[ExI] Psi in a major science journal, J. Personality and Social Psychology

scerir scerir at alice.it
Thu Oct 21 09:37:28 UTC 2010

> Either explanation boggles the hell outta my mind, and I can't help getting
> the feeling there must be (there MUST BE!) some alternate explanation that
> no one has thought of yet.  Please anyone here, I am open to suggestion,
> waaaay open: how and why does the double slit experiment work?
> spike

According to Bohr the problem is due to the very existence of the "quantum of action"

'However, since the discovery of the quantum of action, we know that the classical ideal
cannot be attained in the description of atomic phenomena. In particular, any attempt at
an ordering in space-time leads to a break in the causal chain, since such an attempt is
bound up with an essential exchange of momentum and energy between the individuals and the
measuring rods and clocks used for observation; and just this exchange cannot be taken
into account if the measuring instruments are to fulfil their purpose. Conversely, any
conclusion, based in an unambiguous manner upon the strict conservation of energy
and momentum, with regard to the dynamical behaviour of the individual units obviously
necessitates a complete renunciation of following their course in space and time'.
-Niels Bohr, Atomic 'Theory and the Description of Nature', pp. 97-8,
Cambridge University Press, 1934.

Here is a gedanken experiment (due to Zurek and Wootters, 1979).
Imagine a two-slit interferometer and photons arriving at the screen.
When we say "photons" we do not mean "particles", and we do not mean
"waves", in general we mean "particle-waves", since a "wave" is something
existing on the future (still to be measured), while "particle" is someting existing
in the past (already measured). So, you get the usual interferential pattern
(because there are, for each photon, two "amplitudes" coming from each of the
two slits). Now, let us suppose, for a moment, we have a "smart" screen
which can register, for each photon arriving at the screen, from the two slits, both
its position (the point of impact at the screen) and its momentum (that is to say,
the direction from the single slit it entered to the point of inpact at the screen -
- here we assume that geometric optics holds, and this is a strong assumption.)
What would now be the pattern on the "smart" screen? An interferential pattern,
because the screen registers the positions? Or a smooth pattern, because the
"smart" screen also registers the momentum (thus distinguishing the paths)?
Momentum and position are, of course, observables which do not commute.

Well, according to Bohr, the situation, with regard to the dynamical behaviour of the
individual photons arriving at the screen, necessitates a *renunciation* of following
their course in space and time.

In other words or the assumption of geometric optics is wrong, or our "smart" screen,
because it can register the momentum (and the direction) of each photon arriving
at the screen, would cause a retro-action on each travelling photon, transforming
the potential interference pattern into an actual smooth pattern.

Another way to put it is in terms of finiteness information (Zeilinger). That is to
say that a single quantum only carries a limited quantity of available information
about itself. So you can ask something (i.e. from which slit do you come?) and
you get the exact answer, at the cost of loosing any other information, since
the apriori available information is limited and finite.

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