Planck's quantum hypothesis of 1900 and Bohr's atomic model of 1913 were rules bolted onto classical physics: they worked, but nobody knew why. In 1925 Werner Heisenberg proposed abandoning unobservable orbits altogether and writing only relations between measurable quantities; Max Born and Pascual Jordan showed that the scheme was matrix algebra. A year later Erwin Schrödinger published a wave equation that gave the same results, and the two formulations were soon shown to be mathematically equivalent.

Interpretation proved harder than the equations. Born argued that it is not the wave function but its square that is a probability density: the theory says not where a particle is but how likely it is to be found there. In 1927 Heisenberg showed that position and momentum cannot both be known to arbitrary precision — the uncertainty arises from the structure of the theory, not the crudeness of instruments. That October the physicists gathered at the Fifth Solvay Conference argued it out; Einstein's objections to Bohr, and the line about God not playing dice, come from that exchange.

While the philosophical argument continued, the theory became the ground of technology: semiconductors, the transistor, the laser, MRI, LEDs and quantum computers all follow from this framework. Einstein's objection was not sterile either — the EPR paper of 1935 turned, thirty years later, into an experimental question through Bell's inequalities, and the 2022 Nobel Prize in Physics went to three physicists who carried out those experiments.