Céline Boisserie-Lacroix

Quantum diffractions

First impressions

About ten years ago, I was studying experimental sciences at ESPCI. I remember being troubled when realizing that scientific theories and experiments have a form, and that this form is particularly beautiful. This wonder was all the more intense because the world I was discovering is not our ordinary world. The world of experimental science is composed of objects such as “interference fringes”, “crystalline networks”, “precipitates”, and many others. The laboratory appeared to me as a cabinet of curiosities inhabited with glassware of strange shapes and futuristic electronic devices.

It was possible to take an introductory course in quantum physics, and I enrolled. This concise language, populated with complex mathematical equations, doubled by practical work with enigmatic titles, sparked in me a rage to understand. In a room cluttered with machines, we were asked to delve into the fluctuations of the vacuum. In a recently published essay, philosopher Joëlle Zask reminds us that “nature surpasses imagination, even the wildest one”1, and it is an infra-material imagination that unfolded before our eyes. Traversed by micro-changes, imbued with unsuspected qualities, the vacuum described by quantum physics seemed to acquire a poetic status.

Foundational Disorientations

Yet, is it really the beauty of the quantum world that immediately strikes those who encounter it? Mathematicians readily speak of the beauty of their theories. Upon closer inspection, this beauty surprises. It seizes the one who apprehends it, like a “strange bewilderment”, a “sudden disorientation”2. Highly mathematized, quantum physics could evoke this kind of confused vertigo among physicists. Diving into its beginnings justifies these theoretical disorientations. Physicist Carlo Rovelli states that “there is no emotion comparable to that of glimpsing a mathe-matical law behind the disorder of appearances”3, and quotes Werner Heisenberg. “Deeply troubled” by the discoveries he made on the island of Helgoland in June 1925, this founding father of theoretical physics declared having had “the sensation of looking, through the surface of phenomena, into an interior of strange beauty”.

This disconcerting nature of quantum theory reflects the upheaval it has induced in our way of envisioning reality. Niels Bohr, another of its creators, proposed a classical interpretation of quantum formalism, known as the Copenhagen inter-pretation, according to which, surprisingly, experimental measurements have an impact on the observed objects. This observation fundamentally distinguishes the quantum world from the classical world, where this “measurement problem” does not arise. Classical epistemology, which relies on the presence of a neu-tral, detached observer, is undermined, while the conditions for the possibility of objective knowledge must take into account the set formed by the observer (the scientist), the observed object (the particle), and the measuring apparatus.

More recently, physicist and philosopher Karen Barad has developed a “rela-tional ontology” based on his thought, incorporating contributions from critical