Delivered at Trieste on the occasion of the 25th
Anniversary of the International Centre for Theoretical Physics, 2 November 1989
The video of this lecture is available here. Please see the PDF for the transcript of the lecture.
General remarks by Angelo Bassi and GianCarlo Ghirardi
During the autumn of 1989 the International Centre
for Theoretical Physics, Trieste, celebrated the 25th
anniversary of its creation. Among the many prestigious speakers,
who delivered extremely interesting lectures on that occasion,
was the late John Stewart Bell. All lectures have been
recorded on tape. We succeeded in getting a copy of John's lecture.
In the lecture, many of the arguments that John had lucidly stressed
in his writings appear once more, but there are also extremely
interesting new remarks which, to our knowledge, have not been
presented elsewhere. In particular he decided, as pointed out by the
very choice of the title of his lecture, to call attention to the
fact that the theory presents two types of difficulties, which Dirac
classified as first and second class. The former are
those connected with the so-called macro-objectification problem,
the latter with the divergences characterizing relativistic quantum
field theories. Bell describes the precise position of Dirac on
these problems and he stresses appropriately how, contrary to
Dirac's hopes, the steps which have led to a partial overcoming of
the second class difficulties have not helped in any way whatsoever
to overcome those of the first class. He then proceeds to analyse the
origin and development of the Dynamical Reduction Program and draws
attention to the problems that still affect it, in particular that
of a consistent relativistic generalization.
When the two
meetings Are there quantum jumps? and On the present status of
Quantum Mechanics were organized in Trieste and Losinj
(Croatia), on 5–10 September 2005, it occurred to us that this lecture,
which has never been published, might represent an extremely
interesting historical record for all the participants who certainly
shared with us a great admiration for this outstanding scientist
and deep thinker. Accordingly, with the permission of the Abdus Salam
International Centre for Theoretical Physics, and with thanks to the
financial support of the Consorzio per la Fisica of the Trieste
University, we have produced from the original record a DVD which
has been given to all participants although, unfortunately, the video tape of
the event was not particularly good.
Taking into account that the
participants to the meetings represented only a very small subset of
those scientists
who might be interested in hearing what John Bell said in
probably his last lecture, we considered that it would be useful for the
scientific community interested in foundational problems to publish
the text of this lecture in order to make it accessible to
everybody. The lecture was preceded by a presentation by the
Chairman, Alain Aspect, which we have also included.
Due to the aforementioned low quality of the recording it
has not been easy to pass from the tape to the text we are
presenting below, and we have to thank, for her precious
collaboration, Dr Julia Filingeri who did most of the work, as well
as Mrs Anne Gatti from ICTP, Professors Detlef Düurr and Sheldon
Goldstein, and the staff of IOP Publishing who contributed in an essential
way in deciphering some
particularly difficult passages. Obviously, we take full
responsibility for any possible inappropriate rendering of the
original talk. We thank the
Abdus Salam International Centre for Theoretical Physics for
authorizing IOP Publishing to publish this important document.
Some final
remarks are in order. Firstly, we have put in
square brackets parenthetical remarks that John made while reading
sentences from his transparencies. We have also indicated by
parenthetical ellipsis (...) very short parts of the speech (usually one
word) which we have not been able to decipher. We have included a
picture (figure 1) shown by him, taking it from the tape image which is
of rather poor quality (we apologize for this) and three figures taken from his
transparencies. Moreover, to help the reader in grasping the various
points John Stewart Bell brilliantly raised in his talk we have divided
the paper into six sections whose titles have been chosen by us to
summarize the most crucial points of his argument.
Presentation by the Chairman, Alain Aspect
It is a great pleasure and an honour to introduce Professor Bell.
When looking to my old papers I discovered that this 25th
anniversary of the ICTP also coincides with the famous paper in
which appeared, for the first time, inequalities that are now known
as Bell's inequalities so it's a very good opportunity to have a
talk by John Bell here. Many of us have been strongly influenced by
this work of John Bell because he has shown us that
quantum mechanics is much more difficult to understand that we
thought it was. I am sure that today he will again raise some
questions which are very embarrassing but that we have definitely to
face.