[ExI] Many Worlds (was: A Simulation Argument)

[scerir]

Damien 
> "...there is a quantity called a probability amplitude associated 
> with every method whereby an event in nature can take place... we can 
> associate an amplitude with the overall event by adding together the 
> amplitudes of each alternative method... Next, we interpret the 
> absolute square of the overall amplitude as the probability that the 
> event will happen." (p. 19)
> 
> So yes, Serafino, "that [is] a mixture of MWI and path integral 
> formalism"... to my untutored eye.

In MWI the traditional superposition of states
|a> + |b> + ...
becomes, upon measurements, a superposition of relative states
|a>|outcome a>|observer a> + |b>|outcome b>|observer b> + ...
via the tensor product and the *Hilbert space* formalism.
The signature of quantish nature, the interference,
is sometimes explained in terms of interference
between 'worlds' ....

In the path integral approach every quantum system is
described as a *particle* and the probability
that a particle goes from (x1,t1) to (x2,t2) - where
x are *positions in space* and t are *times* - 
is given by P(2,1) = |K(2,1)|^2
where K is the probability amplitude propagator,
calculated from the sum over all possible paths,
from (x1,t1) to (x2,t2), given the classical
action S(t2,t1) for each path. Notice that
the interval (t2,t1) is fixed.
Notice that, in an orthodox interpretation,
individual trajectories form an average to
obtain the final quantum outcome, but these
trajectories are not all 'physical'.

As you can perhaps see there is some difference 
between the two approaches (at least to my
also untutored eye).     
 
> The dreaded Sarfatti comments, without providing a reference to Albert:
> <David Albert has shown that one can beat the Heisenberg uncertainty 
> principle for special pairs of incompatible observables in a 
> "self-measurement" which also involves "photographs of other worlds" 
> violating the dogma of Everett's original meta-theory of "many 
> worlds" for the meaning of quantum mechanics. Everett mistakenly 
> assumed that conscious observers could never be aware of their 
> parallel selves in the "universes next door". 

That paper should be this one
http://kh.bu.edu/qcl/pdf/albert_d1983066c6d7c.pdf
there is another, more philosophical, paper by David Z 
Albert, about quantum-mechanical automata, which
is simpler but less effective.
But that 'self-measurement' is usually called 
a 'pre-measurement', different from a non-reversible 
'measurement' (aka reduction, collapse, projection, 
split, decoherence, selection, or - as Bohr named it - 
'amplification'). So you can imagine why a 
quantum-mechanical automaton, performing self-measurements,
can 'feel' different 'worlds', but cannot explain
to others what he feels. No, no, ... that 'qualia'
thing again!