Dr. Arianna Borrelli


Dr. Arianna Borrelli

Arianna Borrelli is a historian and philosopher of natural philosophy and modern science. The subjects of her research range from medieval mathematical cosmology to quantum theories, passing through early modern meteorology and classical mechanics.

Born in Rome, she studied physics, philosophy and history of science in Italy and Germany and has held research positions in theoretical high energy physics and in the  history and philosophy of science at various European institutions.  



What is a particle? Computer simulations and the theoretical practices of early high-energy physics

Methods of computer-aided data analysis, including Monte Carlo simulations, were introduced into high-energy physics in the 1950s, and historian Peter Galison (1997) has studied their impact on experimental practices, showing how simulations came to be regarded as experiments in their own right. I shall investigate how these techniques shaped theoretical practices and, in particular, I will ask how they contributed to transform the notion of “particle” around 1960. It was at that time that a group of high-energy phenomena observed since the early 1950s and known as “resonances” came to be regarded by the physics community as “particles” in their own right.

This shift was not motivated by specific discoveries, but rather due to a change of perspective in the community: “Most of the objects labelled N*, the pion-nucleon resonances [...] were well known eighteenth months ago. The fact that they appear here along with the longer-lived particles reflects more a change in outlook by high-energy physicists than an increase in experimental knowledge.” (G. R., Lynch, “Experimental data on new resonances” 1962)

Indeed, until then the term “particle” had been reserved to those micro-physical entities which live at least long enough to leave tracks in detectors or trigger a counter. Instead, resonances are highly unstable constructs which cannot be detected directly and manifest themselves only as peaks or bumps in plots showing how the rate of a certain process varies with energy. From the 1960s onward, computer-aided data-analyses allowed to construct more and more of those plots, and soon resonances came to be referred to as a kind of particles. My working hypothesis is that in the scientific culture of the time the new computer-aided techniques (Monte Carlo simulations, best-fit procedures, numerical computations) came to be perceived as type of detector extending the human senses even further into the micro-physical realm, to make resonances visible - and thus eventually aiding them to “particle” status.

I plan to look closely at the historical sources relevant to this epistemic constellation, establishing which computer techniques were (or were not) involved in the shift, and how they role was discussed by physicists. This investigation is part of the DFG-funded project at which I am currently working at the TU Berlin and which bears the title: “Exploring the ‘dark ages’ of particle physics: isospin, strangeness and the formation of physical-mathematical concepts before the Standard Model  (1950-1965)“.