First of all, The Standard Model isn’t a very good name and doesn’t do justice for the grandeur and significance of this theory. The Standard Model is one of the most accurate scientific theories known to humanity up to this point. More than one-quarter of the Nobel Prizes in Physics awarded in the last century have either been a direct input to or a result of the Standard Model. If you’re scientifically inclined, you might remember the grandiosity and pomp surrounding the discovery of the Higgs Boson in 2012. However, that much ballyhoo didn’t just emerge out of the blue, but was instead built on the backbone of the Standard Model. The Standard Model has thus far been able to explain everything in physics except gravity (but scientists are still working on it feverishly!). Now, let’s dive into a deeper understanding of this theory, which seems to be the theory of everything (except gravity).
We’re all aware that the world around us is made of molecules and the molecules are primarily made of atoms. The chemist Dmitri Mendeleev, in the 1860s, figured out a way to arrange all the known atoms of the time into what are known as elements in the periodic table. This is the dreaded periodic table (at least for some of us) that we learned about in middle school. There are 118 elements present on the periodic table. Now, physicists being physicists, they like to make things simple. They like stripping things down to their bare essence—to the building blocks. The ancients believed that there were only five elements, but we’ve come a long way from 5 to 118.
Now, if you though the periodic nightmare ended in school, I’m sorry to say it just got a bit bigger. By 1932, scientists knew that atoms were made of three fundamental particles—protons, neutrons and electrons. The protons and neutrons are bound together to form the nucleus, while the electrons are thousands of times lighter than the protons/neutrons, and whirl around the nucleus at a rate close to the speed of light. Calculations show that the momentum of electrons is about 2200 kilometers per second. To put that in perspective, it’s just 1% less than the speed of light.
Now, the famous physicists of the time, such as Max Planck, Niels Bohr, Erwin Schrodinger and Werner Heisenberg, went on to create a new branch of physics known as quantum mechanics to explain this motion. It would be highly satisfying for an ordinary mind to stop here, as this seems to present a fruitful understanding of the fundamental building block of the Universe. However, for the more scientifically inclined, another fundamental question arises. How exactly are these particles held together? The particles in this instance are the protons, neutrons and electrons. It’s known that the negatively charged electrons and the positively charged protons are attracted to one another due to electromagnetism. But how are the protons huddled together in the nucleus and how do they not repel one another (proton to proton) with great force? Basically, how are the protons and neutrons held together?
Zoo of Particles
Given how curious the human mind can be, and how diligent the researchers were in this field, the three fundamental particles grew to become four. The fourth is the photon, the particle of light described by Einstein. Four grew to five when another anomalous particle was found. The reason for its anomalous nature was that (believe it or not) it appeared to be an electron discovered to be emitting a positive charge. This particle ended up being known as the positron. This particle was found by Carl D. Anderson, who was of Swedish descent but spent the bulk of his life in the United States of America. Then came the discovery of the pion, discovered by Yukawa, which made five into six.
Further investigation led to the establishment that the pion was the reason for the binding of the nucleus. Then came the muon, which was 200 times heavier than electrons, but it is considered to be the “twin” of the electron. That brings the total number of discussed particles up to this point to seven.
By now, you’re probably used to the fact there is no conclusive end to something when it comes to science. By the 1960s, hundreds of fundamental particles had been discovered. In conjunction with the well-organized periodic table came the long list of baryons, leptons and mesons. Baryons constitute the heavier elements, like the protons and neutrons, while leptons consisted of the lighter particles, such as electrons and neutrinos. Mesons consisted of particles like the pions. Into this breach sidled the Standard Model. It was not a flash of brilliance, but rather, there there was a series of crucial insights by a few key individuals in the mid-1960s that transformed this quagmire into a simple theory, followed by five decades of experimental verification and theoretical elaboration!