Uncertainty principle
We owe to the great German physicist Werner Heisenberg (1901-1976) in 1927 to have formulate the uncertainty principle of quantum physics. He was only 26 years! This principle describes how a particle can change its nature in a very short time during which its energy can not be definite with precision. In the case of a down quark transformation into an up quark with a W boson, the uncertainty principle makes it possible to quantify this time to 10-26 s. Normally the W boson is reabsorbed by the quark which becomes again "down". However during this extraordinarily short time, there is a very small probability for the W boson to decay into an electron and an antineutrino. This is the origin of beta radioactivity.
IN2P3