On Tuesday, May 22, 2018 at 10:06:39 PM UTC, Brent wrote: > > > > On 5/22/2018 6:39 AM, [email protected] <javascript:> 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 > > 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}}} [image: {\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. > > Brent >
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