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

[scerir]

Rafal Smigrodzki
> Seriously, MWI does seem to scare many people because 
> of its implications - infinities of creatures, hell-branches, 
> total godlessness. For some reason the framers of QM felt 
> they needed to invent "collapse" out of whole cloth, 
> and only Everett, thirty years later, had the gumption 
> to work out the details, take QM to its simplest form 
> and do away with anthropocentrism. 

It seems, perhaps, interesting to point out that the first 
definition of 'collapse' was 'reduction of probability packet', 
sometimes 'reduction of wave packet.'

H. Kragh ('Dirac: a Scientific Biography', Cambridge UP,1990)
describes Dirac, Heisenberg and Born having a discussion,
in 1927, about what may cause a 'collapse'. Dirac said 
that it is 'Nature' that makes the choice (of the measurement 
outcome). Born agreed. Heisenberg however maintained that,
behind the collapse, and the choice of which 'branch' 
the wavefunction would take, there was 'the free-will of 
the human observer'.

Actually Heisenberg described the 'collapse' in 1930, speaking 
of the M-Z interferometer. "There is then a definite 
probability for finding the photon either in one part 
or in the other part of the divided wave packet. After 
a sufficient time the two parts will be separated by any
distance desired; now if an experiment yields the result that
the photon is, say, in the reflected part of the packet, then
the probability of finding the photon in the other part of the
packet immediately becomes zero. The experiment at the position
of the reflected packet thus exerts a kind of action (reduction
of the wave packet) at the distant point occupied by the transmitted
packet, and one sees that this action is propagated with a velocity
greater than that of light. However, it is also obvious that
this kind of action can never be utilized for the transmission
of signals so that it is not in conflict with the postulates
of the theory of relativity." ('The Physical Principles of the
Quantum Theory', University of Chicago Press, Chicago, 1930).

But later, in 'Physics and Philosophy' (Harper and Row, 1958, N.Y.)
Heisenberg writes: "The observation itself changes the probability
function discontinuously; it selects of all possible events
the actual one that has taken place [...]. The discontinuous change
in the probability function, however, takes place with the act
of registration, because it is the discontinuous change
of our knowledge in the instant of registration that has its
image in the discontinuous change of the probability function."

"This probability function represents a mixture of two things,
partly a fact and partly our knowledge of a fact. It represents a
fact in so far as it assigns at the initial time the probability
unity (i.e., complete certainty) to the initial situation: the
electron moving with the observed velocity at the observed position;
'observed' means observed within the accuracy of the experiment.
It represents our knowledge in so far as another observer could
perhaps know the position of the electron more accurately. The error
in the experiment does - at least to some extent - not represent a
property of the electron but a deficiency in our knowledge of the
electron. Also this deficiency of knowledge is expressed in the
probability function." [Heisenberg, Physics and Philosophy].

J. von Neumann helps here (maybe) to understand what Heisenberg
might have in mind: "It is inherenly entirely correct that 
the measurement or the related process of the subjective 
perception is a new entity relative to the physical environment 
and is not reducible to the latter. Indeed, subjective perception 
leads us into the intellectual inner life of the individual, 
which is extra-observational by its very nature". J. von Neumann, 
Mathematical Foundations of Quantum Mechanics, p.418.

J. von Neumann also defines the principle of 'psycho-physical
parallelism'. He defines it as the principle "that it must 
be possible to describe the extra-physical process of 
the subjective perception as if it were in reality 
in the physical world - i.e., to assign to its parts 
equivalent physical processes in the objective environment, 
in ordinary space."

Heisenberg by the way goes on to say: "We can, for instance, 
predict the probability for finding the electron at a later 
time at a given point in the cloud chamber. It should be 
emphasised, however, that the probability function does not 
in itself represent a course of events in the course of time.
It represents a tendency for events and our knowledge of events."
And a little further, he says: "The observation ... breaks 
the determined continuity of the probability function by changing 
our knowledge of the system."

And also: "Therefore, the transition from the 'possible' 
to the 'actual' takes place during the act of observation. 
If we want to describe what happens in an atomic event, 
we have to realize that the word 'happens' can apply only 
to the observation, not to the state of affairs between two 
observations. It applies to the physical, not the psychical act 
of observation, and we may say that the transition from the 
'possible' to the 'actual' takes place as soon as the
interaction of the object with the measuring device, and 
thereby with the rest of the world, has come into play; it is not 
connected with the act of registration of the result by the mind 
of the observer. The discontinuous change in the probability 
function, however, takes place with the act of registration, 
because it is the discontinuous change of our knowledge in 
the instant of registration that has its image in the discontinuous 
change of the probability function."

According to Jan Faye "Bohr accepted the Born statistical
interpretation because he believed that the psi-function
has only a symbolic meaning and does not represent anything real.
It makes sense to talk about a collapse of the wave function
only if, as Bohr put it, the psi-function can be given a pictorial
representation, something he strongly denied." 

It seems to me that the 'Copenhagen interpretation' (an 
invention of Heinsenberg, dated 1954, if I remember well) 
and - in any case - the so called 'Spirit of Copenhagen' and 
the 'orthodox' interpretation, gave no sharp definition of 
'collapse' (and of 'wave-function') in terms of 'ontic' 
reality. They introduced the concept of 'psycho-physical 
parallelism'. But this very concept is crucial in the 
Everett's 'relative state' interpretation.