On 9/9/2015 10:27 AM, Bruno Marchal wrote:
On 09 Sep 2015, at 07:55, Quentin Anciaux wrote:
2015-09-09 7:39 GMT+02:00 Brent Meeker <[email protected]
<mailto:[email protected]>>:
On 9/8/2015 8:20 PM, Stathis Papaioannou wrote:
On 9 September 2015 at 12:44, Bruce Kellett
<[email protected] <mailto:[email protected]>>
wrote:
On 9/09/2015 12:26 pm, Stathis Papaioannou wrote:
On 9 September 2015 at 10:43, Bruce Kellett
<[email protected]
<mailto:[email protected]>> wrote:
On 9/09/2015 9:30 am, Stathis Papaioannou wrote:
On 9 September 2015 at 09:23, Bruce Kellett
<[email protected]
<mailto:[email protected]>> wrote:
On 9/09/2015 8:56 am, Stathis Papaioannou wrote:
On 8 September 2015 at 22:11, Bruce Kellett
<[email protected]
<mailto:[email protected]>> wrote:
On 8/09/2015 9:14 pm, Stathis Papaioannou wrote:
On 8 September 2015 at 20:48, Bruce Kellett
<[email protected]
<mailto:[email protected]>> wrote:
On 8/09/2015 8:40 pm, Stathis
Papaioannou wrote:
On 8 September 2015 at 17:39, Bruce
Kellett <[email protected]
<mailto:[email protected]>> wrote:
On 8/09/2015 4:56 pm, Stathis
Papaioannou wrote:
I will ask you the same question
as I did Brent: do you conclude
from the fact that when you toss a
coin it comes up either as head or
tails that the world does not
split into two parallel versions
of you, one of which sees heads
and the other tails?
I would conclude that a coin toss
does not provide any evidence for
multiple worlds or a split. The
only evidence we have from this
data is that the outcome of the
toss is uncertain. There is no
evidence there for any split of
anything.
It is not evidence FOR a split but is
it evidence AGAINST a split?
It is evidence that the assumption of a
split is not necessary in order to
understand everyday happenings. So, by
the application of Occam's Razor, no
split happens.
So you agree that we would still observe the
probabilities we do if we lived in a
deterministic world in whaich all
possibilities are realised?
No, because not all possibilities happen in
this world. If all possibilities were
realized in this world, then there would be
no uncertainty, no probabilities. Possibility
and actuality would be the same thing. All
the horses would win the Melbourne cup; and
we don't live in such a world.
Obviously, not all possibilities happen in this
world, but they might happen in parallel worlds
that don't interact with each other. The argument
is that probabilities emerge from this, since you
don't know which world you will find yourself in.
You bet on the favourite in the race because you
think you are more likely to end up in a world in
which the favourite wins.
In other words, probabilities can make perfect
sense in a single deterministic world. This was
understood a long time ago with the development of
statistical mechanics. The idea that "all
possibilities happen in parallel worlds" does not
actually make a lot of sense. There is no current
physical theory that implies this (without the
addition of a lot of unevidenced assumptions). So
probabilities do not emerge from this, they come
from quite simple assumptions of randomness and
ignorance.
Probability in the MWI of quantum mechanics is
problematic. Regardless of claims to be able to
derive the Born Rule in Everettian models, all
attempts fail because they are circular -- they
need the Born rule in order to have
non-interacting worlds, so you cannot then use
these independent worlds to derive the Born rule.
Gleason's theorem is no help -- it suffers from
all the same problems as the Deutsch-Wallace approach.
You don't seem to be disputing that we would still
experience a probabilistic world even if all
possibilities were actually realised, even though you
do dispute that we in fact live in such a world.
I'm not sure if you are disputing that, to give a
simple model case, if a coin was tossed and the world
split in two, with one version of you seeing heads and
the other tails, the probability of each outcome is 1/2.
Whether or not all possibilities are realized, they are
not in evidence, so their relevance to the question of
probabilities is questionable.
Your simple model case of a coin toss causing a world
split is just a made-up example to give the result you
want, so again its relevance is dubious. There is no
sensible physical theory in which the world splits on
classical coin tosses.
If you can't imagine a world split, consider a virtual
reality in which the program forks every time a coin is
tossed, one fork seeing heads and the other tails. You are
an observer in this world and you have this information, so
you know for certain that "all possibilities are realised"
when the coin is tossed. What would you say about your
expectation of seeing heads?
I presume you mean that the world is duplicated on each
toss, with one branch showing each outcome. We are back to
the dreaded "person duplication" problem. My opinion on this
is that on such a duplication, two new persons are created,
so the probability that the original person will see either
heads or tails is precisely zero, because that person no
longer exists after the duplication.
After the coin has been tossed a few times, you (or one of the
entities identifying as you) will say that, despite the opinion
he expressed on 9th September on the Everything List, it does
seem that he has survived the duplication and that heads comes
up about half the time.
But he would say the same thing if only one fork of the program
were executed at each branch. So whether the other branches are
executed is not related to observations.
Hence probability is not linked with true randomness but from
appereance of randomness from a 1st person POV.
As for Bruce, could you then be honest, and simply say you don't
believe in the many world interpretation and don't want to explore
it... yes we're talking mostly metaphysics on this list, if you
dislike it, I wonder what you're doing here.
Indeed the point is notably that we can reason about this, that is
doing science, so that we never disagree except about the choice of
the assumptions.
Now, I disagree with Bruce, and I guess many philosophers and
scientists, except Deutsch (on this), but I do think that QM (without
collapse) is a theory of many worlds (in a perhaps admittedly more
abstract than usual notion of world).
If we define a physical world by a set of events close for interaction,
But can computationalism give a coherent account of this? Doesn't the
UD imply at every set of events will have many (countably many?) causal
histories and infinitely many causal futures.
then the "many-world" is a consequence of the linearity of the wave
evolution together with the linearity of the tensor product.
But they are only "many" FAPP. Decoherence suppresses cross terms in
the density matrix, but it doesn't make them zero - and I don't think
it's even provable that there is a unique basis in which it diagonalized
FAPP. And of course we have no theory of quantum spacetime. QM assumes
a continuous spacetime, so QM is not the last word and if
computationalism only reproduces QM it will fail when QM fails.
Brent
People wanting one definite physical reality need to speculate about a
selection principle.
Then computations are athmetical notions, and bu virtue of (provable)
true relations among numbers, all computation are realized in a tiney
part of the arithmetical reality, in which case we get the many dreams
or histories, once we look at the realizable computational relative
"mental states".
Bruce seems coherent to me, just that he assume that personal identify
is determined and make unique by a continuous analog (non digital)
physics.
Wit computationalism we expect a continuum physics, but only because
we are muliplied continuously on different and divergent computational
histories + "real oracles".
Bruce assumes a physical universe, and betrays his Aristotelian
assumption when saying that something is a speculation if not seconded
by physical evidences.
A platonist can trust physical evidences for abandoning a theory, but
he will remain skeptical on any identification between reality and the
physical evidences or the last non refuted theory unifying those
evidences, which, for him, should be explained from simpler
principles, and not avoid the main question (why consciousness, why
does that hurt?) which are lost in any 3p extensional theory (like
physics, or classical analysis).
Bruce theory is coherent, but the price is that even simulating him at
the string/brane level, or whatever theory unifying gravity with the
quantum, and this with 100^100 real decimals exact (fr the complex
amplitudes) will not make it possible for a conscious being to
manifest itself. As it it doubtful that such simulated entity will
behave differently than a human being (or the string/brane theory is
refuted!), it means that such theory make zombies possible.
We are just wittnessing the Aristotelian resistance, but Bruce is
logically correct to resist computationalism, and the "literal
interpretation of the double linearity of QM", which is more than
welcome for a computationalist as it guaranties the sharing of the
computations: it saves us from solipsism, and that is why it is
encouraging that the physical modalities seems to go toward the
quantum mathematics too.
What a thread! The question debated can be sum up by am I a real
number or a natural number?
Bruno
Quentin
Brent
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