Russell Standish wrote:
>
>Also note that exact measurements of microstates is *in principle*
>incompatible with the Heisenberg Uncertainty Principle.

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Well, that's why I defined microstates as "detailed descriptions of the
positions and momenta of all the particles, within the limits of the
uncertainty principle". My memory is that in the quantum version of
statistical mechanics, the phase space is partititioned into finite regions
so that the uncertainty principle does not prevent you from measuring which
region the system is in (and the regions are made as small as possible while
still having that be true). I wonder if there'd be a natural way to look at
statistical mechanics in the MWI interpretation though--I would think the
maximal information about a system, analogous to the "microstate", would be
the system's exact quantum state (which only assigns amplitudes to different
values of noncommuting variables like position and momentum), and the
evolution of the system's quantum state over time should be completely
deterministic, and also "information-preserving" in the sense that knowing
the quantum state at a later time would tell you the quantum state at an
earlier time. But I can't think what "macrostates" you'd use, since a
particular quantum state can involve a superposition of different possible
temperatures, pressures and so forth.
Jesse
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