Le 16-avr.-08, à 03:24, Russell Standish a écrit :

>
> On Wed, Apr 16, 2008 at 02:22:23AM +0200, Saibal Mitra wrote:
>>
>>> First off, how is it that the MWI does not imply
>>> quantum immortality?
>>
>> MWI is just quantum mechanics without the wavefunction collapse 
>> postulate.
>> This then implies that after a measurement your wavefuntion will be 
>> in a
>> superposition of the states corresponding to definite outcomes. But we
>> cannot just consider suicide experiments and then say that just 
>> because
>> branches of the wavefuntion exist in which I survive, I'll find 
>> myself there
>> with 100% probability. The fact that probabilities are conserved 
>> follows
>> from unitary time evolution. If a state evolves into a linear 
>> combination of
>> states in which I'm dead and alive then the probabilities of all these
>> states add up to 1. The probability of finding myself to be alive at 
>> all
>> after the experiment is then less than the probability of me finding 
>> myself
>> about to perform the suicide experiment.
>>
>> The probability of me finding myself to be alive after n suicide 
>> experiments
>> decays exponentially with n. Therefore I should not expect to find 
>> myself
>> having survived many suicide experiments. Note that contrary to what 
>> you
>> often read in the popular accounts of the multiverse, the multiverse 
>> does
>> not split when we make observations. The most natural state for the 
>> entire
>> multiverse is just an eigenstate of the Hamiltonian. The energy can 
>> be taken
>> to be zero, therefore the wavefunction of the multiverse satisfies the
>> equation:
>>
>
> One should also note that this is the ASSA position. The ASSA was
> introduced by Jacques Mallah in his argument against quantum
> immortality, and a number of participants in this list adhere to the
> ASSA position. Its counterpart if the RSSA, which does imply quantum
> immortality (provided that the no cul-de-sac conjecture holds), and
> other list participants adhere to the RSSA. To date, no argument has
> convincingly demonstrated which of the ASSA or RSSA should be
> preferred, so it has become somewhat a matter of taste. There is some
> discussion of this in my book "Theory of Nothing".


Actually, I am not sure the ASSA makes sense once we take into account 
the distinction between first and third person point of view. Comp 
immortality is an almost trivial consequence that personal death cannot 
be a first person experience at all. Quantum immortality is most 
plausibly equivalent with comp immortality if the "quantum level" 
describes our correct comp substitution level. But this does not mean 
that we can know what shape the comp immortality can have, given that 
comp forbids us to know which machine we are or which computations bear 
us. We have not yet answered the question of how many first persons 
are. If it is one, amoeba duplication already entails immortality, 
although not necessarily a reassuring (or frightening) one like some of 
those suggested by some religion or popular beliefs. We are mainly 
ignorant of those matters, and necessarily so, in case comp (or its 
transfinitely many weakenings) is (are) correct.
But we can make inferences, i.e. theories, and *define* matter by the 
explicit addition of the no-cul-de-sac principle, by adding Dt to Bp, 
going from the primary hypostases to the secondary one: this gives a 
quantum propositional theory of matter but this (lobian) theory is 
still in lack of a good tensor product capable of extracting a non 
trivial first person *plural* notion. Strictly speaking, it remains 
amazing we can interact ...

Bruno


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


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