On 12/3/2018 8:50 AM, Bruno Marchal wrote:
On 3 Dec 2018, at 10:35, Philip Thrift <cloudver...@gmail.com
<mailto:cloudver...@gmail.com>> wrote:
On Sunday, December 2, 2018 at 8:17:54 PM UTC-6, Brent wrote:
On 12/2/2018 5:14 PM, Philip Thrift wrote:
On Sunday, December 2, 2018 at 4:25:04 PM UTC-6, Brent wrote:
On 12/2/2018 11:42 AM, Philip Thrift wrote:
On Sunday, December 2, 2018 at 8:13:48 AM UTC-6,
agrays...@gmail.com wrote:
*
*
*Obviously, from a one-world perspective, only one
history survives for a single trial. But to even
grossly approach anything describable as "Darwinian",
you have to identify characteristics of histories which
contribute positively or negatively wrt surviving but I
don't see an inkling of that. IMO, Quantum Darwinism is
at best a vacuous restatement of the measurement
problemt; that we don't know why we get what we get. AG*
In the *sum over histories* interpretation - of the
double-slit experiment, for example - each history carries
a unit complex number - like a gene - and this gene
reenforces (positively) or interferes (negatively) with
other history's genes in the sum.
But I thought you said the ontology was that only one
history "popped out of the Lottery machine"? Here you seem
to contemplate an ensemble of histories, all those ending at
the given spot, as being real.
Brent
All are real until all but one dies.
RIP: All those losing histories.
The trouble with that is the Born probability doesn't apply to
histories, it applies to results. So your theory says nothing
about the probability of the fundamental ontologies.
Brent
The probability distribution on the space of histories is provided by
the path integral.
Except that isn't true. A probability (or probability density) is
provided for a bundle of histories joining two events. It doesn't not
provide a probability of a single history.
Brent
I agree, and this statement can be made rather rigorously in the
approach of Griffith and Omnes, except that Omnes eventually add an
axiom of irrationality to extract a unique physical reality from the
formalism. He said it, at least, explicitly: like saying “and now
there is a miracle”. He says that at this stage, we need
irrationalism. But that appears in the last ten sentences of a rather
quite rational book.
Well, the point is that we can generalise the Born rule for making
sense on some probabilities on "consistent histories”.
(But I am in trouble (now) on how to handle the GHZ state in term of
(Griffith and Omnes)-histories (3-particle-GHZ = 1/sqrt(2)(up up up +
down down down)).
*Backward causation, hidden variables and the meaning of completenes*s
[ https://www.ias.ac.in/article/fulltext/pram/056/02-03/0199-0209 ]
/Feynman’s path integral approach, calculation of the probability of
the outcome in question depends on an integration over the possible
individual paths between the given initial state and the given final
state, each weighted by a complex number. The fact that the weights
associated with individual paths are complex makes it impossible to
interpret them as real valued probabilities, associated with a
classical statistical distribution of possibilities./
/
/
/However, there is no such difficulty at the level of the entire
‘bundle’ of paths which comprise the path integral. If we think of
the hidden reality as the instantiation not of one path rather than
another but of one entire bundle rather than another, then the
quantum mechanical probabilities can be thought of as classical
probability distributions over such elements of reality. (For
example, suppose we specify the boundary conditions in terms of the
electron source, the fact that two slits are open, and the fact that
a detector screen is present at a certain distance on the opposite
side of the central screen. We then partition the detector screen, so
as to define possible outcomes for the experiment. For each element
O_i of this partition, there is a bundle B_i of Feynman paths,
constituting the path integral used in calculating the probability of
outcome O_i . We have a classical probability distribution/
/over the set of such B_i ./
One could stop at /history bundles/ as the sample space, or the
"hidden reality" could be that /one history/ is selected at random
from the history bundle. That could occur with t*ime symmetry*
(retrocausality): The one path is chosen at random from a history
bundle at the source in the present from the distribution determined
on the history bundles in the future.
With mechanism, the randomness and the unicity is a first person
(plural) experience only, and seems to me no more astonishing than in
the amoeba duplication, or than in the Helsinki—> Washington/Moscow
duplication, as seen from the first person ways.
Bruno
- pt
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