On 11-12-2017 00:55, Bruce Kellett wrote:
On 10/12/2017 11:06 pm, smitra wrote:
On 09-12-2017 21:12, Brent Meeker wrote:
On 12/9/2017 2:36 AM, smitra wrote:
Yes, it's a different argument but it's also generically correct.
But I do think for the discussions in this list it doesn't matter
all that much whether an initial single branch will diverge into
multiple branches due to effectively classical dynamics.
Branching due to effectively classical dynamics is a contradiction in
terms. If it's effectively classical it can't branch.
Counterexample: A perfectly balanced pencil on its one atom wide tip.
Good luck trying to balance anything on a single atom - thermal
fluctuations make it impossible.
A variant of this involving longer time scales is a rectangular block
that's standing on the floor. Due to quantum tunneling it will
eventually tip over.
Quantum tunnelling???? What is tunnelling through what potential
barrier?
The time scale depends on the width and height. Suppose that we keep
the height at 10 cm, but make the width very small but still much
larger than the size of an atom, such that the block will fall on time
scales of the order of 10^18 years.
Where did that figure come from? The current age of the universe is
only of the order of 10^10 years. And even on that timescale, thermal
fluctuations will reduce the block to rubble.
If we cover the surface of a Mars-sized planet with such blocks placed
one centimeter apart, then we need about 1.4 10^18 blocks. If one
block falls, then it will trigger the next block to fall and
eventually all the blocks will fall. So, the blocks will start to fall
within a time scale of just a year, and we can observe this from a
satellite orbiting Mars.
So, even though everything looks like in the classical domain FAPP,
the time scale of 10^18 years on which quantum tunneling occurs looks
like infinity FAPP, you'll still have a splitting in the MWI view of
how the blocks will fall within just a year.
Thermal fluctuations will do it in less than a year.
Objections like that thermal fluctuations dominate quantum
fluctuations can be easily address by imagining cooling down the
entire planet to sufficiently low temperatures. Compared to the
falling pencil, this example is a more robust against such objections,
e.g. a single photon colliding with the pencil would already cause it
to tip over, but it won't cause a block to tip over.
Why would I want to cool the planet down? Even at absolute zero there
are still thermal fluctuations -- not everything comes to rest at 0 K.
What you have to do if you want to claim that all chance outcomes are
of quantum origin is compare the relative magnitudes of quantum and
thermal fluctuations at room temperature -- room temperature because
that is where we do the experiments. And you haven't done that;
neither has Albrecht in the paper you reference. That is why his paper
is a load of nonsense.
Thermal fluctuations do not need to be eliminated, as they are of pure
quantum mechanical origin. However, if one has to argue about that then
one loses the point of the proposed experiment. At absolute zero the
thermal fluctuations are due to zero point motion, take e.g. the
harmonic oscillator which then has an energy of 1/2 hbar omega.
In generic non-integrable systems you'll have chaotic behavior where
small perturbations grow exponentially. Thermal fluctuations will then
originate from quantum fluctuations.
Saibal
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