Erwin Schrödinger

The teaching

Taught from his own papers and books, above all the papers of 1926 and 1935, What Is Life? (1944) and My View of the World.

The wave equation

Schrödinger's papers of 1926 describe the electron in an atom not as a point in an orbit but as a wave, and the stable states of the atom as the standing patterns that wave can form. A violin string held at both ends can vibrate only in certain ways, its fundamental and its harmonics, and the whole numbers that count them come from the string itself. In the same way the allowed energies of the atom are the proper values of his equation, and the whole numbers of quantum theory arise, as he wrote, as naturally as the number of nodes of a vibrating string, with no rule laid on from outside. The wave function the equation governs became the working tool of the physics of atoms, molecules and solids.

The cat and the entangled pair

In 1935 he set out a case he called ridiculous. A cat is shut in a steel chamber with a tiny amount of radioactive substance, a counter, a hammer and a flask of poison, so arranged that if one atom decays within the hour the counter fires, the hammer breaks the flask and the cat dies, and the chance of that is even. If the quantum description were taken as a picture of reality, the state of the whole chamber after the hour would hold the living and the dead cat smeared out in equal parts. His point was that such a blurred model cannot simply be accepted as a picture of the world: the theory needs a clearer account of what its description means.

In the same year he named the feature that makes such cases possible. When two systems have interacted and separated, the best possible knowledge of the whole does not include the best possible knowledge of its parts; their descriptions are entangled, and he called this not one but the characteristic trait of quantum mechanics.

Order from order

What Is Life? asks how a living thing, made of atoms, keeps its order while the rest of nature runs down toward disorder. The laws of physics and chemistry, he explains, are statistical, true for the great numbers of atoms in ordinary things, which is why an organism must be large compared with an atom; this is order from disorder. But heredity rests on very few atoms, the gene, and keeps its pattern unchanged through generations, so it must work by a different principle, order from order, the stability of a molecule held by quantum forces.

He pictured the gene as an aperiodic crystal: not a repeating lattice like salt, but a solid whose atoms are arranged in a sequence that varies, carrying in a small space what he called a code-script, the whole pattern of the individual's future development. Mutations are quantum jumps in that molecule. A living body avoids decay by drawing order from its surroundings, feeding, as he put it, on negative entropy.

The one mind

His philosophy, that consciousness is never found in the plural, that the many minds are one, and that science leaves the knowing subject out of its picture of the world, is taught in the branch The physicists who read the mystics of Physics and the mystics. He held it beside his physics as a view of his own, taken from the Upanishads and from Schopenhauer.

My View of the World gives it the form of a meditation. Sit, he writes in effect, before mountains and fields, and consider that this knowing, feeling and choosing that you call your own cannot have sprung from nothing a few years ago; it is, in the conviction of the Vedanta, eternal and numerically one in all who feel. Then you may lie on the ground, stretched out on the earth, certain that you are one with her and she with you, and as firmly established as she. The Brahmins, he writes, put it in a formula at once mystic and simple: tat tvam asi, this is you.