Observers

Discussion in 'Physics & Math' started by arfa brane, Apr 18, 2017.

  1. iceaura Valued Senior Member

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  3. Confused2 Registered Senior Member

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    The cat business seems to be a failure.
    Could anyone suggest an actual example of the thing which the cat business is intended to model?
     
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  5. arfa brane call me arf Valued Senior Member

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    We're a two-cat family. One cat is black, the other grey and white. We call them Blackie and Graham for reasons known only to ourselves.
    Lately I've taken to calling the second cat Graham the Inseparable, in honour of Schrödinger.

    Sorry if that's no help at all.
     
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  7. arfa brane call me arf Valued Senior Member

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    Heads up folks, entanglement really is about complementary degrees of freedom, not particles.

    I think I can safely say that the entanglement resource in the qx chips is frequency--the qubits are frequency entangled.

    Anyhoo, if you can accept that Leonard Susskind knows what he's talking about, check out this online lecture in which he discusses entanglement between parts of the vacuum across an arbitrary boundary. You recall the vacuum, where there aren't any actual particles, but rather quantum fluctuations (for which a dual description exists).
    This duality is the important thing apparently, particularly if one dual description has at least one less degree of freedom than the other.
    Susskind also mentions that entanglement is important in quantum computing because it reduces the large Hilbert space to a smaller space, in other words it restricts the total degrees of freedom in a quantum system.

    So, is the vacuum a quantum system? Why, if it is, should that mean entanglement doesn't occur because there are no particles with charge or mass?
     
  8. The God Valued Senior Member

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    Degrees of freedom of/for what?
     
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  9. The God Valued Senior Member

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    Actually this is really weirdo.

    Why should the entanglement vanishes after observation?

    The wave function collapses on observation, fine; what happens to wave function after the observer is taken off, does it un-collapse itself?
     
  10. exchemist Valued Senior Member

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    Good question.
     
  11. The God Valued Senior Member

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    Rhetoric question! He will have no answer.

    Because his eureka moment is actually a confused entangled state due to tones of reading without proper sifting. Actually if you read too much on a subject like this, degree of freedom associated with rational thinking reduces drastically and you keep getting eureka moments.

    But nonetheless good thread by him.
     
  12. arfa brane call me arf Valued Senior Member

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    The ones Susskind talks about in that video, which I'm sure you haven't bothered to watch.

    But why should you? You already know everything, right?
     
  13. The God Valued Senior Member

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    Pl refer to first link, can you help in getting answers to below...


    1. What should be the correlation limit (Bell's view) between these (entangled) photons?

    2. What was the actual correlation leading to a conclusion that they are entangled?

    3. The detection of starlight color is a local process, in the context could that not have influenced the correlation?

    4. Is the claim of people involved in the project that since random generator based detector is just a few microseconds process while starlight was 500 light years earlier origin and hence we have pushed the matter by an order if 16, sensible? Is it not far fetched? How does it help?
     
  14. iceaura Valued Senior Member

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    It's oddly worded in the article - the limit is given by the inequality, above:

    Bell's Inequality: in classical world, given three properties A, B, and C of any collection of countable things,
    the number of them that possess A but not B, plus the number that possess B but not C, is equal to or greater than the number that possess A but not C.

    That is a fact of the normal world. : that {A but not C} cannot be larger than the sum of the other two. {A & -B} + {B & -C} is therefore an upper limit on {A & -C}. That is the limit referred to.

    As you can see, it holds in any collection of objects that either do or do not possess property B, communicate by cause and effect through space, and interact in ways that can be modeled in bi-valued logic (i.e. meaningful assertions of property possession are either true or false).

    That limit is violated, in these quantum world measurements of entangled systems. {A & -C} is larger than {A & -B} + {B & -C}.
    Dunno. Greater than the inequality allows, is the report.
    Partly dealt with in the last paragraph.
    Discussed in the article. It sharply constrains any hypothesis of communication between the entangled particle generator and the decision to measure a given property. It doesn't change anyone's mind, probably, but it does nail down one of the few remaining corners.

    The point was: the checks on this feature of quantum world - that it generates violations of Bell's Inequality - have been numerous, varied, and completely consistent. They have become routine - by now if an investigator failed to discover a violation their equipment or technique or experimental design would be doubted first, long before their results were accepted.
     
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  15. The God Valued Senior Member

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    Pl leave aside reference to hidden variable for a moment.

    1. Decision to measure a property was earlier based on on-board random generator.

    2. Decision to measure a property is now based on the color of incoming starlight photon (photon 500 ly old).

    Do you personally think that it is reasonable to conclude that they have pushed the hidden variable possibility by an order of 16 by using the starlight in place of random generator?

    Is it not correct to infer that electronics which was generating random number has become far more complex as the very detector now not only will interact with incoming photon but will analyse the wavelength too? You see earlier the number was generated based on some chips and a program....in latest experiment it is a different set of chips with a different and probably complex program. The decision is still based on certain criterion.
     
    Last edited: Jul 2, 2017
  16. arfa brane call me arf Valued Senior Member

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    That is largely why understanding entanglement is hard--the logic isn't Boolean. (In my opinion, but I estimate I'm not the only one with that opinion)

    You can't make any set of logically consistent statements about the state of particles (or their degrees of freedom), in some ensemble, which corresponds to a distributive Boolean lattice or a part of one. Quantum logic in fact forms a lattice which isn't distributive, or in which deMorgan's Law doesn't apply.

    But we know that superposition applies, and interference is easy to understand in that context. What about superposition and entanglement? Why is the relation, if there is one, different?
     
  17. Confused2 Registered Senior Member

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    After watching the Leonard Susskind lecture suggested by Arfa Brane

    I am left knowing less than I thought I knew before.
    Is it possible Susskind (clearly a Vulcan) et al are making assumptions about fields and particles that some of us aren't making?

    After drawing a bubble in space the field is continuous inside/outside your arbitrary bubble.
    IF 'the vacuum' is restricted to virtual PAIR production (possibly even if not) then the virtual particle and its mate can be both inside, both outside or one inside and one outside. Going with inside+outside we have entanglement between inside and outside which is still based on the production of individual entangled pairs - which is what the simple cat people seem to know about. Going back to the field which is continuous across the barrier even the inside virtual particles may not be exactly localised to the inside ... I think I've already gone far enough for someone to point out that I have entirely missed the point of the lecture.
     
  18. Confused2 Registered Senior Member

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    Possible recap .. again.
    To be entangled you need two (or possibly more) cats (with entangled states).
    Superposition is one cat with more than one possible state.
    Since cats are just a set of states that hang together and look like a cat it seems possible you might get entangled states without any cats but I don't know anything about that.
     
  19. iceaura Valued Senior Member

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    The whole cat thing was a guy - Schrodinger - setting up an in-your-face illustration of just how bizarre this newly postulated quantum world was, and asking "really?" In 1935.

    Basically, he's asking the quantum theorists, the new kids on the block: You guys really going to go to the mat with this?

    He imagined a cat in box, with absolutely no contact of any kind with anything outside the box - perfect seal. Not an arrangement anyone can make - a thought experiment. In the box, with the cat and likewise sealed off, is a poison gas emitter that, if triggered, kills the cat. (And fills the box with poison gas, and makes other changes to the inside arrangement, but these are ignored). Here's the catch: gas emission is triggered by the radioactive decay of a single atom of a radioactive element inside the box. That is a quantum event, whose equation establishes a superposed state: until observed, until interacted with "the environment", it both (or neither) has and has not happened.

    If it decays, dead cat. If it does not, live cat. Perfect seal - nothing out, nothing in, the entire system entangled. So the cat is entangled (Schrodinger apparently invented this use of "entangled", and we've been using it ever since).

    So the cat is and is not dead, is and is not alive, inside that hypothetical box - according to the new theory Schrodinger was challenging. Really?

    And the philosophical argument came into focus.

    Note: the year was 1935 - twenty years after Einstein suggested the absurdity of quantum theory to Schrodinger, thirty years before John Stewart Bell published his paper - which laid out a distinctly non-hypothetical kind of box one could set up for a particle one might as well obtain from a cat somehow, if poetry is the goal https://en.wikipedia.org/wiki/Bell's_theorem
     
  20. Confused2 Registered Senior Member

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    Please say if you think I'm just being too picky. If I knew more maybe I wouldn't be so picky.
    By a sort of majority count ( https://en.wikipedia.org/wiki/Schrödinger's_cat ) the cat (one cat) in the box is in a state of superposition. Only when the box is opened does the observer become entangled with the state the cat emerges in. Two alternative states after opening the box. Person + dead cat (person+cat=2 things) buries it. Person + live cat (person+cat=2 things) feeds it. Two things entangled. One thing (the cat) in a state of live/dead superposition.
     
  21. iceaura Valued Senior Member

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    The observer never becomes entangled, by definition.
    Observation destroys entanglement. Only one state is observed.
     
  22. Confused2 Registered Senior Member

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    Wiki can be wrong - I'm not setting up Wiki as an expert - just trying to read Susskind in a consistent way.
    https://en.wikipedia.org/wiki/Schrödinger's_cat
    I'm happy with local or global definitions - for the purpose of meaningful local communication it helps to have a consistent agreed definition.
     
  23. iceaura Valued Senior Member

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    That's a really unfortunate wording - what they are describing is not "the observer" becoming entangled with the cat, but the creation of a superposition of many observers - which inhabits a larger universe no one observer inhabits.

    I don't think that becoming many observers all observing different states of cat viability counts as making an observation. And that is not what Schrodinger meant by "entanglement", which as he pointed out is proposed to exist in this one, singular, uniquely observed universe.
     

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