What Was It Like When The Higgs Gave Mass To The Universe?
“Without this critical gauge symmetry associated with electroweak symmetry breaking, existence wouldn’t be possible, as we do not have stable, bound states made purely of massless particles. But with fundamental masses to the quarks and charged leptons, the Universe can now do something it’s never done before. It can cool and create bound states like protons and neutrons. It can cool further and create atomic nuclei and, eventually, neutral atoms. And when enough time goes by, it can give rise to stars, galaxies, planets, and human beings. Without the Higgs to give mass to the Universe, none of this would be possible. The Higgs, despite the fact that it took 50 years to discover, has been making the Universe possible for 13.8 billion years.”
It’s puzzling to think about, but the particles that make up everything we know of and interact with in the Universe, like the quarks and leptons that make up the atoms that make us up, were once all completely massless. Just like the photon, the massless quantum particle that creates light, moves at the speed of light today and cannot exist in a bound state, the up-and-down quarks that make up protons and neutrons, as well as the electron that makes chemistry possible, were all massless in the early days of the Universe. What changed? A fundamental symmetry, the electroweak symmetry, broke as the Universe cooled below a certain threshold. When that happened, the Higgs boson as we know it today came into existence, and 15 other particle that coupled to it all obtained non-zero rest masses.