[extropy-chat] Popper and QT

[scerir]

From: "gts"
But not having read this one of Popper's books devoted 
to QT, or having studied this experiment in detail 
(from my brief scan of the paper above it appears Popper 
was right but perhaps for the wrong reasons), I'll defer
to you and take your word for it that this experiment 
was not conclusive proof of and may have no bearing on 
Popper's objective philosophy of probability.


Although Popper perceived that his subtle gedanken experiment was
a wrong and in any case an 'overdetermined argument' (Max Jammer),
he published it many times, with refiniments.

K. R. Popper, Die Naturwissenschaften 22, 807 (1934).
K. R. Popper, Quantum Theory and the Schism in
              Physics, Hutchinson, London (1982).
K. R. Popper, in Open Questions in Quantum Physics,
              Tarozzi G, van der Merwe A (eds.),               
              Dordrecht (1984).
K. R. Popper, Nature 328, 675 (1987).
K. R. Popper, Nature 329, 112 (1987).

Essentially he was both trying to falsify a prediction of 
(the formalism of) quantum mechanics, Heisenberg's interpretation 
of quantum 'collapse' in terms of (subjective, according 
to Popper) knowledge.

He was also trying to test his own realistic interpretation 
of quantum effects, based on actual and local 'propensities'.

The set up was simple. Essentially (but there are many other
configurations and possible tunings): a source 's' of two 
(position/momentum) entangled photons 'p1' and 'p2', a narrow 
slit on the left, and many detectors 'D' on the right.

                                             D2
|                                            D1
 <-----p1-----------s---------p2------->     D0
|                                            D3
                                             D4

QM predicts that the slit (on the left side) 'measures' 
the position of photon p1, hence it measures the position 
of the entangled (position correlation) photon p2,
hence the momentum of photon p2 is 'spread' (due to 
position/momentum Heisenberg uncertainty relation) 
and p2 hits one of those detectors on the right, 
and not necessarily the detector D0 on the straight line.
(It is possible to show it easily, details are
given, I guess, in the literature cited below).

In Popper's words 'To sum up: if the Copenhagen
[rather Heisenberg's] interpretation is correct,
than any increase in the precision of out mere
knowledge of the position of the particles going to
the right should increase their scatter; and this
prediction should be testable.'

Needless to say Popper's own model states that 
the behaviour of photon p2 does not depend at all 
on the slit on the left (measuring position of photon p1).

Experiments done, since 1995, (below) confirm the prediction
of QM. Popper's argument (no less subtle than E.P.R.'s 
realistic argument) is then wrong.

But this does not mean that the mere _subjective_ knowledge
of the position of photon p1, measured by the slit on the
left, _causes_ the sudden 'ghost' scattering of photon p2
on the right. So, in a certain sense, Popper was also 
a bit right.

s. 

- Two-Photon Entanglement and Quantum Reality (1997)
in this page http://physics.umbc.edu/Faculty/shih.html

- Experimental Observation of Two-Photon "Ghost" 
Interference and Diffraction", Physical Review Letters, 
v.74, p.3600 (1995)
in this page (see year 1995) 
http://people.bu.edu/alexserg/references.html

- Optical Imaging by Means of Two-Photon Quantum 
Entanglement, Physical Review A , v.52, pp. R3429-3432 (1995)
in this page (see year 1995) 
http://people.bu.edu/alexserg/references.html