On 05 Dec 2017, at 01:48, Bruce Kellett wrote:
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.
Apparently not, given that in one case shaking the coin long enough
brings the existence of quasi othogonal realities with the coin on
each side, and this despite we cannot detect them in any sensible way.
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!
Well, if the uncertainties of the coin position is amplified by the
quasi-classical chaotic motion due to the shaking, I don't see how the
resulting wave can make the other branches disappearing.
My only doubt on this comes from the fact that due to the linearity,
the starting error does not grow up enough for the outcomes to be ever
different, but they don't need to grow up, in fact, if we have still
anything resembling to the "classical" indeterminacy.
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).
But then we agree. I was not talking on anything FAPP, here, but on
the existence of inaccessible, but physically real alternate branch.
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.
Then we were not discussing the same thing.
Bruno
Bruce
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