[extropy-chat] Popper and QT

[scerir]

From: "gts" 

> I can't defend Popper's book on the subject 
> (_Quantum Theory and the Schism in Physics: 
> From the Postscript to the Logic of Scientific  
> Discovery_) because I have yet not read it. 
> However I wonder if his views on this subject 
> were not given the credit they might have 
> deserved simply because he was a philosopher 
> of science rather than a physicist.

Sir Karl Raimund Popper was not strong in 
math. People still remember a conference he
gave in Trieste, about quantum paradoxes,
and his blackboard was full of technical
nonsenses. 

Nevertheless he invented an interesting gedanken  
('Zur Kritik der Ungenauigkeitsrelationen', 
in 'Die Naturwissenschaften', 22, 807-808, 1934) 
experiment, involving two particles ('entangled', but
this term was invented one year later).

Einstein did not believe that Popper's gedanken
experiment could have been carried out. The problem
was this: to predict position and momentum of particle 1,
both time and energy of the entangled particle 2 have 
to be measured simultaneously, which appeared to be
impossible to Einstein, following Heisenberg. 

According to Nathan Rosen (the 'R' in 'E.P.R.') it might
have been possible that Popper's experiment (1934)
influenced Einstein, and the paper by E.P.R. (1935).
Actually the reasoning by E.P.R., in their paper,
is similar to Popper's reasoning, criticized by 
Einstein the previous year. (Bohr's response to E.P.R.
is similar to Einstein's response to Popper!).

Kim and Shih performed an experiment similar to Popper's,
with unexpected results.
http://www.arxiv.org/abs/quant-ph/9905039

(The experiment has nothing to do with 'propensities'
or with Heisenberg-Aristotle 'potentia', which
have more to do with the 'amplitudes' - between two
measurements - than with the probabilistic outcome 
of a measurement. There is - perhaps - a sort of revival 
of these concepts in the so called two-state time-symmetrical 
quantum formalism by Aharonov, Lebowitz, Bergmann, 
or in the 'non-demolitive' quantum measurements). 
  
> No matter who was right, we're still left 
> with this curious complementarity principle 
> of Bohr's which really makes no sense  
> whatsoever.

That curious principle (but not so curious or vague
as we believe [1[) is the heart of a new general principle,
named the 'indistinguishability' principle
(sometimes the 'finite information' principle). 

[1]
'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'. 
[Bohr, Atomic Theory and the Description of Nature, pp.97-8, 
Cambridge University Press, 1934]