On 29 Nov 2017, at 23:16, Bruce Kellett wrote:
On 30/11/2017 2:24 am, Bruno Marchal wrote:
On 29 Nov 2017, at 04:59, Bruce Kellett wrote:
I would suggest that there is no such world. Whether a coin comes
up head or tails on a simple toss is not a quantum event; it is
determined by quite classical laws of physics governing initial
conditions, air currents and the like.
It depends. If you shake the coin long enough, the quantum
uncertainties can add up to the point that the toss is a quantum
event. With some student we have evaluate this quantitavely (a long
time ago) and get that if was enough to shake the coin less than a
minute, but more than few seconds ... (Nothing rigorous).
That is a misunderstanding of quantum randomness. For the outcome of
a coin toss to be determined by quantum randomness, we would have to
have a single quantum event where the outcome was amplified by
decoherence so that it was directly entangled with the way the coin
landed. Schematically:
|quantum event>|coin> = (|outcome A> + |outcome B>)|coin>
= (|outcome A>|coin heads> + |outcome B>|coin tails>)
The coin is quantum. The quantum event is given by its position, the
Heisenberg uncertainty makes it diffusing rapidly (at the speed of
light) and decoherence is only local contamination of the
superposition of the "gaussian" position, this evolves in infinity of
(gigantic number of universe) with the coin landing on tail or head
about one halve the contexts.
This direct entanglement is not reproduced by the sum over many
random quantum events where the ensuing entanglement is extremely
complicated, with no direct connection between a quantum outcome and
the result of the toss.
Why? It looks you make QM wrong for the coin.
Such accumulation of quantum uncertainties is similar to simple
thermal noise, and could not be distinguished from it.
I agree. In no worlds there will be able to distinguish the MW from
some UM, but that was not the point. Yet, it seems to me that with the
quantum (the real) coin, the Heisenberg uncertainties on the position
grows with shaking leading after some times to an infinity of
universes, having different results, but with the right classical
statistics (1/2). It is just that decoherence is almost at speed c
that at no time we can detect intermediate interference, and then, as
usual, we don't feel the split.
Bruno
Bruce
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