On 6/12/2017 9:54 pm, Bruno Marchal wrote:
On 05 Dec 2017, at 01:26, Bruce Kellett wrote:
On 5/12/2017 3:15 am, Bruno Marchal wrote:
I think that is enough to get the macroscopic superposition, as,
like I explained, you have to take into account not just the quantum
indeterminacy, + the classical chaos. You might need to shake for
some minutes.
You could shake for longer than the age of the universe and you will
still not convert quantum uncertainties and classical thermal motions
into a macroscopic superposition. Do you know nothing about
coherence? And the fact that coherent phases between the components
are what separates a superposition from a mixture? Random quantum
uncertainties and thermal motions are not coherent, so cannot form
superpositions.
Not coherent can only be a relative point of view brought by the first
person indeterminacy. In the 3p perspective coherence never disappear,
and once a particle is in a superposition state, it remains so forever
(in QM without collapse).
So quantum computing is a cinch because everything is always coherent?
Quantum coherence can never be lost? You are talking nonsense.
Decoherence and the associated loss of coherence is universal since
protection from interaction with the environment is very hard to
achieve. You are not going to recover it for a particular object with a
bit of shaking.
Look at Everett's explanation of why coherence explains the appearance
of decoherence and collapse.
You just assume collapse. You assume the SWE is wrong somewhere. Where?
Collapse does not necessarily mean that the SWE is wrong -- it could
come from some other dynamics. But that is not the point. You make the
coin toss in a particular world -- there might be an indefinite number
of other worlds with coin tosses, but they do not affect the result of
your toss (the 1p view). The 3p (bird) view is absolutely irrelevant to
the outcome of any particular toss. You just confuse yourself by
thinking that such things make a difference.
That is why quantum uncertainties are irrelevant for macroscopic
objects. Uncertainties do not add up coherently for macroscopic
objects --
Sure they do, unless you add continuous collapse, or something.
decoherence is only entanglement with the environment, that is
"contagion of the superposition".
You are talking rubbish. As above, the uncertainties are not coherent
They look that way, but it is only because we get eventually entangled
with the coin (here).
We are already entangled with the coin, but the fact that the
uncertainties involved in the toss are all purely classical and due to
our ignorance of the initial conditions, the outcome is classically
determined, and there is only one outcome for any toss -- no splitting.
so they cannot add up to form a superposition.
The heisenberg uncertainty is due to a superposition existing at the
start.
You couldn't be more wrong if you tried.
Collapse has nothing to do with it. Decoherence is unitary
interaction with the environment, so that the environment becomes
entangled with the original superposition, but you have to start with
a superposition -- that process does not make one!
It starts with one. Any position and momentum are superposition of
each other. They behave as gaussian packet, each being a Fourier
transform of the other.
Perhaps it is just your difficulties with the English language, but this
is hopelessly confused. The HUP means that an isolated particle cannot
be in a simultaneous eigenstate of both position and momentum, so it is
generally found in the form of a wave packet, in which there is a
superposition of say momentum eigenstates, or, equivalently, of position
eigenstates. These superpositions are related by a Fourier transform,
but there is no reason why the wave packet should be a gaussian. But
whatever you say about wave packets, position and momentum are not
superpositions of each other.
But as I pointed out, thermal motion gives momenta of magnitudes such
that the quantum uncertainties are negligible compared to the thermal
randomness. And thermal motions are not coherent.
Bruce
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