I was at the École de Physique, in Geneva, in the years 1989-1991, and got to interact on a daily basis with Constantin Piron, when I started a doctoral thesis with him. I have many souvenirs of Constantin’s colorful personality and original mind.
When he hired me, I still remember very well when he told me, in an extremely serious tone, that the job of a theoretical physicist did not entail particular risks in terms of accidents at work, with the exception maybe of that of losing one’s reason!
For a while, he convinced me to share the office with his wife Armelle, as he didn’t want me to stay with the other graduate students (who were located in another building), otherwise they would have influenced and corrupted my young mind with their misconceptions about quantum mechanics and relativity theory.
Discussing with him was always extremely challenging, as he had original ideas on almost every topic. Just to give an example, I remember that when I mentioned him my allergy to pollen, after looking at me in a fatherly way, he smiled and said: you know, maybe you should just not believe in your allergy, go to a field full of the pollen you pretend to be allergic to, take many deep breaths, and everything could be over after that…
Constantin’s mood was extremely unpredictable, like a quantum phenomenon. For example, when I had to go to his office, I never knew if he would welcome me gracefully, as he sometimes used to do, or if he would scold me for my disturbance. And I also remember that all the people I met, who have interacted with him in depth, remained in a sort of love-hate superposition state, without ever managing to disentangle the dilemma.
At that time, I was the assistant for his famous course in quantum mechanics. His approach to quantum mechanics was an operational and realistic one, and the (counterfactual) Einstein-Podolsky-Rosen reality criterion played an important role in it. To stress its importance, Constantin loved to remind his students, particularly when he was writing at the blackboard, to not confuse a broken chalk with a breakable chalk! Good chalks are breakable, he used to say with conviction, and one must take care not to break them unnecessarily.
The time that he really surprised me, was when he once took a 10 francs bill from his wallet and torn it in half, in front of a class of stunned students. He would then move the two halves along different trajectories, to finally bring them back again together, in his wallet, to show that the “10 francs entity” is able to behave in a way that is very similar to a quantum entity, as in a sense the 10 francs can be simultaneously present in different locations, without being actually present in any of them.
I never completed my thesis with Constantin, as at some point I decided to work on a different subject, with Philippe Martin, a friend of him and also a student of Josef Maria Jauch. When I left Geneva, Constantin was palpably not very happy with my decision, as it meant that our scientific collaboration kind of failed. But for sure, my interaction with him deeply marked my future way of doing and understanding physics.
In a sense, I remained connected with him “at a distance,” as many decades later I came into contact with one of his most brilliant students, Diederik Aerts, who took over the legacy of the Geneva school and brought it to a new phase of important developments and discoveries. With Diederik I am today collaborating on many of the themes who were at the heart of Constantin’s reflections, and I like to believe that, seeing the results we have obtained, in the ambit of what is today called the Geneva-Brussels school of quantum mechanics, he would be very happy with it.
P.S.: in the photo, professors Werner Amrein (left, who was one the examiners of my PhD thesis), Constantin Piron, at the center, and Josef Maria Jauch, here in the seventies, in Varenna (Italy).
Massimiliano Sassoli de Bianchi – Center Leo Apostel – Brussels Free University