: Gabriela Secara, Perimeter Institute)

It was 13.8 billion years ago that our Universe, as we know it, began: at the start of the hot Big Bang. After , the Universe became filled , all while it remained expanding at a very rapid rate. Almost immediately, the Universe began cooling as it expanded, and the temperatures dropped precipitously. After only a trillionth of a second, things had cooled enough that the electroweak symmetry broke, creating four fundamental forces and allowing the Higgs to give rest mass to the Standard Model particles. In the aftermath of that:

• an early quark-gluon plasma condensed into individual baryons, such as protons and neutrons,
• the remaining antimatter annihilated away, leaving only a tiny amount of leftover normal matter,
• the weak interactions froze out, creating a background of cosmic neutrinos and antineutrinos,
• about 20% of the neutrons that existed decayed into…