This article is part of a special series celebrating the 100th anniversary of the birth of quantum theory. Read more here
The seeds of quantum theory were sown by Albert Einstein and others as early as 1905. But the theory came together properly 100 years ago in 1925 – and has exerted its influence ever since, as this timeline shows.
> 1905 Riffing on earlier work by Max Planck, Albert Einstein suggests that light is made of particles with certain energies. These “quanta of light” were an early step on the road to quantum theory.
> 1913 Niels Bohr produces a quantum description of the atom in which electrons can only exist in certain orbits with fixed energies.
> 1919 Physicist Hendrika Johanna van Leeuwen writes a thesis proposing that magnetism is also a quantum mechanical phenomenon.
> 1925 On the windswept island of Helgoland, Werner Heisenberg carries out a calculation that treats the electron’s characteristics not as single values, but as tables of values. In this, his supervisor, Max Born, spots a key truth of quantum mechanics (see “Carlo Rovelli on what we get wrong about the origins of quantum theory”).
> 1926 Erwin Schrödinger develops an alternative quantum framework that paints electrons as waves using a mathematical construct called the wave function.
> 1935 Schrödinger devises a thought experiment in which a cat in a closed box may be considered both alive and dead while it is unobserved. Einstein, Nathan Rosen and Boris Podolsky write a paper on quantum entanglement, which links two particles even when separated by…
