Glossary · History Quantum tunneling refers to the quantum
mechanical phenomenon where a particle tunnels through a barrier
that it classically could not surmount. This plays an essential
role in several physical phenomena, such as the nuclear fusion
that occurs in main sequence stars like the sun. It has
important applications to modern devices such as the tunnel
diode and the scanning tunneling microscope. The effect was
predicted in the early 20th century and its acceptance, as a
general physical phenomenon, came mid-century. Tunneling is
often explained using the Heisenberg uncertainty principle and
the wave–particle duality of matter. Purely quantum mechanical
concepts are central to the phenomenon, so quantum tunnelling is
one of the novel implications of quantum mechanics. Quantum
tunneling was developed from the study of radioactivity, which
was discovered in 1896 by Henri Becquerel. Radioactivity was
examined further by Marie and Pierre Curie, for which they
earned the Nobel Prize in Physics in 1903.