Lev Vaidman

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  • #3265
    Lev Vaidman
    Participant

    I thank Aurelien for citing my works, but his acknowledgement to me at the end of his paper is misleading. Although I tried to explain my views to him in a couple of e-mails, I failed. Reading his presentation of my views I could not recognize them at all. I disagree with everything I saw in Aurelien paper.
    Lev Vaidman

    #2790
    Lev Vaidman
    Participant

    Exactly. I am aware that the founders of GRWm view it differently and in the paper you mentioned it is claimed that S0 and Sm are different, but I do not see it. The only ontology is the wave function. “m” is an emergent property which help us to understand world around us. If we want to add to physics ontology of the Universe our world ontology, “m” will be there.

    #2780
    Lev Vaidman
    Participant

    First, I did not say local, I said that MWI has no action at a distance. The (nonlocal) connections you talk about are changed locally.
    Operators are very far from reality. Ontology is the wave function, quantum states, not values of observables. According to my picture in your language tables are as GRW-m, only there are no collapses and density measured inside a “world” which is a vague concept which has to be carefully explained. These are LOCAL properties of the Wave Function.

    #2776
    Lev Vaidman
    Participant

    Dear Travis,

    Yes, you are on the right track. Locally, there is only local density matrix. It captures all information about what is there. And it cannot be changed by action at a distance.
    But, all local density matrices do not exhaust all the ontology. Wave function is more than this. And in some sense it is non-local (entanglement etc.). However, local density matrix is certainly real as it ALL what is in a particular location. If something in this location entangled with something in other location, local interaction might lead to entanglement to more systems, but no change happens nonlocally: no action at a distance!
    I am preparing a talk “Ontology of the wave function”, Saig, July 22. If it will be recorded in some way I’ll send you a link.

    #2770
    Lev Vaidman
    Participant

    Dear Travis,

    I am ready for your semantics about beables.

    About action at a distance. When I deal with a physical theory I assume a closed system and an external omnipotent creature which can test the theory making disturbances and observation of what is going on that system. So there is no issue of “free will”.

    Nonlocality of Bohm is best manifested in its treatment of the EPR-Bohm system of two separated particles in a singlet state. If Bohmian position of the two particles in the EPR pair are in their upper half, then measuring spin of one particle will change the result of spin measurement of other particle immediately after.

    In contrast, any local action in one place will cause no change in the complete local description (local density matrix) of other place. I describe it in detail in Quantum Theory and Determinism, L. Vaidman, Quantum Stud.: Math. Found. 1, 5-38 (2014) quant-ph 1405.4222.

    #2759
    Lev Vaidman
    Participant

    Dear Aurelien,

    Yes, there are many interesting subtle effects when the experiment involves entanglement. But my current simple proposal including introducing the beam splitter for coherent quantum signal does not involve entanglement. ALL particles Alice detects had no Bohmian trajectories passing through Bob’s site.

    #2744
    Lev Vaidman
    Participant

    Dear Travis,

    Thank You for the post. I think I agree with what you write, although I do not feel particular need for beables and for me wave function is ontology and the only ontology. I agree that MWI requires much more to explain our experience than Bohm, but the advantages of the MWI as a physical theory (no action at a distance, more economical in concepts) put it for me far beyond any competition.

    #2732
    Lev Vaidman
    Participant

    Dear Aurelian,

    Thank You for the Comment. But why you say that Bob cannot superpose the message in a coherent way? He should put in the location 1 of the mirror, a 50:50 beam splitter instead, and a permanent mirror at location 2. This provides a coherent superposition of messages 1 and 2. Alice can arrange interference between them and measure the phase which Bob fixes. This modification is “Bohmian counterfactual” as well.

    #2731
    Lev Vaidman
    Participant

    Dear Travis,
    Of course, communication with a water wave, or with a classical electromagnetic wave is not counterfactual. What I felt is that some Bohmians do not take quantum wave, and especially empty wave, in a strong ontological sense. Sometimes, wave is considered as a part of a physical law which governs the particle motion. My guiding principle of the presence of a particle in a particular place is the (weak) trace it leaves there. Empty Bohmian waves sometimes leave trace, and this is the case in the setup I proposed, so from my point of view is is not counterfactual.

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