How to make gold

Gold is a rare and special element, intimately connected to the history of civilisation. It is found in meteorites, in the Earth's crust, in the oceans, in all living things and in the Sun, which is estimated to contain about 1018 tonnes of gold. This paper reviews the physics of gold at a non-technical level. It shows how all aspects of gold, from its colour to its creation, can only be described by Einsteinian physics. Quantum physics, which began with Einstein's prediction of photons in 1905, combined with his theory of relativity, explains gold's golden hue. The quantum physics of radioactive decay allows gold isotopes to be used in medicine. The first step towards understanding how gold is created in the universe was the prediction and discovery of neutron stars. Next were observations that proved that gold was not created in supernova explosions where neutron stars were born. These unsuccessful attempts to explain how gold is created led to a new theory that coalescence of pairs of neutron stars, driven by gravitational waves according to Einstein's 1916 prediction, was the true source of gold. In 2017, this prediction was proved in dramatic observations by gravitational wave detectors, combined with gamma ray observatories and optical telescopes. Events such as this one, but occurring more than 5 billion years ago, are now thought to be the source of gold in the Solar System.