A scientist is supposed to write within his field of expertise as a matter of noblesse oblige, writes Erwin Schrödinger, one of the architects of modern quantum science, in his 1944 book What Is Life?. “I beg to renounce the noblesse,” he writes next, inviting the reader into the realm of living organisms instead of the inanimate atoms that he had made a name for himself studying. For 90 or so pages, he is ready to give up his position among the greats of one science and join the rest of us strivers and dabblers in developing new, and somewhat naïve, ideas about another. In doing this, he produced one of the most influential popular-science books of the 20^th century.

Based on a series of lectures that Schrödinger gave in Dublin in 1943, What is Life? is both short and conversational, not shying away from the occasional self-effacing remark or a poetic turn of phrase. Yet Schrödinger’s framing of the book’s central problem is stated firmly in the language of physics: “How can the events in space and time which take place within the spatial boundary of a living organism be accounted for by physics and chemistry?”

To arrive at an answer, he is also thinking like a physicist. Accordingly, What is Life? – subtitled The physical aspect of the living cell – starts with the discussion of how small and numerous the building blocks (such as atoms) of any living organism are, and how they should consequently obey the laws of statistical physics. Schrödinger is on solid ground here and can clearly articulate how, when a physicist considers a large collection of tiny things, they can say something about them on average, but not about any single one of them exactly.

The laws of physics also dictate that such systems constantly evolve towards increasing disorder, and that they are filled with fluctuations. But living organisms are neatly ordered, prompting the very intrigued Schrödinger to compare them to the intricate inner mechanisms of clocks. They can also reliably reproduce and pass on their traits thanks to a very small amount of “hereditary substance” – a point that baffles him.

What Is Life? was written before the structure of DNA was fully understood, so Schrödinger is unsure what this substance is made up of, but he draws on studies of the heredity of radiation-induced mutations and even connects them to “quantum jumps” from his domain of expertise. He ruminates on what kind of solid this hereditary substance could be and how quantum theory could explain some of its stability. His other major hypothesis is that a living organism needs “negative entropy” – to escape always eventually becoming disordered, it must be “continuously sucking orderliness from its environment”. How exactly does all this come together? Schrödinger posits that we may need new laws of physics to fully answer that question.

Upon its publication in 1944, What is Life? was incredibly influential, and is reported to have inspired several physicists to turn to biology. Popular audiences read it, and kept reading it, too, so the book routinely makes “best of” lists. But chemists and biologists received it less warmly.

Nobel laureate Max Perutz wrote about the ample amount of contemporaneous research that Schrödinger could have read to find answers to some of his questions. For example, his bafflement at how a tiny piece of hereditary substance in a cell can be reproduced during cell division without being destroyed by fluctuations could have been avoided by better understanding ideas around enzymes that participate in this process. Pertuz also criticised the idea of negative entropy.

More recently, writer Philip Ball noted that Schrödinger could have understood this concept more had he engaged with ideas that connect entropy and information, for instance Leo Szilard’s 1929 resolution to the famous Maxwell’s demon paradox, where the rise of disorder also seemed to be mysteriously stymied.

Despite those very valid criticisms, What is Life? still feels prescient in 2026. As a former physicist, I am probably a more sympathetic reader than someone who lives and breathes the ins and outs of modern genetics. But whenever I have interviewed biophysicists, I have also heard echoes of What is Life? in their words. Just last year, a researcher told me about the long-term prospect of formulating a new law of physics for living matter. Another alerted me to the words of physicist Philip Pincus at the University of California, Santa Barbara: “If you’re in equilibrium, you’re dead.” That is exactly what Schrödinger was thinking through in the 1940s!

In 2021, biophysicist Rob Phillips at the California Institute of Technology argued that What is Life? is best read as “a manifesto about the frontiers of physics and the way that every time physics tackles new classes of phenomena, it requires new concepts and ultimately results in the formulation of new laws”. I am inclined to agree. Schrödinger’s grasp of biology and chemistry is imperfect at best, but his physicist’s intuition has stood the test of time.

Will physicists ever be the right people to spell out the exact mechanism by which something is alive, instead of being an inanimate pile of atoms? This is a question for philosophers of science, but also one that research conducted in the coming years could really illuminate. This is as exciting as it is infuriating, a sentiment that Schrödinger not just captured, but tried to tackle more than 80 years ago.