Johns Hopkins Natural Philosophy Forum

Seminar: Heather Demarest
2025-11-05 16:00 - 17:30 (America/New_York) | 217 Maryland Hall, Johns Hopkins University, Baltimore, MD, 21218, United States
Heather Demarest is a professor of philosophy at the University of Colorado, Boulder.
Title: “Macrostates, Natural Kinds, and Statistical Mechanics”
Abstract: The second law of thermodynamics states that entropy (almost) always increases over time. However, different systems do this in very different ways. In some systems, like boxes of gas, entropy increases smoothly and uniformly. In other systems, such as refrigerators, crystals, trees, zebras, and human brains, entropy decreases in parts of the system, while increasing in other parts. A zebra (together with its environment) does not violate the second law, but there is an important sense in which the zebra resists (or perhaps more accurately, exploits) the second law. The zebra maintains or reduces its entropy by shunting its extra entropy into its environment. This is possible because the zebra consumes highly ordered, low-entropy energy (grass) and excretes higher entropy waste (heat and manure). In this paper, I defend a metaphysical account of this difference in terms of multiple realizability—the fewer microphysical realizers a kind has, the more it is able to resist the second law. I make this notion precise with functional information (Hazen 2007; Wong 2023) of macrostates in the phase space of statistical mechanics.

Fourth Annual Distinguished Lecture: P. James Peebles
2026-03-10 17:00 - 19:00 | 272 Bloomberg Center for Physics & Astronomy, 3701 San Martin Dr, Baltimore, MD, 21218, United States
P. James Peebles, Princeton University.

The Physicists’ Philosophy of Physics
Abstract:
I will argue that physicists share an implicit but well-defined way of thinking that amounts to a philosophy, though one that I expect is more tightly prescriptive than many discussed by real philosophers. The physicists’ philosophy differs from that of the other natural sciences by its reliance on tests of reliable predictions of theories that we think are useful approximations to our notion of reality. I will offer examples of applications of this philosophy to the small scales of quantum physics and the large scales of cosmology. Both physics pass demanding tests that establish them as useful approximations to our reality, but they are not consistent. It can be compared to Snow’s two cultures. The two cultures differ more broadly than the two physics, but they share the separating effects of different working conditions. It’s difficult to imagine that someone capable of creating a notable history of philosophy could make significant contributions to physics. It’s easier to imagine someone making key contributions to small-scale and large-scale physics, but I cannot think of anyone who managed it in the past century or two. The two cultures and two sciences might profit by closer interactions.
The lecture will be held at 5:00pm in the Schafler Auditorium (room 272), Bloomberg Center for Physics and Astronomy
(note: not the Bloomberg Student Center)
