Standard model. What a stupid name for the most accurate scientific theory known to mankind. More than a quarter of the Nobel Prizes in physics of the last century were awarded to works that were either directly or indirectly related to the Standard Model. Her name, of course, is such as if you can buy an improvement for a couple of hundred rubles. Any theoretical physicist would prefer the “amazing theory of almost everything,” which it really is.
Many remember the excitement among scientists and in the media over the discovery of the Higgs boson in 2012. But its discovery did not come as a surprise and did not come out of nowhere - it marked the 50th anniversary of the winning streak of the Standard Model. It includes every fundamental force except gravity. Any attempt to refute it and demonstrate in the laboratory that it needed to be completely reworked - and there were many - failed.
In short, the Standard Model answers this question: what is everything made of and how does everything fit together?
The smallest building blocks
Physicists love simple things. They want to shatter everything to its core, to find the most basic building blocks. It is not so easy to do this in the presence of hundreds of chemical elements. Our ancestors believed that everything consists of five elements - earth, water, fire, air and ether. Five is much simpler than one hundred and eighteen. And also wrong. You certainly know that the world around us is made of molecules, and molecules are made of atoms. Chemist Dmitry Mendeleev figured this out in the 1860s and presented atoms in the table of elements, which is studied in school today. But there are 118 of these chemical elements. Antimony, arsenic, aluminum, selenium … and 114 more.
In 1932, scientists knew that all these atoms are made up of only three particles - neutrons, protons and electrons. Neutrons and protons are closely related to each other in the nucleus. Electrons, thousands of times lighter than them, circle around the nucleus at a speed close to light. Physicists Planck, Bohr, Schrödinger, Heisenberg, and others have introduced a new science - quantum mechanics - to explain this movement.
It would be great to stop there. Only three particles. It's even easier than five. But how do they stick together? Negatively charged electrons and positively charged protons are held together by the forces of electromagnetism. But the protons are bouncing in the nucleus and their positive charges should push them away. Even neutral neutrons won't help.
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What binds these protons and neutrons together? "Divine Intervention"? But even a divine being would have trouble keeping track of each of the 1080 protons and neutrons in the universe, holding them by willpower.
Expanding the zoo of particles
Meanwhile, nature desperately refuses to store only three particles in its zoo. Even four, because we need to account for the photon, the particle of light described by Einstein. Four turned into five when Anderson measured positively charged electrons - positrons - that hit the Earth from outer space. Five became six when the peony holding the core as a whole and predicted by Yukawa was discovered.
Then the muon appeared - 200 times heavier than the electron, but otherwise its twin. It's already seven. Not so easy.
By the 1960s, there were hundreds of "fundamental" particles. Instead of a well-organized periodic table, there were only long lists of baryons (heavy particles like protons and neutrons), mesons (like Yukawa pions) and leptons (light particles like electrons and elusive neutrinos), without any organization or principles of design.
And in this abyss the Standard Model was born. There was no insight. Archimedes didn't jump out of the bathroom shouting "Eureka!" No, instead, in the mid-1960s, a few smart people made important assumptions that turned this quagmire, first into a simple theory, and then into fifty years of experimental testing and theoretical development.
Quarks. They got six options that we call flavors. Like flowers, just not so tasty smelling. Instead of roses, lilies and lavender, we got up and down, strange and enchanting, lovely and true quarks. In 1964, Gell-Mann and Zweig taught us how to mix three quarks to make a baryon. A proton is two up and one down quark; neutron - two lower and one upper. Take one quark and one antiquark - get a meson. A peony is an up or down quark associated with an up or down antiquark. All matter with which we are dealing consists of up and down quarks, antiquarks and electrons.
Simplicity. Not exactly simplicity though, because keeping quarks bound isn't easy. They bond together so tightly that you will never find a quark or antiquark wandering on its own. The theory of this connection and the particles that take part in it, namely gluons, are called quantum chromodynamics. This is an important part of the Standard Model, mathematically complex, and in some places even unsolvable for basic mathematics. Physicists do their best to make calculations, but sometimes the mathematical apparatus is not sufficiently developed.
Another aspect of the Standard Model is the "lepton model". This is the title of a landmark 1967 paper by Steven Weinberg that combined quantum mechanics with essential knowledge of how particles interact and organize them into a unified theory. He turned on electromagnetism, associated it with a "weak force" that leads to certain radioactive decays, and explained that these are different manifestations of the same force. The Higgs mechanism was included in this model, giving mass to fundamental particles.
Since then, the Standard Model has predicted the results of experiments after results, including the discovery of several varieties of quarks and W and Z bosons - heavy particles that, in weak interactions, fulfill the same role as a photon in electromagnetism. The possibility that neutrinos have mass was missed in the 1960s, but confirmed by the Standard Model in the 1990s, several decades later.
The discovery of the Higgs boson in 2012, long predicted by the Standard Model and long awaited, did not come as a surprise, however. But it was another major victory for the Standard Model over the dark forces that particle physicists regularly expect on the horizon. Physicists do not like that the Standard Model does not correspond to their ideas about the simple, they are worried about its mathematical inconsistency, and they are also looking for ways to include gravity in the equation. Obviously, this translates into different theories of physics, which may be after the Standard Model. This is how grand unification theories, supersymmetry, technocolor, and string theory emerged.
Unfortunately, theories outside the Standard Model have not found successful experimental evidence and no major flaws in the Standard Model. Fifty years later, it is the Standard Model that comes closest to being a theory of everything. Amazing theory of almost everything.
Ilya Khel