudes really fast, bypassing the feynman diagram calculations?
     
  17. Dec 21, 2013 #16
    Good catch. That part interested me very much as well, but somehow it got lost on the way to market when I put together my post. :uhh:
     
  18. Dec 21, 2013 #17

    bhobba

    User Avatar
    Science Advisor
    Gold Member

    It cant be interpreted as probability - obviously - because one of the axioms of probability is the probability of all possible events must add up to one - see Kolmogorovs axioms.

    They will have to find some other way around it like the negative probabilities that plagued relativistic QM in the early days.

    Two issues here. First its a populist account bereft of the technical detail - not that I think even if that detail was published more than a few specialists in the area would understand it anyway. And secondly the article is basically saying it needs further investigation.

    Thanks
    Bill
     
  19. Dec 21, 2013 #18

    bhobba

    User Avatar
    Science Advisor
    Gold Member

    I think any reading into it beyond its something interesting that needs investigation by specialists in the area is not at this stage warranted.

    I think any attacks on unitarity will have a hard time contending with Wigners theorem:
    http://en.wikipedia.org/wiki/Wigner's_theorem

    We need to see exactly what develops.

    Thanks
    Bill
     
  20. Dec 21, 2013 #19
    The real paper is finally out, btw. I didn't realize the following was from a different thread: Finally... The Amplituhedron Paper!

    Also, thanks for the tip on Wigner's theorem. I'll have a look.
     
  21. Dec 21, 2013 #20

    bhobba

    User Avatar
    Science Advisor
    Gold Member

    At the math level this is at Wigners theorem would be ho-hum. They would know it backwards up down and sideways. I am pretty sure they have something a bit more subtle in mind.

    And no - I have zero idea what it is.

    But unless you are into it at that level its pointless really conjecturing - time will tell.

    Thanks
    Bill
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: The jewel found in Quantum mechanics?
  1. Quantum mechanics (Replies: 12)

  2. Quantum mechanics (Replies: 9)

Loading...