On 5/12/2017 3:39 am, Bruno Marchal wrote:
On 04 Dec 2017, at 05:17, Bruce Kellett wrote:
On 4/12/2017 2:34 pm, Russell Standish wrote:
On Mon, Dec 04, 2017 at 02:11:11PM +1100, Bruce Kellett wrote:
On 3/12/2017 9:03 am, Russell Standish wrote:
The point being that the uncertainty in the coin's initial position is
itself due to the amplification of quantum uncertainty by classical
chaos.
That may happen in some cases, but just looking at the numbers says that
normal thermal motions will far outweigh the effect of any residual quantum
uncertainty. In most cases where the Lyanpunov exponents lead to classical
chaos, there is more than enough classical thermal uncertainty in the
initial conditions so that any residual quantum uncertainty is irrelevant.
But surely, classical thermal uncertainty is just due to amplification
of quantum uncertainty by means of molecular chaos.
But molecular chaos, /a là/ Eherenfest, Maxwell, Boltzmann /et al./
is essentially a classical phenomenon, due to the random motions of
atoms or molecules in the kinetic theory. Although these are, in
some sense, quantum objects, the momenta involved at normal
temperatures are such the uncertainty principle considerations are
irrelevant.
Yes, but only FAPP (For All _Practical _Purposes)
You use FAPP as a convenient escape from the realities of the situation.
Sure, in pure unitary SWE evolution, the worlds that form are only FAPP.
But that does not mean that you can use the original superposition for
any purposes whatsoever, practical or impractical. FAPP means that there
is no practical way that you can reconstruct the original superposition,
or interact with the other worlds.
We already know in this case that from the 1p perspective, nothing
change, but the point is that the whole picture remains (described by)
a pure state.
So what? That is purely a theoretical construct, of no practical
importance, as you point out above. When you are considering coin tosses
or molecular chaos, the purely classical description is completely
adequate, whether you want to consider it FAPP or not.
So there is no quantum uncertainty involved in standard molecular
chaos, or in the random thermal motion of molecules in liquids or gasses.
Then you introduce a collapse somewhere.
No collapse anywhere. If you think there is, then point it out!
I am not sure I can make sense of you call "classical", here.
I think that the sense of "classical" is completely clear. It is what
emerges from the quantum when quantum uncertainties and superpositions
are no longer relevant (FAPP or not, the point is that such things are
not relevant).
Do you not understand that one of the enduring mysteries of quantum
theory is the emergence of the classical world from the purely quantum
substrate? Decoherence goes a long way towards answering the underlying
problems, but unless something intervenes to exactly zero the
off-diagonal terms in the density matrix, the the understanding that we
have is still only FAPP. But the emphasis here is on *Practical*,
rabbiting on about the multiverse is not in the least practical, here or
anywhere else.
Bruce
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