Why the "Many-Worlds" Theory doesn't make sense...

Discussion in 'Physics & Math' started by stateofmind, Feb 12, 2015.

  1. PhysBang Valued Senior Member

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    You imagine that Many Worlds theorists ignore the consequences of their theory. The best do not; they just do not find the consequences to be something that should be viewed negatively. You offered no reason to suppose that the consequences were negative, so you were just attacking their character.

    I don't like the Many Worlds interpretation, but I don't just attack the character of those who believe it.
     
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  3. QuarkHead Remedial Math Student Valued Senior Member

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    You know, before dismissing an interpretationof a theory as "garbage" it would be as well to understand the theory itself
    This is a case in point.The wavefunction describes the state of a quantum system. The observables i.e. those properties of the system potentially capable of being measured, are given by operators acting on the state (which is a vector)

    And the actual measurements on this state are given by the eigenvalues for these operators. It is true that in QM the set of all eigenvalues for a given operator may have a continuous spectrum, but so what? Ah, here's what
    If this comment has any meaning at all - which I doubt - reflect on this...... The operators I mentioned above are essentially by definition Hermitian. This means their eigenvalues are all Real. Even though the Real Numbers are Gauchy complete i.e. there are no "gaps", I at least have no difficulty, philosophical or otherwise, in using them to measure things

    Anyway, it seems to me - though I am not a physicist - that the original question is poorly posed, so let's drop all mention of "worlds" and "universes" (as they carry linguistic baggage)....

    Suppose a quantum system, say a 1 particle system, in a certain sate \(S\). Theory says that this state is in general the superposition of other states, say \(S = A+B\). Further suppose a measurement on state \(A\) is definitely \(a\) and that on state \(B\) is definitely \(b\) then a measurement on \(S\) will be definitely either \(a\) or \(b\) (perhaps weighted in some way)

    So, having obtained one of these definite measurements for \(S\), what are we to say about the superposition?

    1. We were wrong - there was originally no superposition?

    2. Yes there was superposition before measurement but there no longer is afterwards?

    3. By making a single measurement one has simply accessed only one of 2 co-existing quantum realities?
     
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  5. RJBeery Natural Philosopher Valued Senior Member

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    So a mathematician has no problem with the mathematical description of physics. That's surprising?

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    How "many" potential Eigenvalues are in a continuous spectrum for a given operator? Because my objection was that MWI demands a continuous stream of an infinite number of worlds and your response seems to be that I didn't understand MWI...but then you seem to agree with the validity of my objection, but not my philosophical problem with it.

    #2 is "the measurement problem". What constitutes a measurement? This is fraught with issues.

    #3 is MWI simplified to the binary choice of A and B. As I mentioned earlier, digital quantum outcomes are actually the exception to the rule; the wavefunction is generally continuous.

    #1 is my vote, and I have plenty of reasoning for it but this isn't really the venue to share.
     
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  7. QuarkHead Remedial Math Student Valued Senior Member

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    Uncountably many. Consider the eigenvalues for the position or momentum operators acting on a single state vector

    This was my rather clumsy description of the so-called Copenhagen Interpretation.

    So you don't see the value of simplifying a problem to make a general point?
    Well it is always continuous in that it takes on values in \([-1,1]\)

    But you missed the point I was at pains to make - you are not measuring the wavefunction, you are determining the eigenvalues for an operator acting upon it

    So you deny that a general quantum state is the superposition of other states? Experiments - many of them - show you are just plain wrong, let alone the theory
     
    Last edited: Mar 2, 2015
  8. RJBeery Natural Philosopher Valued Senior Member

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    Agreed, an infinite number. This does not settle well with me.
    When we measure spin, for example, we don't declare to be "determining the eigenvalue for the operator acting upon the wavefunction...", we just say we are measuring the spin. Not only is this pure semantics, I'm apparently still missing the point you were at pains to make.
    Yes I do! In my opinion the superposition of states is epistemological in nature and has no physical manifestation whatsoever.
     
  9. QuarkHead Remedial Math Student Valued Senior Member

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    The "we" being whom? You and your colleagues in your experimental physics lab?

    Look, I am not the right person to teach you quantum theory. But I am allowed to ask the question:When you and your colleagues are "measuring spin", are you measuring the spin of the wavefunction associated to a quantum entity? Recall that there is one and only one wavefunction/state function associated to each quantum entity

    Recall also that this state function is an element in an Hilbert space of square integrable functions aka a vector space and is therefore aptly described as a state vector.

    Functions do not spin. Vectors do not spin, so what do you and your colleagues measure?
    I have no idea what this means (and I do not wish to know, thanks all the same)
     
  10. RJBeery Natural Philosopher Valued Senior Member

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    Your use of language makes many presumptions, such as the physicality of the math involved (the map is not necessarily the territory) and a curious insinuation that I don't understand MWI.

    When a physicist measures spin he need not concern himself with your wavefunction associated to the quantum entity; he just measures the spin of the particle under consideration. Your (purely mathematical) description of what's going does not dictate nor even resemble reality any more than claiming that the top card in a deck of cards is "1/52 of an Ace of Spades" until we turn it over.

    Now it should be clear what I meant about "epistemological": it means that a superposition of quantum states is not physical in any way, but rather related to what we know about the system.
     
  11. phyti Registered Senior Member

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    I agree with RJB. Someone has to inject some reasoning into scientific thinking, so as to distinguish between theory and physical phenomena/reality. Theoretical transactions are done on paper or a computer. They only correspond/represent unknown entities involved in reality. No one sees arrows attached to objects in motion, or trajectories, orbits, etc. Mathematical expressions are a simplistic and abstract method of behavioral science for the world we inhabit. An array of gremlins throughout the universe would work just as well as Hamiltonians, tensors, curvelinear coordinates, etc. All concepts are abstract since that is what the mind produces, in an effort to understand/comprehend it's environment.
    When considering superposition of states, why not just say " I don't know".

    If the census claims there are 2.3 children per household, find an address, so I can visit and see the mutant.
     
    Last edited: Mar 2, 2015
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  12. RJBeery Natural Philosopher Valued Senior Member

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  13. brucep Valued Senior Member

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    What does a theory do? It makes predictions associated with real natural phenomena. Then we can use empirical methods to test theoretical predictions about real natural phenomena. They're forever married.
     
  14. PhysBang Valued Senior Member

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    No, that is impossible.

    There is no "spin" without the quantum theory. There are a host of physical behaviors that one can measure, but one cannot identify them with spin unless one is using the theory.

    The many world interpretation says that superposition states evolve into superposition states. When we appear to observe only the behavior associated with one of the states in the superposition, that is part of (the physical system which is) our mind interacting with that part of the superposition; presumably our mind is now also in a superposition with the other states involved.

    I don't like it, just like I don't like the idea that the universe is in some sort of branching infinite superposition. But not liking something is not enough to reject it as an option. Fortunately, nothing in the physics seems to force this interpretation over any other, so I don't let it worry me.
     
  15. RJBeery Natural Philosopher Valued Senior Member

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    PhysBang I think you need to read the context of my comment. QuarkHead is assigning physical significance to the wavefunction. We are certainly free to do this just as we are free to claim that an unknown card is 1/52 of an Ace of Spades until we turn it over; mathematically this description is valid. What I said is that we NEED not concern ourselves with the wavefunction itself, we are still free to make measurements without it.

    I'm not questioning the utility of the math, I'm questioning the physical significance of it. This is not the same thing as rejecting MWI as an option; a valid interpretation cannot be objectively refuted. I'm claiming that, aesthetically and philosophically, MWI is garbage.
     
  16. QuarkHead Remedial Math Student Valued Senior Member

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    Yes, I apologize for my "insinuation".

    So let me be more clear: Anyone who rejects the principle of superposition does not understand Quantum Mechanics.

    Anyone who does not understand Quantum Mechanics cannot possibly understand its various interpretations.

    See, no "insinuations" there
     
  17. RJBeery Natural Philosopher Valued Senior Member

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    If you're demanding physical significance of the principle of superposition then you are flatly rejecting other valid interpretations (such as Feynman's Absorber Theory). Flatly rejecting ANY valid interpretation is evidence that one does not understand QM or the definition of an interpretation. As I've stated many times my objection with MWI is aesthetic and philosophical, not technical.
     
  18. QuarkHead Remedial Math Student Valued Senior Member

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    Oh right, whatever
     
  19. brucep Valued Senior Member

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    The interpretations intend to be pedagogical. They're a teaching tool. If you're working with quantum mechanics you probably don't give a crap about contrived explanations for how the theory works. Who gives a crap about some cranks preferred contrived explanation for quantum mechanics. The guy you're talking to thinks the Schwarzschild bookkeeper coordinates are preferred. For cranks the choice is ignorance.
     
  20. RJBeery Natural Philosopher Valued Senior Member

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    The importance of relating the mathematical theories to the physical world only fell out of favor when QM made things difficult. "Shut up and calculate" became popular because we're still struggling to explain things, not because an acceptable interpretation is not relevant. I'm not sure why some tepid old intellect feels that he speaks for the Physics community anyway...
     
  21. brucep Valued Senior Member

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    So put a cork in it pretender.
     
  22. Farsight

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    It always makes my laugh at how charlatans and quacks who peddle garbage like the multiverse are so hostile to bona-fide sincere people. They have to be, because the trash they're pushing doesn't stand up to scrutiny, and nor do they.
     
  23. PhysBang Valued Senior Member

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    Farsight, you are a liar, not a sincere person. You have lied many times on many places on the internet. You lie to defend your scientific position based on two quotations from Einstein and zero ability to do any of the science that Einstein (and others) created. You regularly insult the real scientists who take the time to learn science.

    In this case, you insult the people that propose the many worlds interpretation without the ability to understand what the interpretation actually says. You insult it because you think that it is an easy target and that it will make you look more intelligent. Your ability to insult does not make you look more intelligent. Your lies do not stop you from looking foolish. Your dogmatic, quasi-religious pseudo-scientific views do not look reasonable.
     
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