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About self-measurement in entangled system

  1. May 2, 2014 #1
    I am trying to understand something about the problem of self-measurement in entangled system, I will try to do an example, please help me:

    If we have an isolated system with two entangled, conscious, microcomputers, one, δ with 1 hour cell, and the other β with a 10 hours cell.
    Here I am considering consciousness as subjective experience (Chalmers 1995), that could be present or not in the same individual.

    After 59 minutes the situation should be still:
    ψ=1/√2(lconscious δ>lconscious β>+l unconscious δ>l unconscious β>)

    But after one hour what happen? Could the death of the microcomputer δ be considered a self-measurement that has the ability to collapse the system in ψ= l unconscious δ>l unconscious β>
    leaving the other microcomputer β to work for other 9 hours without consciousness?
    Or, after the "death" of δ, the situation with only β alive will remain unchanged with
    ψ= 1/√2(lconscious δ>lconscious β>+l unconscious δ>l unconscious β >), because a system cannot measure completely itself?
     
  2. jcsd
  3. May 2, 2014 #2

    bhobba

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    Concious microcomputers - haven't heard of those :rofl::rofl::rofl::rofl:

    But I think I get your drift.

    You seem to be caught up in a very fringe interpretation, namely conciousness causes collapse. It had a bit of a following many years ago with guys like Wigner and Von Neumann being adherents for reasons there is no need to go into here - if you are interested in that you can start another thread.

    Bottom line is with our better knowledge of decoherence it has now become a very fringe interpretation - in fact Wigner when he heard of some early work on decoherence by Zurec abandoned it realising the original reason for introducing was no longer required. If collapse even occurs is very interpretation dependant.

    If you check out a modern development of QM such as Ballentine you will see collapse is not required, and isn't even part of the formalism (again without going into the details):
    https://www.amazon.com/Quantum-Mechanics-A-Modern-Development/dp/9810241054

    If the concious microcomputer 'died', it would be simply part of the quantum evolution of the system of no more import than any other change in the system - from the viewpoint of QM that is.

    One thing that needs to be mentioned is the reference you gave to Charmers is about philosophy which by forum rules is off topic here. Also if your exposure to QM is via philosophers I strongly suggest you check out a 'proper' text like Ballentine - unfortunately many philosophers (not all by a long shot, but many) leaves a lot to be desired.

    If you want to pursue this matter further on this forum you will need to stick to the physics.

    Thanks
    Bill
     
    Last edited by a moderator: May 6, 2017
  4. May 3, 2014 #3
    Dear Bill,

    Thank you for your answer.

    My example is not strictly related to the Von Neumann/Wigner interpretation, I have written consciousness, but it could be every other attribute of microcomputers.
    Thank you for your book suggestion. Personally I am more inclined to Collapse point of views as GRW or others.

    But, although you think that it is no more required, could you, please, tell me what would happen to the system under the collapse point of view?

    Thank you in advance for your help.
     
  5. May 3, 2014 #4

    bhobba

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    Which collapse version? There are a few.

    I will take Copenhagen. In that interpretation collapse is simply a change in the propensity of outcomes similar to when you throw a dice. Before it is thrown each face has an probability of one sixth, after being thrown one side has probability one, the rest zero.

    That said your thought experiment doesn't really involve QM at all because death is entirely determined by the voltage of a battery. Once it falls below some value one microcomputer is dead. That's entirely predictable classically, like flipping a coin is entirely predictable from the forces etc.

    Thanks
    Bill
     
  6. May 3, 2014 #5
    Dear Bill,

    Thank you for accepting to discuss my example with a Collapse interpretation.

    Yes, the death of the microcomputer δ is determined by the battery. This is the motive of the choice of the consciousness among the many attributes of the microcomputers.

    But the two microcomputers are entangled, so if before the death of δ the situation was

    |ψ>=1/√2(|conscious δ> |conscious β>+ | unconscious δ> | unconscious β>), after the death of δ , the situation, with only β alive, will remain unchanged with
    ψ>= 1/√2(|conscious δ> |conscious β>+ | unconscious δ> | unconscious β >), or reduced to

    | ψ>= | unconscious δ> | unconscious β> , with microcomputer β living for other 9 hours deprived of its own consciousness?
     
  7. May 3, 2014 #6

    Nugatory

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    How are they entangled? That is, what physical process was used to prepare that initial non-factorizable state?
     
    Last edited: May 3, 2014
  8. May 3, 2014 #7

    bhobba

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    Exactly.

    What you are considering is classical.

    Generally speaking macro objects (and microprocessors are macro objects) being decohered by the environment are not entangled which is a peculiar state of affairs where the state of one object depends on the other, and to remain that way in general either needs to interact weakly with the environment such as photons or are isolated from the environment which is very very difficult. But even if somehow done how are they entangled in the first place.

    Thanks
    Bill
     
    Last edited: May 3, 2014
  9. May 3, 2014 #8
    Obviously the system is isolated as I wrote in my first letter.

    The entanglements should be obtained aproximately in that way:

    1) source of entangled photons
    2) two polarizers
    3) two Schrodinger's hammers (one per microcomputer) carefully calibrated, that, if the photon pass through the polarizer, the hammer hit the microcomputer causing the lost of consciousness without causing the death of the same microcomputer
     
  10. May 3, 2014 #9

    bhobba

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    The mentioning of the isolation thing was just by the by - but its very important. Even in deep interstellar space stray photons from the CBMR is enough to decohere macro objects and destroy superposition. Its a technological tour de force demonstrating quantum behaviour for even microscopic objects - it has been done but it is really really hard. For microprocessors demonstrating conciousness, man that is way out there - we don't even have large computers demonstrating conciousness - leaving aside exactly what that is which is a massive can of worms.

    'Schrodinger's hammers' - sorry don't know what they are. Are you somehow linking this to Schroedinger's cat?

    If so be aware the so called Schroedinger's cat paradox is trivial. The observation happens at the particle detector - everything is purely classical from that point on. The cat is never in a superposition of alive and dead. The purpose of Schrodingers cat was to demonstrate a blemish in Copenhagen's partitioning of the world into classical and quantum. In Copenhagen QM is a theory about observations that appear in an assumed classical world. But that classical world in at rock-bottom quantum so how can such a theory explain itself? In modern times that blemish has been removed, to a large extent the result of a better understanding of decoherence, but some issues still remain.

    OK, now a question for you. Do you know the difference between a pure and a mixed state?

    In Schroedinger's cat the cat is not in a superposition, but in a mixed state because everything from the particle detector on is classical:

    1/2 |alive><alive| + 1/2 |dead><dead|

    See:
    http://www.ipod.org.uk/reality/reality_decoherence.asp [Broken]

    In your example its correct state is:
    1/2lconscious β>lconscious δ><conscious δ|<conscious β|
    + 1/2lunnconscious β>luconscious δ><unconscious δ|<unconscious β|

    The difference is CRUCIAL, but before going further I need to know what you know about mixed states.

    There is a genuine issue here that lies at the heart on modern interpretations of QM to do with proper and improper mixed states, but it is not what you may think. And how the system is prepared is crucial to it.

    But just to pre-empt it you may find the following of interest that explains this crucial difference:
    http://philsci-archive.pitt.edu/5439/1/Decoherence_Essay_arXiv_version.pdf

    Thanks
    Bill
     
    Last edited by a moderator: May 6, 2017
  11. May 3, 2014 #10
    Nothing is truely isolated from the environment - in fact what you consider is entangled with everything else in the world (Quantum Enigma by Bruce Rosenblum). But being entangled with the environment is not sufficient to destroy superposition - it is merely entanglement with the environment that takes place. Decoherence simply takes into account that we are ignorant of the full environmental state and thus end up with what looks like classical probabilities as to the final state of the system + environment.
     
  12. May 3, 2014 #11

    bhobba

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    That's where the crucial difference between proper and improper mixtures comes in, but I don't want to go into that until I know what the OP knows of pure and mixed states.

    But just to pre-empt it all I think the OP has, once the details are fleshed out, a variation on Schroedinger's cat.

    That is mostly, but not strictly, true. However it would take us too far afield to delve deeply into it. Suffice to say it has proven possible to decouple some very small objects (but macro compared to subatomic particles) from the environment well enough to show strange quantum properties:
    http://physicsworld.com/cws/article/news/2010/mar/18/quantum-effect-spotted-in-a-visible-object

    Thanks
    Bill
     
    Last edited: May 3, 2014
  13. May 4, 2014 #12
    For Schroedinger's hammer, I mean an extremely small device able to cause the lost of consciousness without kill the microcomputer.

    Regarding the consciousness, I am taking it in the simplest way, i.e. the subjective esperience, that you have when you are awake and you not have when you are sleeping without dreams.

    Regarding the quick decoherence, the present feasibility of the experiment is not the main point. Maybe it could be made in the future, with extremely small nanocomputers and extremely small nano-Schroedinger hammers, for msec time.

    Considered all the ideal situations, not now available, that are able to maintain the two microcomputers myraculosly quantum entangled, with their situation described by a typical entanglement equation |ψ> relative to the conscious - unconscious states of the two microcomputers.

    My question in my previous letters was only this one: being the death of the microcomputer δ caused by the end of battery after one hour, the same unchanged entanglement equation |ψ> will describe the situation with only β alive?
     
  14. May 4, 2014 #13

    bhobba

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    Ok.

    But I have zero idea how that will entangle the two microcomputers.

    Can you please elucidate.

    Thanks
    Bill
     
  15. May 4, 2014 #14
    As I wrote before, is not my main goal to realize, now, the entanglement experiment. All the thought experiment is only to illustrate my question, so, please, consider for a moment that the two microcomputers are really entangled, and described by the equation |ψ>. After the death of δ, for battery end, the equation |ψ> will remain completely unchanged describing the situation with only β alive?

    Thank you for your help.
     
  16. May 4, 2014 #15

    mfb

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    Entangled in which quantity in which way? This is not a question about practical details, but about the experiment you look at.
     
  17. May 4, 2014 #16

    bhobba

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    In thought experiments you must specify the details, not leave some things handwavey and up in the air.

    That creates a mixed state - not a superposition. I claim what you are talking about is a mixed state, not an entangled superposition, by the very physical basis of what you are doing. You can't handwavey say suppose it wasn't.

    If you cant detail how they are entangled then you have to consider what you are talking about is unrealisable so basically meaningless - which I think it is. Conciousness is a very abstract thing (and an emergent phenomena as well that depends on large collections of objects), not something that can be entangled - which is why me and others in this thread are insisting on details. You can entangle photons, electrons etc - but conciousness - that has me beat.

    Here is an amusing take on this sort of thing:


    This sort of thing crops up every now and then in physics. For example some bright spark figured out a way to instantaneously transmit information by (somehow) cloning a quantum system. Wow. The only trouble is that 'somehow' turned out to be not possible. And its easy to see as well - if you could do it then you would violate the uncertainty principle - clone a system - measure with arbitrary accuracy the position in one and momentum in the other. These are cautionary tales of why details are vitally important.

    Thanks
    Bill
     
    Last edited by a moderator: Sep 25, 2014
  18. May 4, 2014 #17
    I would say no. It would take a further measurement to determine the state. Even if we measure after an hour, we simply create the history of collapse that says the system supposedly collapsed after an hour.
     
  19. May 5, 2014 #18
    Dear Bill,

    You are right, I apologize, I will try to re-arrange the experiment trying to meet your requirements:

    We have two nanocomputers δ and β able to do, many operations, including calculations of problems stored in their memory. Everything at extremely low temperature in an isolated system. Nanocomputer δ has a 100 picoseconds battery, nanocomputer β has a 1000 picoseconds battery. Each nanocomputer has an extremely sensible surface that if hit by a photon causes the start of the calculations.
    The entanglement should be obtained perhaps in that way: a source emits single photon that passes through a beam splitter that directs it to one nanocomputer or the other. The path is not detected so the photon should be considered to go both ways at once. So the system should be described by |ψ> = |calculating δ>|calculating β> + |uncalculating δ>| uncalculating β>.
    After 10 picoseconds nanocomputer δ die for the battery end; in your opinion,after 100 picoseconds, the above equation will remain unchanged |ψ> = |calculating δ>|calculating β> + |uncalculating δ> |uncalculating β>, even if there is only β alive?

    Thank you
     
  20. May 5, 2014 #19

    mfb

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    How can both (or none) be calculating?
    I think it should be |ψ> = |calculating δ>|uncalculating β> + |uncalculating δ>| calculating β>.
    To avoid decoherence, you would probably need something like reversible computing, and even then it is a purely hypothetical situation - but that's fine, we can use that.

    A computer without battery cannot calculate, so your state goes to
    |ψ> = |calculated, now dead δ>|uncalculating β> + |uncalculating (still dead if battery was used) δ>| calculating β>
    So what?
     
  21. May 5, 2014 #20

    bhobba

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    OK - looks a lot better - and some way for them not to decohere will be required - but they are isolated so some way can probably be found - we will assume for the sake of argument it has.

    I am inclined to agree with MFB - it becomes: |ψ> = |calculated, now dead δ>|uncalculating β> + |uncalculating (still dead if battery was used) δ>| calculating β>.

    Systems change state all the time - nothing startling here.

    Thanks
    Bill
     
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