On 06 Dec 2017, at 12:19, Bruce Kellett wrote:
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?
That does not follow.
You need to prevent the relative decoherence, which is very hard with
usual temperature and macroscopic bodies.
Quantum coherence can never be lost? You are talking nonsense.
It is never loss in the "bird picture". It is always lost in the
picture of whoever interact with the system observed.
Decoherence and the associated loss of coherence is universal since
protection from interaction with the environment is very hard to
achieve.
Right. But the loss of coherence is only a point of view of an
observer who entangled itself with the system under observation.
You are not going to recover it for a particular object with a bit
of shaking.
Nobody claimed that.
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.
You can add some other dynamic, but you get non-locality,
indeterminacy, etc.
But that is not the point. You make the coin toss in a particular
world --
That never happens. As far as the coin is localized (not sharply),
there is a range of uncertainties in the momentum, and vice versa:
there are always a lot of coins, perhaps an infinity.
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.
FAPP only.
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.
I doubt this. In a world with the coin here, it might bounce on the
left, and in a world where the coin is a nano millimeter away, it can
bounce of the right. very small difference of the position of the coin
can be naturally amplified by the shape of the box used for the
shaking, and the chaotic nature of the shaking.
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.
? A position is a superposition of different momenta, and vice versa.
That is basic QM.
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.
You seem to work in Bohr QM, with some dualism between the quantum
reality and the classical reality.
You are right that this does not change anything FAPP, but our
discussion is not about practical applications, but metaphysics.
Bruno
Bruce
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