The idea that all matter is constituted of small particles (atoms) was first proposed by DemocritusDemocritus (c. 460–c. 370 BC), a Greek thinker. This hypothesis was given a scientific justification much later, as the English researcher John DaltonDalton, John (1766–1844) studied the proportion of the elements required to form a compound, e.g., the volumes of hydrogen and oxygen, to form water (H2O). Only in the twentieth century did the New Zealander Ernest Rutherford (1871–1937) determine that atoms have a tiny nucleus, around which the electrons turn. The Danish physicist Niels BohrBohr, Niels (1885–1962) proposed the first model that describes the atoms. The German Max PlanckPlanck, Max (1858–1947) suggested that atoms absorbed and irradiated energy in packets, or “quanta.quanta” The German-American Albert EinsteinEinstein, Albert (1879–1955) later advanced the idea that light and radio waves carried discrete packets of energy, or quanta. The ideas of PlanckPlanck, Max, EinsteinEinstein, Albert, and others defined a new physics, subsequently to be known as quantum mechanicsQuantum Mechanics. In this conception, all matter—including the particles—presents wavelike properties. One of the triumphs of this new theory is that it explained the origin of magnetism, which rests on a quantum interaction (“exchange”) between electrons.