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Erwin Schrödinger (1887–1961)

Schrödinger was a physicist whose career produced two bodies of work with influence in entirely different domains. The first was wave mechanics: the Schrödinger equation (1926), one of the foundational equations of quantum mechanics, which describes how the quantum state of a physical system evolves over time. The second was a short book, What is Life? (1944), which asked what physics could say about living organisms — and whose answer, that life maintains itself by feeding on “negative entropy,” shaped the thinking of a generation of physicists-turned-biologists who went on to found molecular biology.

Life

Born 12 August 1887 in Vienna, Austria-Hungary. His father Rudolf was a botanist and oilcloth manufacturer; his mother Georgine came from a family of chemists. Educated at the Akademisches Gymnasium in Vienna, then the University of Vienna, where he studied under Franz Exner and Friedrich Hasenöhrl. PhD in physics (1910). Served as an artillery officer in the First World War on the Italian front.

Academic positions at Jena, Stuttgart, Breslau, and Zurich. The Zurich period (1921–27) was the most productive: the wave equation was developed there in an extraordinary burst of work in early 1926. Succeeded Max Planck at the University of Berlin (1927). Left Germany in 1933 when the Nazis came to power — not Jewish, but unwilling to work under the regime. Fellow at Magdalen College, Oxford (1933–36). Nobel Prize in Physics (1933, shared with Paul Dirac). Moved to the University of Graz (1936). After the Anschluss (1938), he published a conciliatory statement to the Nazi authorities in an attempt to keep his position — a letter he later regretted and apologised to Einstein for. The attempt failed; he fled Austria shortly after. Spent the remainder of his career at the Dublin Institute for Advanced Studies (1940–56), invited by Éamon de Valera. Returned to Vienna in 1956. Died 4 January 1961 in Vienna, aged seventy-three.

Wave mechanics

In early 1926, Schrödinger published a series of papers — “Quantisierung als Eigenwertproblem” (“Quantisation as an eigenvalue problem”) — that reformulated quantum mechanics as a wave equation. Where Heisenberg’s matrix mechanics (1925) described quantum systems through discrete, algebraic operations on observable quantities, Schrödinger’s approach described them as continuous wave functions evolving in time according to a differential equation.

The Schrödinger equation — iℏ ∂ψ/∂t = Ĥψ — gives the time evolution of the wave function ψ, where Ĥ is the Hamiltonian operator representing the system’s total energy. The approach was immediately successful: Schrödinger used it to derive the energy levels of the hydrogen atom, matching the known spectral lines.

The two formalisms — Heisenberg’s matrices and Schrödinger’s waves — were quickly shown to be mathematically equivalent (Schrödinger himself demonstrated this in 1926; von Neumann later unified them in a Hilbert-space framework). The physical interpretation was more contentious. Schrödinger initially hoped the wave function described a real, physical wave in space. Max Born’s probability interpretation (1926) — that the square of the wave function’s amplitude gives the probability of finding a particle at a given location — prevailed, but Schrödinger never fully accepted it. His later “cat” thought experiment (1935) was designed to show that the Copenhagen interpretation of quantum mechanics leads to absurd macroscopic consequences — a cat simultaneously alive and dead — not as a celebration of quantum weirdness but as a critique of the prevailing interpretation.

The equation is time-symmetric: it works equally well run forwards or backwards. This places it alongside Newton’s laws and Einstein’s field equations as one of the fundamental equations of physics that do not distinguish past from future — the arrow of time is not in the equation but in the statistical mechanics built on top of it.

What is Life?

What is Life? The Physical Aspect of the Living Cell (Cambridge, 1944). Based on lectures delivered at Trinity College Dublin in February 1943.

Schrödinger asked: how does a living organism maintain its organisation against the tendency toward equilibrium? The second law of thermodynamics says that entropy increases in isolated systems — disorder grows. Yet living organisms sustain highly ordered structures for the duration of their lives. How?

His answer: an organism “feeds on negative entropy.” It imports low-entropy energy from its environment (food, sunlight) and exports high-entropy waste (heat, metabolic by-products). The organism maintains its internal order by continuously processing free energy — it stays far from equilibrium not by violating the second law but by being an open system coupled to an energy source.

The concept was not entirely new — statistical mechanics had the tools — but Schrödinger’s framing made it vivid and accessible to a generation of physicists looking for problems beyond their own discipline. The book also proposed that genetic information must be stored in an “aperiodic crystal” — a molecule whose irregular but non-random structure carries a code. This anticipation of the molecular nature of the gene was widely cited by the founders of molecular biology. Francis Crick, James Watson, and Maurice Wilkins each credited What is Life? as formative; Crick noted that the book “looked at the problems of biology in terms of atoms and molecules.”

The book’s influence was less in its specific claims (the “negative entropy” concept was imprecise — Léon Brillouin and others later clarified the relationship between entropy and information) than in the question it posed: can a physicist’s framework illuminate biology? The question drew physicists into biology and contributed to the intellectual conditions that produced molecular biology.

Where Schrödinger stops

Schrödinger’s question in What is Life? — how does an organism maintain its order? — is a physicist’s question addressed to biology. The answer (negative entropy, open systems, free-energy processing) identifies the thermodynamic conditions that life requires but does not address how living systems achieve what they achieve: how genetic information is encoded, how it is read, how development produces form, how evolution generates novelty. The thermodynamic framing establishes a necessary condition for life — an entropy gradient — without addressing the biological mechanisms that exploit it. Prigogine’s dissipative structures later formalised the far-from-equilibrium dynamics; molecular biology supplied the mechanistic detail. Schrödinger posed the question at the right level of generality; the answers came from other programmes.

Key works

Schrödinger, E., “Quantisierung als Eigenwertproblem,” Annalen der Physik 79–81 (1926) — the wave equation, four papers
What is Life? The Physical Aspect of the Living Cell (Cambridge, 1944) — negative entropy, the aperiodic crystal, the physicist’s question to biology
“Die gegenwärtige Situation in der Quantenmechanik” (“The present situation in quantum mechanics”), Naturwissenschaften 23 (1935) — the cat thought experiment
Nature and the Greeks (Cambridge, 1954) — philosophy of science, the Greek inheritance