The Standard Model. What a dull name for the most accurate scientific theory known to human beings.
More than a quarter of the Nobel Prizes in physics of the last century are direct inputs to or direct results of the Standard Model. Yet its name suggests that if you can afford a few extra dollars a month you should buy the upgrade. As a theoretical physicist, I’d prefer The Absolutely Amazing Theory of Almost Everything. That’s what the Standard Model really is.
Many recall the excitement among scientists and media over the 2012 discovery of the Higgs boson. But that much-ballyhooed event didn’t come out of the blue — it capped a five-decade undefeated streak for the Standard Model. Every fundamental force but gravity is included in it. In short, the Standard Model answers this question: What is everything made of, and how does it hold together?
You know, of course, that the world around us is made of molecules, and molecules are made of atoms. Chemist Dmitri Mendeleev figured out in the 1860s how to organize all atoms — that is, the elements — into the periodic table that you probably studied in middle school.
Physicists like things simple. We want to boil things down to their essence, a few basic building blocks. By 1932, scientists knew that all those atoms are made of just three particles — neutrons, protons and electrons.
That would have been a satisfying place to stop. Just three particles. Three is even simpler than five. But held together how? The negatively charged electrons and positively charged protons are bound together by electromagnetism. But the protons are all huddled together in the nucleus and their positive charges should be pushing them powerfully apart. The neutral neutrons can’t help. What binds these protons and neutrons together?
Meanwhile, nature cruelly declined to keep its zoo of particles to just three. Really four, because we should count the photon, the particle of light that Einstein described. Four grew to five when Anderson measured electrons with positive charge — positrons — striking the Earth from outer space. Five became six when the pion, which Yukawa predicted would hold the nucleus together, was found. Then came the muon. By the 1960s there were hundreds of “fundamental” particles.
Into this breach sidled the Standard Model. It was not an overnight flash of brilliance. Instead, there was a series of crucial insights by a few key individuals in the mid-1960s that transformed this quagmire into a simple theory, and then five decades of experimental verification and theoretical elaboration: Quarks. All the material of our daily lives is made of just up and down quarks and anti-quarks and electrons.
Discovering the Higgs boson in 2012, long predicted by the Standard Model and long sought after, was a thrill but not a surprise. It was yet another crucial victory for the Standard Model over the dark forces that particle physicists have repeatedly warned loomed over the horizon. Concerned that the Standard Model didn’t adequately embody their expectations, physicists have made numerous proposals for theories beyond the Standard Model. These bear exciting names like Grand Unified Theories, Supersymmetry, Technicolor and String Theory.
Sadly, at least for their proponents, beyond-the-Standard-Model theories have not yet successfully predicted any new experimental phenomenon or any experimental discrepancy with the Standard Model.
After five decades, far from requiring an upgrade, the Standard Model is worthy of celebration as the Absolutely Amazing Theory of Almost Everything.