Category: The Fundamental Particles

A feature common to all of the quantum field theories is that the exchange particles are all bosons, not fermions. This is actually required by the same properties of spin that led us to the Pauli exclusion principle in the first place. All of the known exchange bosons have spin quantum number equal to one.…

The weak interaction has been theoretically united with the electromagnetic force, a major victory for physics that occurred rather recently. It was in the 1960s that Glashow, Salam, and Weinberg came up with their unification scheme based on QED. Initially, their work predicted that there should be a total of four massless bosons to mediate…

The next logical step for the intrepid theoretical physicist is to bring the fourth and last fundamental interaction, gravity, under the same sort of quantum field umbrella as the other forces. Unfortunately, we have no real successes to report in this effort. There are a lot of reasons for this, but here we will describe…

Bolstered by the successes of using quantum field theory to describe electrodynamics and the weak interaction, theorists immediately tried to come up with a quantum field theory for the strong nuclear force. Unfortunately, however, the sailing wasn’t quite as smooth this time around. We originally named the strong force “strong” because it had to overcome…

The weak interaction is easily treated with the same sort of quantum field theory as we just described for electromagnetism. There are some important differences, however. The big one is that the exchanged particle is not a photon, but one of a set of three particles, called the Z0, W+, and W–. Like the photon, these three particles…

Quantum electrodynamics is the name of the quantum field theory that applies to the electromagnetic interaction. As with classical electrodynamics, it only applies to charged particles like protons and electrons. In QED the interaction between, say, two electrons is modeled as the exchange of a fruitcake-like boson—in this case the “virtual” photon (ɣ). We saw…

After the quantum revolution of the 1920s and 1930s, theoretical physicists developed a powerful way to deal with interactions that is consistent with all the requirements of quantum physics we have outlined so far. This approach essentially “quantizes” the force fields that were inherited from classical physics. It makes explicit use of the basic symmetries…

These four particles and four antiparticles are enough to describe just about everything we encounter in our daily lives. But, they are not enough to build all of the other particles that physicists have observed in the laboratory (e.g., during high-energy particle collisions). Soon after particle accelerators reached the energy equivalent to the mass of…

As it turns out, all of the most fundamental particles that eventually make up ordinary matter are fermions, with spin quantum number equal to 1⁄2. These include the familiar electron (e), along with two flavors of quarks that join to form protons and neutrons. These two kinds of quarks are called “up” and “down,” for no…

We introduced the ancient Greek concept of atomos, a sort of tiny and indivisible particle from which the universe is made. Though this idea was seriously rekindled in the early nineteenth century, it didn’t take long to show that the particles then believed to be fundamental were actually made up of smaller things. But did this…