Column: At the corner of life, the universe, and everything

I don’t remember much about my first undergraduate class in classical mechanics. But I remember the unusual way the professor once defined physics: as “the study of the universe and everything in it.” Is there anything that wouldn’t be covered by that definition? The Napoleonic Wars, the composition of Jane Eyre, and the Trump administration’s attack on the US Postal Service are all things that have happened in the universe. Their study, apparently, would count as physics.

In my professor’s defense, he was being slightly tongue-in-cheek. He was offering the definition as part of his argument against the still too common idea that certain segments of the population—you know which ones—just aren’t interested in physics, so it’s no big deal if they’re not well represented among physicists and physics students. But if physics is the study of everything there is, it seems awfully unlikely that entire demographic groups could fail to find anything that interests them in it—unless, of course, they are actively encouraged not to.

Alas, I’ve known people to seriously adopt my professor’s all-encompassing view, without any of the noble context. As a grad student, I flitted between the physics and chemistry departments before deciding, at least temporarily, that I felt more at home in the latter. Some of my physics colleagues thought I’d opted for the clearly inferior field. “We can just derive it all,” they told me.

I would have liked to see them try. It’s true that most of the complexity of chemistry stems from only a little physics: just charged particles and quantum mechanics. But the Schrödinger equation lacks an exact solution for just about anything more complicated than a hydrogen atom. And solving it approximately requires some careful thought about how to make the approximations to preserve a system’s important features—which requires an understanding of what those features are.

Miller’s Diary

Physics Today editor Johanna Miller reflects on the latest Search & Discovery section of the magazine, the editorial process, and life in general.

Furthermore, even if physics could derive with certainty the outcome of one bunch of atoms interacting with another, it wouldn’t necessarily be able to say much about what that interaction means. It wouldn’t have the language to describe how different bunches of atoms behave similarly to one another—the words for acids, bases, nucleophiles, electrophiles, aldehydes, ketones, and so forth—unless someone invented it. And by the very act of inventing it, they’d be doing chemistry, not physics.

Likewise, Napoleon Bonaparte, Charlotte Brontë, and Postmaster General Louis DeJoy are also bunches of atoms governed by quantum mechanics. But even if their trajectories could be computed with any meaningful accuracy, the analysis couldn’t identify certain movements of atoms with the Battle of Waterloo, the character development of a romantic heroine, or the integrity of a presidential election—and if it could, it would be history, literary analysis, or political science, not physics.

Viewed that way, chemistry and physics are separate disciplines not because of which objects they study but because of how they study them: Which features of a system, on which level of complexity, are worth talking about?

The August issue of Physics Today contains two otherwise unrelated pieces relevant to the question of where physics ends and another discipline, in this case biology, begins. The first is a feature article by Paul Davies that asks whether new physics lurks in living matter. Davies postulates that biology, like chemistry, can be distinguished from physics by its difference in language and conceptual framework—where physicists talk about the flow of matter and energy, biologists talk about the flow of information—and that merging those worldviews can lead to new insights that neither alone can provide. (Davies seems happy to call the merged science “new physics” rather than “new biology” or something else entirely.)

The second is a story I wrote for Search & Discovery on work toward a new blindness treatment that combines nanoscience and gene therapy. It’s about as far from pure physics as I’ve ever ventured in Physics Today. The research paper, which appeared in Science, is classified there as neuroscience, and it’s mostly about the intricacies of proteins, genes, neural connections, the anatomy of the retina, and experiments on mice.

But at the heart of what the researchers accomplished, there’s a story to be told in physics language: They connected nanoparticles, proteins, and neurons so that a nanoparticle absorbs near-IR light and transfers heat to a protein, which triggers an electrical signal to be sent to the brain. That’s a brand-new energy pathway not naturally active in mammalian eyes, and mice thus treated can see at a wavelength they normally can’t. More than just a fun superpower, the wavelength workaround is important because it keeps the artificially endowed vision from clashing with any remaining natural vision. If developed into a safe and effective treatment for humans, it could change the lives of millions of people with progressive vision loss that’s debilitating but not yet complete.

The question of what is or isn’t physics comes to a head for us every October when the Nobel Prizes are announced. We always cover the physics prize, of course, and we cover either or both of the other science prizes whenever there’s enough of a physics connection for us to report. Sometimes that connection is obvious, as it was in 2014, when the chemistry prize was awarded for superresolution microscopy , a collection of imaging techniques that overcome what seems at first to be a fundamental limit of optics. It was clear last year as well, when it was awarded for lithium-ion batteries , which have revolutionized energy storage.

The 2018 chemistry prize, on the other hand, presented us with a more difficult decision. It was awarded for research in directed evolution: transforming proteins found in nature to perform new functions through successive rounds of mutation, recombination, and selection. At first the prizewinning work seems unrelated to physics; one of my colleagues thought we should skip it on the grounds that the early radio reports kept using the words test tube. I was of the opposite opinion: Frances Arnold, one of the laureates, had come to my attention two years earlier for her development of an enzyme that could create a carbon–silicon chemical bond, a type of interface between the organic and inorganic worlds that exists nowhere in nature. From that angle alone, it seemed like there must be a physics story to tell.

In the end, we covered the prize, and I’m glad we did. Physics and evolution are connected in more ways than I’d realized, and I’m not sure my story does them all justice. (Also, Arnold herself is a very impressive person, and the scientific community is better off because she found something in the universe to be interested in.)

According to its mission statement, the American Institute of Physics (which publishes Physics Today) exists to “advance, promote, and serve the physical sciences,” and “physical sciences” is deliberately left undefined. The dictionary definition—the sciences concerned with nonliving matter, as distinct from the life sciences—doesn’t suffice. However you draw the disciplines’ boundaries, there’s a lot of physics to be found in living things.