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

B Interpretation of entanglement

  1. Jun 12, 2016 #1
    Once I heard a fellow-layman on QM say that he imagined two entangled particles never been separated in the conceptual sense, that is: the two particles are conceptually 'one', only they connect two parts of spacetime, and are so able to exhibit correlations over spacetime with respect to the entangled property. So I think you could say then that entanglement is a kind of spacetime bending.

    Is such a view part of any existing interpretation, and if yes, which one?

    Thanks.
     
  2. jcsd
  3. Jun 12, 2016 #2
    I would think what you're referring to is the ER = EPR conjecture proposed by Maldacena and Susskind. Briefly the idea is that a duality exists between entanglement and Einstein-Rosen bridges (wormholes).
     
  4. Jun 12, 2016 #3
    Perhaps the Hidden Measurements Interpretation says something of that sort?

    ...we are forced to accept that microscopic quantum entities, like electrons, protons, etc., are not permanently present in space, and that only at the moment they are detected by a measuring apparatus, would a position for them be created. In other terms, the HMI indicates that when a quantum entity, like an electron, in a non-spatial (superposition) state is detected, it is literally “dragged” or “sucked up” into space by the detection system. And this means that our physical reality would not be contained in space, but the other way around[17]. To quote Aerts [21] :

    Reality is not contained within space. Space is a momentaneous crystallization of a theatre for reality where the motions and interactions of the macroscopic material and energetic entities take place. But other entities – like quantum entities for example – “take place” outside space...

    https://en.wikipedia.org/wiki/Hidden-measurements_interpretation
     
    Last edited: Jun 12, 2016
  5. Jun 12, 2016 #4
    It is true that two particles that are entangled are viewed as in one state rather that two things in separate states. Is that what you mean?
     
  6. Jun 12, 2016 #5

    Nugatory

    User Avatar

    Staff: Mentor

    That's unlikely to be a good starting point... Not impossible, but unlikely.
    That might be an attempt to wrap some words around the way that a quantum system, even a multi-particle one, is mathematically a single system described by a single quantum state. Statements like "I measured the spin of an electron at detector A and got spin-up" and "I measured the spin of an electron at detector B and got spin-down" are not statements about properties of electron A and electron B; they are descriptions of measurement results on a single multi-electron quantum system. That's just how the mathematical formalism works - it's part of the recipe for calculating the probability of getting various results from various measurements.
    There's no support whatsoever for that idea in the math, so...
    no.
     
  7. Jun 13, 2016 #6

    JK423

    User Avatar
    Gold Member

    I think a rigorous way to define, and consequently interpret, entanglement is the following:

    Given two separated and non-interacting quantum systems A and B, they are said to be entangled if and only if
    we cannot assign a definite quantum state to each system ( ##\sigma^k_A## and ##w^k_B##, respectively) independently of the state of the other system:
    ##\rho_{AB} \neq \sum_k p_k \sigma^k_A \otimes w^k_B.##
    In other words, the statistics that you get out of measuring entangled systems A and B do not correspond to statistics that "independent systems" produce, since the probability distributions do not factorize. Therefore, an entangled state describes "separated" and "non-interacting" quantum systems that are nonetheless "not independent" from each other.
    And this is the spooky/paradoxical/non-intuitive characteristic of entanglement!
     
  8. Jun 14, 2016 #7
    But, in the discussed experiments, those "separated systems" have nothing actually separating them, except their observers trying to impose their own separatedness on what they observe...
     
    Last edited: Jun 14, 2016
  9. Jun 14, 2016 #8

    JK423

    User Avatar
    Gold Member

    Indeed, sepatedness is not fundamental to entanglement per se. However we do use it in the argument in order to demonstrate clearly and beyond doubt how "paradoxical" entanglement is. If the systems are not separated, and therefore not independent from each other, it's not clear what's so special about entanglement. But, in any case, you are right and in the definition of entanglement that i gave above the word "separated" is not required.
     
  10. Jun 14, 2016 #9

    vanhees71

    User Avatar
    Science Advisor
    2016 Award

    If you have entanglement you have correlations between far-distantly measured observables. E.g., in the usual Aspect experiment setup you have polarization entangled biphotons whose polarization part is
    $$|\Psi \rangle=\frac{\sqrt{2}}{2} (|HV \rangle-|VH \rangle).$$
     
    Last edited: Jun 15, 2016
  11. Jun 14, 2016 #10

    JK423

    User Avatar
    Gold Member

    But as AlexCaledin pointed out, the particles don't have to be separated to be described by an entangled quantum state.
     
  12. Jun 14, 2016 #11

    DrChinese

    User Avatar
    Science Advisor
    Gold Member

    And entangled photons can be "separated" in time as well. Photons that have never co-existed can be entangled.
     
  13. Jun 15, 2016 #12

    bhobba

    User Avatar
    Science Advisor
    Gold Member

    Separated is not a property of entangled systems until observed to have it. You cant say nothing separates them any more than you can say the opposite. QM is silent on whats going on when not observed. That is one of the key things about QM that separates it from classical systems. Classical systems have properties independent of observation.

    Thanks
    Bill
     
  14. Jun 15, 2016 #13
    :smile: So, the Unitary Evolution is not going on?
     
  15. Jun 15, 2016 #14

    bhobba

    User Avatar
    Science Advisor
    Gold Member

    Yes. But like most things statements gain their meaning from context - here the context is observable properties.

    Thanks
    Bill
     
  16. Jun 15, 2016 #15
    But we know Bohr's words,
    “There is no quantum world. There is only an abstract quantum description.”

    - perhaps separateness and entanglement may belong to that abstract description rather than observed reality? For example, if the measured particles can be described by something like Feynman diagram connecting them with coherent lines, then they are entangled.
     
  17. Jun 15, 2016 #16

    bhobba

    User Avatar
    Science Advisor
    Gold Member

    As I have mentioned many times be very careful of what the early pioneers said.

    In fact, without going into it, Bohr's view was deeply flawed:
    http://scitation.aip.org/content/aip/magazine/physicstoday/article/58/11/10.1063/1.2155755 [Broken]

    To be specific QM is silent on if there is a quantum world or not - we have interpretations with all sorts of takes on that.

    Thanks
    Bill
     
    Last edited by a moderator: May 8, 2017
  18. Jun 15, 2016 #17

    "Physicists and their apparatus must be governed by the same quantum mechanical rules that govern everything else in the universe. But these rules are expressed in terms of a wavefunction (or, more precisely, a state vector) that evolves in a perfectly deterministic way."

    Well, if I got it right reading H. Stapp and others, such deterministic worldview must be wrong because it leaves no place for consciousness.
     
    Last edited by a moderator: May 8, 2017
  19. Jun 15, 2016 #18

    bhobba

    User Avatar
    Science Advisor
    Gold Member

    You got it wrong.

    Again QM is silent on if consciousness is involved or not - we have interpretations that use it - most don't.

    Stapp holds views quite a bit outside the mainstream.

    Thanks
    Bill
     
  20. Jun 15, 2016 #19
    Well, what Stapp actually holds, it's Heisenberg's onthology. He is showing that it's strongly supported by the new brain research.
     
  21. Jun 15, 2016 #20

    Nugatory

    User Avatar

    Staff: Mentor

    That phrase "going on" suggests some sort of ongoing process, that there's some physical thing that is evolving with time. That might be, but there's nothing in the math of unitary evolution that says that it has to be. We have an abstract mathematical object that we can subject to certain mathematical manipulations to find the probabilities of getting various measurement results at some place and time. We also have another mathematical manipulation, called "unitary evolution", which when applied to our original abstract mathematical object, will produce another abstract mathematical object that can be manipulated to find the probabilities of getting various measurement results at a given place at some later time. If you find it helpful to think of this unitary evolution as "something is going on" between the two times, you are free to do so - it's a very natural intuition. But there's nothing in the math to either confirm or deny that intuition.

    "Separateness" has a clear meaning - it's a property of points in spacetime. Quantum mechanics tells us the probabilities of getting various measurements results at these points. "Entanglement" is a mathematical property of the abstract mathematical objects that I described above, one that leads to sometimes surprising predictions for the probabilities of some measurements made at different points in spacetime. (@JK423 provided a good definition of this mathematical property above).
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Interpretation of entanglement
  1. On entanglement (Replies: 169)

  2. Entangled states (Replies: 7)

  3. Entangled particles (Replies: 8)

Loading...