On 14 Jul 2016, at 02:11, Bruce Kellett wrote:
On 13/07/2016 11:36 pm, Bruno Marchal wrote:
On 11 Jul 2016, at 13:49, Bruce Kellett wrote:
On 11/07/2016 9:31 pm, Bruno Marchal wrote:
Holiday Exercise:
A guy undergoes the Washington Moscow duplication, starting again
from Helsinki.
Then in Moscow, but not in Washington, he (the one in Moscow of
course) undergoes a similar Sidney-Beijing duplication.
I write P(H->M) the probability in H to get M.
In Helsinki, he tries to evaluate his chance to get Sidney.
With one reasoning, he (the H-guy) thinks that P(H-M) = 1/2, and
that P(M-S) = 1/2, and so conclude (multiplication of independent
probability) that P(H-S) = 1/2 * 1/2 = 1/4.
But with another reasoning, he thinks that the duplications give
globally a triplication, leading eventually to a copy in W, a
copy in S and a copy in B, and so, directly conclude P(H-S) = 1/3.
So, is it 1/4 or 1/3 ?
Neither. The probability that the guy starting from Helsinki gets
to Sydney is unity.
Try to convince the guy who gets to Beijing, or the one who stayed
in Washington. He knows that the probability evaluated in Helsinki
was not P(Sidney) = 1.
We start with John Clark in Helsinki, so P(JC ~ H) = 1. By
construction, after the duplication and so on, P(JC ~ W) = P(JC ~ S)
= P(JC ~ B) = 1. (I use '~' as a shorthand for 'in' or 'sees'.)
In the 3-1 view, that is correct. But in my posts I insist that "W",
"M" denotes the experience of opening the door or the reconstitution
box, and writting in the personal diary which cities is seen. In that
case, obviously, P(W), P(S) and P(B) cannot be all equal to one as W,
S and B are incompatible event.
JC in Helsinki knows the protocol, so he can easily see that these
are the correct probabilities. So, as I said, the probability that
the guy starting from Helsinki gets to Sydney is unity. Any other
interpretation of this scenario involves an implicit appeal to
dualism -- there is "one true JC" that goes through these
duplications, and he can only ever end up in just one place.
Not at all. By comp we agree that they are all the true JC, and that
they all see, taken together, all cities. But the question is about
the personal events lived by the H-guy after he will push the button,
and that makes the events (1p-events) incompatible.
As John Clark has correctly pointed out, your intuition and
formalism simply does not work in the presence of person-duplicating
machines.
It works very well, but you need to distinguish between the outsider
view: all JC see all cities, and each personal views obtained, which
are incompatible.
You simply borrox John Clark confusion between the 3-1 views and the 1-
views.
There is no single 1p view -- there are three possible 1p views in
the triplication scenario.
Right. The point is that from the first person perspective, those 1-
views are logically incompatible.
So, again, John Clark is right when he says that JC ~ H will see
three cities (W, S, and B) after the experiment is completed.
yes, he is right, but only on the 3-1 view on those 1-views, not on
the 1-views seen by the 1-views, which are incopatible, and which was
what the prediction asked was all about.
If, as you claim, he will see only one city, you have to have some
dualist 'nut or core' that survives in only one of your copies.
Of course not. Just do the tought experience, and consider all 1-
views, as seen from each of them.
Do you agree that if you are promised a cup of coffee in both W and in
M, you can bet in Helsinki that you will get a cup of coffee with
certainty? if yes, it is the same for the question "how many city will
the H-guy seen, from its personal pov, after pushing the button?". The
answer is "only one city", or "I will drink a cup of cofffe in ONE
city with P = one, but I cannot know which one".
Of course, as I said some time ago, the easiest resolution of you
logical conundrums is that JC ~ H does not survive, and that
there are three new persons, one in each city, so the probability
that JC in H will see Sydney is exactly zero.
Then you predict that you will not survive either with a simple (non-
duplicating) teleportation, or with a brain transplant, and we die ar
each instant. That is OK (G and G* concures, but again, it is in a 3p
picture, contradicted by the 1-views, boith intuitively, and
mathematically.
Looking at the more realistic quantum realization of this
triplication scenario, we can formulate that as follows. We prepare
a spin-half atom with spin along the x-axis, then pass it through an
S-G magnet oriented along the y-axis, getting two possibilities,
which we can call up and down. We then take the up channel and pass
that through a further S-G in the x-direction, getting two further
possibilities of left or right.
Let us perform this experiment many times and count the number of
particles in each of the three possible final states (down, left,
and right). If this is a real laboratory experiment, in which
detection of a particle in any channel leads to irreversible
decoherence and the formation of a separate world containing just
that result, we will find approximately half the particles end up in
the down state, and approximately a quarter in each of the left and
right states. This gives the most reliable estimate of the real
probabilities for the outcome from the given initial state.
If you take the MWI view, then you get one down, one left, and one
right in every run of the experiment, so the probability for each
outcome is unity. In order to get probability of 1/4 for left, say,
you have to detect the absence of a particle in the down state (so
that the particle is certainly in the up state) for which the
probability is 1/2.
Actually, your preferred answer -- that the probability P(H->S) = 1/3,
?
I explained that P = 1/4 is more plausible, unless the guy remains
asleep at the Moscow transit.
is possible only in a fully dualist model. You are essentially
claiming that as the scenario puts John Clark's in all three cities,
it is purely a random chance that selects one of them to be the
"true" John Clark -- a dualist "core" is assigned to one of these
copies purely by chance.
On the contrary, I have always insisted that all three of them are
equally real and conscious, and equal in the right to claim they were
the H-guy.
But just put yourself in their places: they all feel like if a
selection has occurred. The same when you measure a spin in QM, the
indterminacy comes from the realisation of all the alternatives,
without invoking dualism, like in Copenhagen.
This is the problem with probabilities in the MWI -- how do you
interpret probabilities when all possible outcomes occur with
probability one?
The probabilities concern the relative first person experiences.
Computationalism guaranties that there will be only one outcome.
You are simply talking nonsense, here. "Relative first person
experiences"? Relative to what?
In our protocol, relative of being the helsinki guy.
The scenario, and computationalism guarantees that there will be all
three outcomes.
In the 3-1 view, that is correct, but like John Clark, you dismiss
that the question is about the experience which will be left, as seen
by the experiencer himself (herself). Those are incompatible
alternatives. Nobody will live those experiences at once. each of them
will feel like being in once city, with honorable doppelgangers in the
other city or cities.
If there is only one "1p" experience, then that can only be chosen
dualistically.
Not at all. the beauty of computtaionalism, is that it explains why we
feel like there is a dualism, but we know that it is an illusion due
to the duplication of the diaries, which cannot contains statements
like "I open the door and saw W and M blurred into one experience".
for that, you need to add telepathy and spooky action at a distance.
If there is duplication (triplication) then your intuitions break
down. I have to say it -- John Clark has been right all along.
John Clark has confused the 1-views and the 3-1-views all along, and
you just borrow its confusion, I'm afraid.
That confusion is of course the confusion that if we pursue lead to
the elimination of the 1-view, like with the eliminativist materialist
(Churchland, Dennett, ...), which is just the aristotelian technic to
put the mind-body problem under the rug, since a long time (but not
done by Aristotle Himself, only by the non rigorous successors.
Bruno
Bruce
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