(Roughly) Daily

… But what is gravity? George Musser unpacks a new argument that explores how the growth of disorder could cause massive objects to move toward one another– one that has left some physicists interested, and some skeptical…

Isaac Newton was never entirely happy with his law of universal gravitation. For decades after publishing it in 1687, he sought to understand how, exactly, two objects were able to pull on each other from afar. He and others came up with several mechanical models, in which gravity was not a pull, but a push. For example, space might be filled with unseen particles that bombard the objects on all sides. The object on the left absorbs the particles coming from the left, the one on the right absorbs those coming from the right, and the net effect is to push them together.

Those theories never quite worked, and Albert Einstein eventually provided a deeper explanation of gravity as a distortion of space and time. But Einstein’s account, called general relativity, created its own puzzles, and he himself recognized that it could not be the final word. So the idea that gravity is a collective effect — not a fundamental force, but the outcome of swarm behavior on a finer scale — still compels physicists.

Earlier this year, a team of theoretical physicists put forward what might be considered a modern version of those 17th-century mechanical models. “There’s some kind of gas or some thermal system out there that we can’t see directly,” said Daniel Carney of Lawrence Berkeley National Laboratory, who led the effort. “But it’s randomly interacting with masses in some way, such that on average you see all the normal gravity things that you know about: The Earth orbits the sun, and so forth.”

This project is one of the many ways that physicists have sought to understand gravity, and perhaps the bendy space-time continuum itself, as emergent from deeper, more microscopic physics. Carney’s line of thinking, known as entropic gravity, pegs that deeper physics as essentially just the physics of heat. It says gravity results from the same random jiggling and mixing up of particles — and the attendant rise of entropy, loosely defined as disorder — that governs steam boilers, car engines and refrigerators.

Attempts at modeling gravity as a consequence of rising entropy have cropped up now and again for several decades. Entropic gravity is very much a minority view. But it’s one that won’t die, and even detractors are loath to dismiss it altogether. The new model has the virtue of being experimentally testable — a rarity when it comes to theories about the mysterious underpinnings of the universal attraction…

[Musser explains the hypothesis, traces is origin, and reviews other scientists’ reactions, and traces possible approaches to testing it…]

… if this long-shot theory does work out, physicists will need to update the artist Gerry Mooney’s famous gravity poster, which reads: “Gravity. It isn’t just a good idea. It’s the law.” Perhaps gravity is not, in fact, a law, just a statistical tendency…

“Is Gravity Just Entropy Rising? Long-Shot Idea Gets Another Look” from @georgemusser.com‬ in @quantamagazine.bsky.social‬.

* Gerry Mooney

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As we fumble with forces, we might send insightful birthday greetings to a man who encourages us to see in different ways, M. C. Escher; he was born on this date in 1898. A graphic artist inspired by mathematics, he created woodcuts, lithographs, and mezzotints, that— while largely ignored by the art world in his lifetime, have become widely celebrated. He’s been recognized as an heir to Parmigianino, Hogarth, and Piranesi.

His work features mathematical objects and operations including impossible objects, explorations of infinity, reflection, symmetry, perspective, truncated and stellated polyhedra, hyperbolic geometry, and tessellations. And though Escher believed he had no mathematical ability, he interacted with the mathematicians George Pólya, Roger Penrose, and Donald Coxeter, and the crystallographer Friedrich Haag, and conducted his own research into tessellation.

For more on (and more examples of) Escher’s work, see here.