Bohr’s Quantum: 1926–

“How wonderful that we have met with a paradox. Now we have some hope of making progress,” said Niels Bohr with characteristic irony. The quantum view of the atom began with Bohr. Coming from Denmark, he worked with Rutherford, who although famously skeptical about theoreticians, supported him. Max Planck had previously introduced the idea of the quantum, and Einstein had extended it from matter to light, but Bohr’s proposal that electrons can adjust their orbits only by quantum leaps was revolutionary. The next revolution was Schrödinger’s description of electrons as waves instead of particles. This led to recognition of the wave–particle duality. The rest of the 20th century was marked by the realization that the apparently fundamental particles of the nucleus, the proton and the neutron, each actually consisted of a series of sub-particles. The wave–particle duality created a baffling series of paradoxes. Following revolutions tended to be driven by theoreticians, and massive team efforts were required to identify the sub-particles experimentally.