What is Life?

What Is Life? The Physical Aspect of the Living Cell is a 1944 science book written for the lay reader by the physicist Erwin Schrödinger. The book was based on a course of public lectures delivered by Schrödinger in February 1943, under the auspices of the Dublin Institute for Advanced Studies, where he was Director of Theoretical Physics, at Trinity College, Dublin. The lectures attracted an audience of about 400, who were warned "that the subject-matter was a difficult one and that the lectures could not be termed popular, even though the physicist’s most dreaded weapon, mathematical deduction, would hardly be utilized." Schrödinger's lecture focused on one important question: "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?"

In the book, Schrödinger introduced the idea of an "aperiodic solid" that contained genetic information in its configuration of covalent chemical bonds. In the 1940s, this idea stimulated enthusiasm for discovering the chemical basis of genetic inheritance. Although the existence of some form of hereditary information had been hypothesized since 1869, its role in reproduction and its helical shape were still unknown at the time of Schrödinger's lecture. In 1953, James D. Watson and Francis Crick jointly proposed the double helix structure of deoxyribonucleic acid (DNA) on the basis of, amongst other theoretical insights, X-ray diffraction experiments conducted by Rosalind Franklin. They both credited Schrödinger's book with presenting an early theoretical description of how the storage of genetic information would work, and each independently acknowledged the book as a source of inspiration for their initial researches.

The "What is life?" Lecture Series

What is Life? is based on the lecture series of the same name delivered in February 1943 under the auspices of the Dublin Institute for Advanced Studies (DIAS) at Trinity College, Dublin. The lectures were attended by the Irish Taoiseach (Prime Minister) Éamon de Valera and his cabinet. At that time, DNA was known to be a constituent of cell nuclei but had not yet been identified with certainty as the molecular basis of inheritance; the concept of a "heredity molecule" was strictly theoretical, with various candidates. One of the most successful branches of physics at that time was statistical physics. Schrödinger himself is one of the founding fathers of quantum mechanics, a theory which posits a statistical focus for understanding the natural world at subatomic scale.

In 1940, Éamon de Valera had invited Schrödinger to become the first Director of the School of Theoretical Physics at DIAS. Schrödinger, an Austrian physicist who had shared the Nobel Prize in Physics in 1933 for his development of wave-mechanics, had left Nazi Germany and, after sojourns at Oxford, Graz and Ghent, settled in Dublin for what became a sixteen-year tenure, the longest of his life. One of DIAS's statuary requirements was to organise an annual lecture series for a general audience. Schrödinger devised the 1943 series himself and delivered it at Trinity College Dublin (TCD).

Advertisment for the What is Life? Lectures.

Under the collective title “What is Life?”, Schrödinger presented three public lectures on consecutive Fridays (the 5th, 12th, and 19th) in February 1943 at TCD. The lectures were held in the Physics Lecture Theatre in the Fitzgerald building. By Schrödinger's accounting in What is Life?, the audience numbered about 400 for each lecture. As the Physics Lecture Theatre held only about 150, each lecture is thought to have been repeated on each of the following Mondays. The lectures were widely publicised in The Irish Times, and even received coverage in Time magazine in the U.S. Indeed, on February 6, 1943, The Irish Times published a photograph of Schrödinger with Dr Ernest Alton, Provost of Trinity, and Éamon de Valera standing outside the Physics Building at Trinity before the lecture.

Ernest Schrodinger with Eamon de Valera outside the Fitzgerald building in TCD before the first What is Life? lecture.

Schrödinger’s stated objective was to address the question: “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?” The subject matter was acknowledged in advance as difficult and not a popular science lecture in the usual sense. Schrödinger explored how physical concepts might underlie the stability of hereditary structures, mutation, and the organisation of living cells. He introduced the concept of the “aperiodic crystal” to describe the proposed hereditary material. He also argued that living systems are consistent with the laws of thermodynamics and compensate for the reduction in entropy associated with their growth by feeding on “negative entropy” from their environment. While the molecular mechanism of heredity in the form of DNA had not yet been discovered, in 1935 Nikolay Timofeev-Ressovsky, Karl Zimmer, and Max Delbrück had presented the first experimental evidence of a molecular basis of heredity at the Kaiser Wilhelm Institute for Chemistry in Berlin. Schrödinger knew Delbrück from his time in Berlin and was deeply intrigued by his experimental work; his speculations in Dublin brought attention to Delbrück's work and helped stimulate further inquiry.

What is Life? has been widely credited with influencing the young molecular biologists James D. Watson and Francis Crick, both of whom acknowledged his work as formative in their discovery of the DNA double helix in 1953. The Dublin Institute for Advanced Studies holds a 1953 letter from Crick to Schrödinger noting that he and Watson had been influenced by the book.

The lectures have been regarded as “the most important and exciting thing to happen in Trinity in all of the six dark years of wartime.” Time reported that “Only in the precarious peace of Eire could Europe today provide such a spectacle. At Dublin’s Trinity College last month crowds were turned away from a jampacked scientific lecture. Cabinet ministers, diplomats, scholars and socialites loudly applauded a slight, Vienna-born professor of physics. Erwin Schrödinger was speaking on the subject ‘What Is Life?’.”

Beginning in 1995 and continuing to this day, Trinity College has commemorated the original 1943 lecture series with an annual “What is Life?” lecture, usually delivered in the Physics Lecture Theatre. In 2018, Trinity also organised the 75th-anniversary conference “Schrödinger at 75: The Future of Biology”. The Trinity Library also produced an exhibition celebrating Schrödinger’s Dublin years and the impact of the lectures.