Q&A: James Owen Weatherall on the importance of nothing

There is a long tradition of physicists and philosophers arguing about nothing. And as physicist and philosopher James Owen Weatherall of the University of California, Irvine, shows in his new book, Void: The Strange Physics of Nothing, it’s been a productive conversation.

Void takes the reader on a journey through the history and philosophy of nothing—that is to say, the absence of matter—and explores the concepts of nothingness that were central to the work of figures such as Thomas Aquinas, Isaac Newton, and Richard Feynman. Weatherall argues that understanding how physical theories treat the concept of nothing sheds light on those theories’ descriptions of reality. In the September issue of Physics Today, reviewer Thomas Ryckman praises Weatherall’s “lively” volume and calls the book “a readable tour of how the physics of nothing has developed.”

Physics Today recently interviewed Weatherall about physics, philosophy, and the quirkiest ideas about nothingness.

PT: What inspired you to write a book about nothing?

WEATHERALL: The concept of nothing seems to me to be one of the places where physics makes direct contact with old, difficult philosophical questions: Why is there something rather than nothing? What are the fundamental natures of space and time? I argue in the book that we need to understand nothing to fully understand the structure of our physical theories, including Newtonian theories, Einstein’s general relativity, and modern particle physics. In all those theories, the meaning of nothing is deeply intertwined with what we mean by something.

The concept of nothing is very different in each of the theories I talk about, which shows how basic ideas that we think we understand can change dramatically once we put them to work in physics. It also shows how precise concepts can change as our theories change. One of the challenges facing physicists working on quantum gravity, I argue, is that there is a fundamental difference in how general relativity and quantum field theory understand nothing. One way to think about it is that in general relativity, nothing is a bit like a television screen that is turned off. In quantum field theory, it is a bit like a television that is turned on but not tuned to any station—you have lots of noise and random fluctuations. It’s hard to see how the noise you get in quantum field theory can be made compatible with the dynamics of general relativity.

PT: In the introduction to Void, you write that the way physical theories describe nothingness “goes right to the conception of reality that comes with these theories.” Can you give an example from the book to illustrate that idea?

WEATHERALL: One of the most interesting examples comes from general relativity. Space and time are curved, and that curvature is related to the distribution of matter in the universe. The curvature is described by the fundamental equation of the theory, which is known as Einstein’s equation. But it turns out that there is a whole bestiary of solutions to Einstein’s equation, representing possible universes allowed by the theory, in which there is no matter. These are known as vacuum solutions, and it turns out that they can describe all sorts of phenomena that we might have thought of as stuff, such as black holes and gravitational waves. Understanding how a black hole can count as nothing reveals how powerful the idea of spacetime curvature is, which in turn provides a lot of insight into how general relativity explains phenomena we observe in our own universe. It also shows how blurry the distinction between something and nothing has become in modern physics.

PT: Void includes a number of historical figures. Who do you think had the most interesting or strangest concept of nothing?

WEATHERALL: I think the strangest concept, by a long shot, is that associated with quantum field theory, which was first developed in the 1930s and 1940s by a number of physicists, including Feynman, Paul Dirac, Julian Schwinger, and Freeman Dyson. In quantum field theory, nothingness, or at least the closest we get to it, is described by something called the quantum vacuum. That represents a situation in which, if you measured the total number of particles in the entire universe, you would be certain to measure zero. But the quantum vacuum has all sorts of strange properties. For instance, it is often said to fluctuate, which means that it is possible for pairs of particles to pop in and out of existence. Those ethereal particles turn out to have observable significance—for instance, in a phenomenon known as the Lamb shift, wherein the spectral properties of hydrogen are influenced by vacuum fluctuations.

PT: You began your academic career with a double major in physics and philosophy. What led you to pursue the philosophy of physics?

WEATHERALL: I have loved physics and mathematics since I was a kid. I was very lucky to have terrific physics teachers in high school and as an undergraduate, and for the first year or two of college I majored in physics only. But I had some close friends who were philosophy majors, and I found myself increasingly drawn to the sorts of questions that philosophers ask—not about physics per se, but more generally. In retrospect, I had a very narrow conception of what philosophy of physics was all about. That changed when I took a wonderful course with Peter Galison, who is a very distinguished historian and philosopher of physics. After that I was hooked. I wrote an undergraduate thesis in philosophy of physics, and then I pursued philosophy in graduate school even as I continued doing work in physics.

PT: What are you reading?

WEATHERALL: I’ve been spending a lot of time with Merchants of Doubt by Naomi Oreskes and Erik Conway, who are both historians of science. It is an excellent, fascinating history of how a small group of physicists has influenced public policy on a range of health and environmental issues over the last 40 years, from the ozone hole to secondhand smoking and ultimately climate change. I am about to start Craig Callender’s newest book, What Makes Time Special.

PT: What is your next project?

WEATHERALL: I am writing a book with Cailin O’Connor, a philosopher of biology and an evolutionary game theorist, on the social dynamics of false belief. We are taking models and ideas originally developed by economists and philosophers of science to understand how social effects influence scientific communities. Then we’re applying those ideas to the question of why falsehoods can persist and spread even when there is strong contrary evidence available. It is a mix of history and philosophy of science, but with the current political climate in the US very much in view.