Today, all the way down. The University of Houston presents this series about the machines that make our civilization run, and the people whose ingenuity created them.

By the early 1960s particle physics was in a bit of a mess. The basic components of the atom were well established - the proton, neutron, and electron. Together, they formed the day-to-day world we interacted with. It seemed only fitting that these particles should be the end of the story. But they weren't.

Carbon
  Photo Credit: Pixabay

The problem was that physicists kept discovering more and more particles. Some were smaller than protons and neutrons but larger than electrons. Properties like electric charge didn't add up. At first the particles were discovered in nature, the result of cosmic rays crashing to earth from outer space. But soon physicists were creating their own new particles by hurling high-energy streams of electrons and protons crashing into waiting targets. The particle accelerators that achieved these feats earned the nickname atom smashers. Hundreds of new particles were discovered, all of which were new and different. Physicists at the time joked that they could just as well have been botanists, since their job had become one of discovery and record keeping. Where was the science? And more importantly, why were there so many seemingly haphazard particles? The subatomic world had become, in the physicists' own words, a particle zoo.

As the zoo kept expanding, it seemed there must be something more elementary - some smaller particles from which all the others were put together. And by the early sixties the ideas were beginning to congeal. Through an amazing sequence of creative guesswork, theorizing, and experimentation, a new model of the subatomic world emerged: the standard model of particle physics.

Standard Model of Elementary Particles
  Photo Credit: Wikipedia

The standard model has seventeen particles not counting antiparticles. The electron remains an elementary particle, but not the proton or neutron. They're made up of three quarks, which are held together with gluons. Quarks come in six flavors. These flavors have the names up, down, charm, strange, top, and bottom. Every flavor of quark takes one of three colors: red, blue, or green. Beyond quarks there are leptons and bosons. If these particles prove anything, it's that particle physicists have a good sense of humor - doubly so when we realize these whimsical names represent the most fundamental building blocks of the universe.

Inside a proton: two up quarks and one down quark, all of different colors
  Photo Credit: Wikimedia

But do they really? Are these really the indivisible particles hypothesized since the time of the ancient Greeks? The standard model is remarkable, yet it lacks the elegance of the periodic table of atomic elements. Could it be that even more elementary particles underlie those found in the standard model? Could quarks be made of quincies? Bosons of newsons? Well, yes. It's not a commonly held belief. And there's still plenty of work to do when it comes to the standard model as it now stands. But then, who knows? The world of subatomic particles is already so strange that it's mystifying. Will we ever find we've reached all the way down?

I'm Andy Boyd at the University of Houston, where we're interested in the way inventive minds work.

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String theory posits the existence of building blocks that are even smaller than those found in the standard model of particle physics. However, no particular manifestation of string theory is widely accepted, and the hypothesized strings are so small as to be beyond experimental verification at this point in time.

Particle Zoo. From the Wikipedia website: https://en.wikipedia.org/wiki/Particle_zoo. Accessed December 4, 2018.

Standard Model. From the Wikipedia website: https://en.wikipedia.org/wiki/Standard_Model. Accessed December 4, 2018.

Martinus Veltman. Facts and Mysteries in Elementary Particle Physics. Singapore: World Scientific Publishing, 2018.