A particle can pass through a wall of energy it shouldn't have the strength to climb

In classical physics, a particle without enough energy to clear a barrier simply bounces back. In 1928, George Gamow showed that quantum particles can instead 'tunnel' straight through an energy barrier they could never climb over, explaining why unstable atomic nuclei randomly emit alpha particles at all. The same tunnelling effect later turned out to power nuclear fusion in stars and makes technologies like the scanning tunnelling microscope and flash memory possible.

— George Gamow, Zur Quantentheorie des Atomkernes — Zeitschrift für Physik, 1928