Berkeley researcher, John Cardy awarded 2024 Breakthrough Prizes where his quantum theory touches a good explanation on how grind coffee drips through a narrow filter

September 25 - 2023

Coffee Geography Magazine

The Breakthrough Foundation announced its 2024 Laureates, recognizing John Cardy,a Berkeley researcher affiliated with the Division of Mathematical and Physical Sciences. Renowned as the ‘Oscars of Science,’ the Breakthrough Prizes recognize “the world’s top scientists” in the fields of life sciences, fundamental physics and mathematics. Now in its 12th year, the Breakthrough Prizes also honor early-career researchers with a New Horizons Prize in Physics, New Horizons Prize in Mathematics, and the Maryam Mirzakhani New Frontiers Prize. This year’s prize money totals $15.75 million, and the laureates will be celebrated on April 13 at a star-studded event in Los Angeles.

Cardy, an Emeritus Fellow at All Souls College, University of Oxford, was named a co-recipient of the 2024 Breakthrough Prize in Fundamental Physics. Cardy was a senior researcher for many years at UC Berkeley. Focusing his work on quantum field theory, he published several papers during his tenure. He and co-winner Alexander Zamolodchikov (Stony Brook University) were cited for “profound contributions to statistical physics and quantum field theory, with diverse and far-reaching applications in different branches of physics and mathematics.”

Conformal field theory acts as a bridge between different fields of physics: the underlying math is used in string theory, condensed matter physics and quantum statistical mechanics. Cardy’s formulas can describe the entropy of certain kinds of two-dimensional black holes that are used as models of the real thing. They can describe how fluids move through networks of pores when new nodes are added. This explains quantitatively why morning coffee takes longer to percolate through a tall, narrow filter than a short, wide one, but it also has a lot of implications for fundamental physics.

But the kind of quantum field theories that were dealt with aren’t the weakly interacting kinds that people had looked at in previous contexts. [Weak and strong interactions are two fundamental forces in physics. Strong attractions hold together subatomic particles such as protons and neutrons, and weak interactions govern radioactive decay.] One had to somehow develop the kinds of mathematics that could treat the system as a whole as strongly interacting.

Instead of temperature, the control parameter is the proportion of pores that are open. Each pore is open with probability p and closed with probability 1 – p independently. If p is small, the fluid doesn't flow through the network; if p is close to 1, it does. Somewhere in between is a critical value, called the percolation threshold, at which the fluid begins to flow all the way across the network. It turns out that the percolation threshold is analogous to the critical temperature. In a wider filter, there are more potential paths for the fluid to take. If it is taller, however, each path has to go farther.

The mathematicians were not happy about Cardy’s nonrigorous arguments, however. A different group developed a different approach called Schramm–Loewner evolution (SLE), which describes the actual path that the fluid takes as it percolates through the network. After a lot of mathematics, this reproduces his formula and gives many other results.

“We take great pride and are deeply honored to have this extraordinary talent as part of our Berkeley community,” said Steven Kahn, Dean of the Division of Mathematical and Physical Sciences in UC Berkeley’s College of Letters & Science. “John Cardy was a cherished colleague during his tenure as a senior researcher here. His Breakthrough Prize comes as no surprise, as John's work has made an enduring impact and continues to inspire generations of scientists.”