# Re: Many Pasts? Not according to QM...

Hi Saibal,

Le 27-mai-05, à 14:29, Saibal Mitra a écrit :

----- Oorspronkelijk bericht -----
Van: "Stathis Papaioannou" <[EMAIL PROTECTED]>
Aan: <[EMAIL PROTECTED]>
CC: <[EMAIL PROTECTED]>; <everything-list@eskimo.com>
Verzonden: Friday, May 27, 2005 01:44 AM
Onderwerp: Re: Many Pasts? Not according to QM...

Saibal Mitra wrote:

Quoting Stathis Papaioannou <[EMAIL PROTECTED]>:

On 25th May 2005 Saibal Mitra wrote:

One of the arguments in favor of the observer moment picture is that
it
all
possible observer moments on which a measure is defined (which can be calculated in principle using the laws of physics), then the paradox
never
arises. At any moment you can think of yourself as being randomly
drawn
from
the set of all possible observer moments. The observer moment who has survived the suicide experiment time after time after time has a very
very
very low measure.

I'm not sure what you mean by "the paradox never arises" here. You
have
said
in the past that although you initially believed in QTI, you later
realised

that it could not possibly be true (sorry if I am misquoting you, this
is
from memory). Or are you distinguishing between QTI and QS?

That's correct. In both QTI and QS one assumes conditional probabilities.
You just
throw away the branches in which you don't survive and then you conclude
that you
continue to survive into the infinitely far future (or after performing
an
arbitrary
large number of suicide experiments) with probability 1.

But if you use the a priori probability distribution then you see that
you
the measure
of versions of you that survive into the far future is almost zero.

What does "the measure of versions of you that survive into the far future is almost zero" actually mean? The measure of this particular version of
me
typing this email is practically zero, considering all the other versions
of
me and all the other objects in the multiverse. Another way of looking at
it
is that I am dead in a lot more places and times than I am alive. And yet
undeniably, here I am! Reality trumps probability every time.

You have to consider the huge number of alternative states you could be in.

1) Consider an observer moment that has experienced a lot of things. These experiences are encoded by n bits. Suppose that these experiences were more or less random. Then we can conclude that there are 2^n OMs that all have a
probability proportional to 2^(-n). The probability that you are one of
these OMs isn't small at all!

2) Considering perforing n suicide experiments, each with 50%  survival
probability. The n bits have registered the fact that you have survived the n suicide experiments. The probability of experiencing that is 2^(-n). The
2^(n) -1 alternate states are all unconscious.

So, even though each of the states in 1 is as likely as the single state in
2, the probability that you'll find yourself alive in 1 is vastly more
likely than in 2. This is actually similar to why you never see a mixture of two gases spontaneously unmix. Even though all states are equally likely,
there are far fewer unmixed states than mixed ones.

Saibal

I agree in the case I could imagine all the "observer moments" in some complete third person way, where the notion of "dying" can be given some third person sense. But the compi and the qti, relies, it seems to me, on the fact that we cannot experience not being there. So that in both case the first person probabilities are one, from first person points of view. They are one, *almost* by definition, the very notion of "probabilitiy" presupposes the ability to test the outcome of a (random) *experiment* (this is still more plausible for an "observer-moment" first person *experience*).

Do you see what I try to say?

That's why we need some "no cul-de-sac" hypothesis.

[For those who knows the (Godel Lob Solovay) provability logics (G and G*) : you can go from a provability logic Bp (= G; with cul-de-sac accessible from all transitory obsever momente) to a probability logic (without cul-de-sac) by *imposing* consistency: Bp ==> Bp & -B-p. (-B-p = 'Consistent p' remember the dual of Bp is -B-p, and with Bp read as 'Provable p', ('Beweisbar p', in German), -B-p is 'Consistent p'. And if you remind Kripke Semantics, Con p, means there is at least one observer moment (with p true) accessible from you current observer moment. Of course G* proves Bp <-> (Bp & -B-p), But G* proves also -B(Bp <-> (Bp & -B-p)), so that from the machine point point of view, it will change the provability logic, indeed, it changes it into a probability logic.]

In my 1988 paper, I argue that the qti is a confirmation of the compi. (Given that the uda shows comp entails the no cul-de-sac hypothesis).

Or you are (still) with the ASSA ? Or do I miss what you try to explain?

Bruno

http://iridia.ulb.ac.be/~marchal/