1915

Nobel Prize in Physics

William Bragg · Lawrence Bragg

William and Lawrence Bragg — father and son — worked out how to use X-ray diffraction to determine the positions of atoms inside crystals. Lawrence derived the key equation at the age of twenty-two; William built much of the apparatus. They remain the only parent-child pair to share a Nobel Prize.

Nobel Prize in Chemistry

Richard Willstätter

Willstätter determined the structure of chlorophyll: a porphyrin ring with a magnesium atom sitting at its centre, coordinated by nitrogen atoms. It was the molecule responsible for almost all plant growth on Earth, and no one had previously known what it looked like.

Nobel Prize in Literature

Romain Rolland

Rolland was a pacifist who spent the war years in Geneva writing against it and was widely despised in France as a consequence. The prize cited his "lofty idealism" and sympathy for different types of human beings. His ten-volume novel cycle "Jean-Christophe" had been appearing since 1904.

Einstein publishes field equations of general relativity

Between November 4 and November 25, Einstein presented four papers to the Prussian Academy of Sciences in Berlin, culminating in the field equations: ten coupled nonlinear partial differential equations relating the curvature of spacetime to the distribution of mass and energy. Gravity, he proposed, was not a force but a geometry — mass bends the fabric of space, and other masses follow the curves. He checked his equations against the anomalous advance of Mercury's perihelion and found they gave the right answer. He was, by his own account, beside himself with joy.

Sommerfeld extends the Bohr model

Arnold Sommerfeld allowed electron orbits to be elliptical rather than circular, and added relativistic corrections to the energy levels. The result explained the fine structure of spectral lines — the splitting of lines into close-paired doublets — which Bohr's original circles could not account for.

Bragg's law of X-ray diffraction

The equation nλ = 2d sin(θ) — Bragg's law — describes precisely when X-rays reflected from crystal planes reinforce rather than cancel each other. Given the angle and the wavelength, you can calculate the spacing between atomic planes; given the spacings, you can build up the crystal's structure. It is still the first equation taught in any crystallography course.

Willstätter determines chlorophyll structure

Chlorophyll contains a magnesium atom at the centre of a porphyrin ring, with a long hydrocarbon tail that anchors it in the membrane. Willstätter established this by patient chemical degradation, comparing the fragments to known compounds. The fact that the molecule doing all the work of photosynthesis runs on magnesium rather than some rarer element seems, in retrospect, characteristic of the living world's relentless practicality.

Tropomyosin identified in muscle tissue

Tropomyosin was isolated and identified as a protein winding along the actin filaments in muscle, where it regulates contraction by blocking or exposing the sites where myosin binds. The machinery of muscle turned out to be more intricate than anyone had assumed.