Today, the universe as we know it is governed by four fundamental forces: the strong nuclear force, the weak nuclear force, electromagnetism, and gravity. However, these four forces aren’t exactly as distinct as you think. Electromagnetism and the weak nuclear force, for example, were once the same force—the electroweak interaction.

This force only existed in the early days of the universe—or, should we say, early trillionths of a second of the universe—before the Higgs mechanism (also known fantastically as the Mexican hat mechanism, due to its shape) separated the two forces and applied mass to the Z and W bosons. Those bosons, in turn, carry the weak nuclear force, which is the thing responsible for radioactive decay. The electroweak force only existed at temperatures approaching 1015 Kelvin (about 1,800,000,000,000,000 ºF), which is why you’re not seeing much electroweak action nowadays.