On 5/22/2018 6:55 PM, [email protected] wrote:
On Wednesday, May 23, 2018 at 1:45:39 AM UTC, Brent wrote: On 5/22/2018 5:59 PM, [email protected] <javascript:> wrote:On Wednesday, May 23, 2018 at 12:44:06 AM UTC, Brent wrote: On 5/22/2018 3:46 PM, [email protected] wrote:On Tuesday, May 22, 2018 at 10:41:11 PM UTC, [email protected] wrote: On Tuesday, May 22, 2018 at 10:06:39 PM UTC, Brent wrote: On 5/22/2018 6:39 AM, [email protected] wrote:I'm OK with getting rid of the projection operator. Are you now claiming information is lost or inaccessible in these orthogonal subspaces and therefore quantum measurements cannot be reversed?They are inaccessible to the people of any one world of the MWI. No! Irreversible FAPP! Think heat bath or Bucky Balls. https://en.wikipedia.org/wiki/Quantum_decoherence <https://en.wikipedia.org/wiki/Quantum_decoherence> Examples of non-unitary modelling of decoherence Decoherence <https://en.wikipedia.org/wiki/Decoherence> can be modelled as a non-unitary <https://en.wikipedia.org/wiki/Unitary_operator> process by which a system couples with its environment (although the combined system plus environment evolves in a unitary fashion).^[4] <https://en.wikipedia.org/wiki/Quantum_decoherence#cite_note-Lidar_and_Whaley-4> Thus the dynamics of the system alone, treated in isolation, are non-unitary and, as such, are represented by irreversible transformations <https://en.wikipedia.org/wiki/Irreversibility> acting on the system's Hilbert space <https://en.wikipedia.org/wiki/Hilbert_space>, H {\displaystyle {\mathcal {H}}} {\mathcal {H}}. Since the system's dynamics are represented by irreversible representations, then any information present in the quantum system can be lost to the environment or heat bath <https://en.wikipedia.org/wiki/Heat_bath>. Alternatively, the decay of quantum information caused by the coupling of the system to the environment is referred to as decoherence.^[3] <https://en.wikipedia.org/wiki/Quantum_decoherence#cite_note-Bacon-3> Thus decoherence is the process by which information of a quantum system is altered by the system's interaction with its environment (which form a closed system), hence creating an entanglement <https://en.wikipedia.org/wiki/Quantum_entanglement> between the system and heat bath (environment). As such, since the system is entangled with its environment in some unknown way, a description of the system by itself cannot be made without also referring to the environment (i.e. without also describing the state of the environment).Notice that this doesn't explain how one gets to a single result. I did, but you're avoiding the key point; if the theory is on the right track, and I think it is, quantum measurements are irreversible FAPP. The superposition is converted into mixed states, no interference, and no need for the MWI.You're still not paying attention to the problem. First, the superposition is never converted into mixed states. It /approximates/, FAPP, a mixed state/in some pointer/ basis (and not in others). Second, even when you trace over the environmental terms to make the cross terms practically zero (a mathematical, not physical, process) you are left with different outcomes with different probabilities. CI then just says one of them happens. But when did it happen?...when you did the trace operation on the density matrix? I think the main takeaway from decoherence is that information isn't lost to other worlds, but to the environment in THIS world.But that ignores part of the story. The information that is lost to the environment is different depending on what the result is. So if by some magic you could reverse your world after seeing the result you couldn't get back to the initial state because you could not also reverse the "other worlds".What "other worlds"? If they don't exist, why should I be concerned about them? AG
That's pretty much the CI attitude and that of most working physicists. But those interested in fundamental questions would still like to pin down the time and how of the process of branching and especially how the classical world arises from this process. Metaphysicians like Bruno want to use a kind of implied "everythingism" to simplify their overarching theory of the world by saying that "everything happens"...just somewhere else. If you say only your world exists then you are committed to an inherent randomness in the world...some find that anathema.
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