Re: Fotone, cristalli e polarizzazione

From: Giorgio Pastore <pastgio_at_units.it>
Date: Fri, 19 May 2017 09:05:27 +0200

Il 18/05/17 20:38, Marco Giampaolo ha scritto:
....
> Per quanto riguarda le frasi in questione penso che Dirac stia solo
> affermando che la fisica teorica debba fornire modelli atti a predire
> i risultati di esperimenti senza pensare alle "cause prime" dietro
> questi comportamenti. ....

Dira scrive:
"A question about what will happen to a particular Photon under
certain conditions is not really very precise. To make it precise one
must imagine some experiment performed having a bearing on the
question and inquire what. will be the result of the experiment- Only
questions about the results of experiments have a real significance
and it is only such questions that theoretical physics has to consider.
In our present example the obvious experiment is to use an incident
beam consisting of only a Single Photon and to observe what appears
on the back side of the crystal. According to quantum mechanics
the result of this experiment will be that sometimes one will find a
whole Photon, of energy equal to the energy of the incident Photon,
on the back side and other times one will find nothing. When one
hands a whole Photon, it will be polarized perpendicular to the optic
axis. One will never find only a part of a Photon on the back side.
If one repeats the experiment a large number of times, one will find
the Photon on the back side in a fraction sin(c) of the total number
of times. Thus we may say that the Photon has a probability sin(c).
of passing through the tourmahne and appearing on the back side
polarized perpendicular to the axis and a probability cos2, of being
absorbed. These values for the probabilities lead to the correct
classical results for an incident beam containing a large number of
photons.
In this way we preserve the individuality of the Photon in all
cases. We are able to do this, however, only because we abandon the
determinacy of the classical theory. The result of an experiment is
not determined, as it would be according to classical ideas, by the
conditions under the control of the experimenter. The most that tan
be predicted is a set of possible results, with a probability of occurrence
for each."


Sta quindi dicendo qualcosa di piu' puntuale. Che la dinamica del
singolo fotone e' probabilistica ma che riguarda fotoni individuali e
non un "campo" su cui si "sparpagliano" le proprietà del fotone.


Giorgio
Received on Fri May 19 2017 - 09:05:27 CEST