On 2/7/2020 5:57 PM, Bruce Kellett wrote:
On Sat, Feb 8, 2020 at 12:28 PM Lawrence Crowell
<[email protected]
<mailto:[email protected]>> wrote:
On Friday, February 7, 2020 at 7:10:54 PM UTC-6, Bruce wrote:
On Sat, Feb 8, 2020 at 11:51 AM Lawrence Crowell
<[email protected]> wrote:
On Friday, February 7, 2020 at 6:16:45 PM UTC-6, Bruce wrote:
On Sat, Feb 8, 2020 at 4:33 AM Stathis Papaioannou
<[email protected]> wrote:
On Fri, 7 Feb 2020 at 15:59, Bruce Kellett
<[email protected]> wrote:
This argument from Kent completely destroys
Everett's attempt to derive the Born rule from
his many-worlds approach to quantum mechanics.
In fact, it totally undermines most attempts
to derive the Born rule from any branching
theory, and undermines attempts to justify
ignoring branches on which the Born rule
weights are disconfirmed. In the many-worlds
case, recall, all observers are aware that
other observers with other data must exist,
but each is led to construct a spurious
measure of importance that favours their own
observations against the others', and this
leads to an obvious absurdity. In the
one-world case, observers treat what actually
happened as important, and ignore what didn't
happen: this doesn't lead to the same difficulty.
Carroll and Sebens worked a paper a year ago illustrating
how MWI was consistent with Born rule. They did have to
restrict paths or states that were too far removed from
being a good Bayeisan prior, so it is a bit loose.
However, it was not bad.
Not bad!!!! I suppose if you feel justified in just throwing
away anything that does not suit your favourite theory, then
you can get away with anything. It is the fact that these
'worlds' that are far removed from what one wants to see
cannot just be "thrown away" that destroys MWI. Given that the
probability of particular outcomes no longer has meaning when
all outcomes necessarily occur, one cannot use any observed
data to justify any theory about the probabilities. All
theories are just as good, or just as bad. Consequently,
assuming probabilities for particular outcomes no longer makes
any sense.
The set of amplitudes or paths thrown away is a small measure. The
bounds are not entirely certain, but they are comparatively small.
The problem is to justify that the paths thrown away do, in fact, have
small measure. The proof given by Kent shows that, whatever result you
obtain, you can argue that contrary results have "small measure", and
can be thrown away.
But that is answering the inverse problem. It's showing that there are
experimenters who will verify wrong theories and would throw away many
values in the MWI from the God's eye view. But they don't know of those
values. The point is that the experimenters who do this and accept the
wrong theory are small in number. So we may rationally expect to be
among those who are right.
There is nothing that picks out one particular set of paths as
preferred in the many-worlds situation.
Sure you can. For example you can pick out the set of paths whose
statistics are within some bounds of the mean.
One can only get that in a stochastic one-world model.
All paths occur in a stochastic one-world model too. The only
difference is that some probability measure is assumed as part of the model.
Brent
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