Elementary particle physics is a specialized field filled with strange jargon and seemingly incomprehensible mathematics. Its caretakers are a group of mostly low-key academics save for a handful, such as Richard Feynman and Steven Hawking, who have somewhat become cult figures.
One of those low-key academics who is relatively unknown outside the realm of theoretical physics is Dr. Peter Higgs, an English theoretical physicist who, just a little over forty years ago, published a theory that helped physicists to better understand the fundamental interactions of subatomic particles. This year, with the start-up of the gigantic Large Hadron Collider at the Cern Laboratory, Dr. Higgs hopes to finally see the heart of his theory observed in nature.
The world of the atom is very strange and very different from the world in which we live. For over a century, physicists have been trying to understand how it works, and they have come up with some comprehensive theories that are complicated, but surprisingly accurate.
According to the Standard Model, the fundamental laws that govern natural phenomena (light, sound, gravity, heat, electricty, chemical reactions, etc.) can be derived from four fundamental interactions that take place at the sub-atomic level. These interactions are: 1) electromagnetic interactions (familiar to us as electricity and magnetic fields), 2) strong interactions (which hold protons and neutrons together within the nucleus of the atom), 3) weak interactions (familiar to us as radioactivity), and 4) gravitational interactions.
Theoretical physicists have worked for decades to develop a comprehensive understanding of how these interactions work, and how they are related one to another. Their ultimate goal is to develop a single "Grand Unified Theory" that can be used to eloquently explain each of the four fundamental interactions. The first successful elementary particle theory was quantum electrodynamics, which explained electricity and magnetism at the subatomic level. Then, physicists took the first step toward the GUT by creating a theory that unified the electromagnetic and weak interactions into one "electroweak" interaction. Further refinement led to the development of the Standard Model, which unified the electroweak interaction with the strong interaction. The only fundamental interaction that is not well understood is gravitation, but theoretical physicists have been working on a theory of quantum gravitation for some time now.
The Standard Model explains electroweak and strong interactions in terms of particles. These particles are not like hard grains of sand or poppy seeds; rather, they are fields of energy condensed around a point in space. These fundamental particles fall into two classes: bosons (named after Satyendra Nath Bose) and fermions (named after Enrico Fermi). The classifications of fermions is complicated -- there are 12 varieties of fermions in the quark family (including particles and antiparticles) and 12 varieties of fermions in the lepton family (including particles and antiparticles).
Despite the confusing array of particles developed by the Standard Model, the basic explanation of natural phenomena derived from the SM is quite simple. According to the SM, all matter is made up of atoms, and all atoms are made up of protons, neutrons, and electrons. Protons, neutrons, and electrons are themselves made up of fermions -- protons and neutrons are made up of quarks, while the electron is the most stable member of the lepton family.
So, when we say that atoms react with one another, what we are really describing is the aggregation of a staggering number of sub-atomic reactions between quarks and leptons. The basic reaction mechanism is:
Two fermions (quarks or leptons in their original state) interact ---> a boson exchange occurs ---> two fermions (quarks or leptons in an altered state) emerge
Wikipedia notes, "The exchange of bosons always carries energy and momentum between the fermions, thereby changing their directions of flight and their respective speed. It may transport a charge between the fermions, changing the charges of the fermions in the process (e.g. turn them from one type of fermion to another type of fermion)."
As an example, here is how the Standard Model explains the force created by a magnetic field. According to the SM, magnetic fields are the result of interactions between electrons -- remember, electricity and magnetism are two manifestations of the same fundamental interaction; you can make a magnet using an electric current (an electromagnet), likewise you can generate electricity by moving a magnet through a coil of wire. The SM states that as one electron (a fermion) interacts with another electron, it emits a virtual photon (a boson) which is absorbed by another electron. As the first electron emits the photon, it recoils backwards, while the second electron is propelled forward as it absorbs the photon. Thus, a force is created between the electrons. On a macro scale, as countless billions upon billions of electrons repel one another, this force is observed as a magnetic field.
Physicist Richard Feynman created a system of simple diagrams to illustrate these interactions. Here is what the electromagnetic repulsion between two electrons looks like in an animated Feynman diagram:
So far so good. But when the SM is applied to more complex phenomena, the calculations become very difficult. This enormous mathematical complexity stems from the rigid requirements placed on the theory; namely that it must obey the laws of quantum mechanics and special and general relativity, and that it must obey the well-known principles of energy conservation, invariance, and symmetry (with only a handful of specific exceptions). This is just a fancy way of saying that the theory must be valid for every variation of time, space, and energy that is known to have existed in the universe. Once you account for all of those things, you have one heck of a mess.
But because the SM works, physicists and cosmologists have been able to input the theoretical conditions that existed in the very early universe, just milliseconds after the Big Bang (when the entire mass of the universe was rapidly expanding outward from a single point of origin containing an incredible amount of energy) and subsequently predict the types of elementary particles that should have existed during the first three minutes of the life of our universe.
But how can we verify these predictions? This is where the job of the experimental physicist becomes very tricky. While the structures made of fermions (protons, neutrons, electrons, and so on) are stable enough to form physical matter, observing the actual quarks and leptons (other than the electron) is difficult, because it takes enormous amounts of energy in order to break down the subatomic particles held together by strong interactions. And observing the bosons (other than the photon, which we perceive as light) is even harder, because these virtual particles exist only during fermion interactions, and their lifespan is on the order of 3x10-27 seconds, or 0.000000000000000000000000003 seconds.
In order to observe these elementary particles, physicists have built enormous machines called particle colliders. These machines accelerate atoms to nearly the speed of light, and then collide them. Scientists then observe the particles that briefly appear during the interactions of the atoms as they collide. So far, experimental physicists have found a considerable number of the unusual sub-atomic particles predicted by the Standard Model, so confidence in the Standard Model (even though it does not account for gravitation) is very high.
Which brings us back to Peter Higgs. In 1964, Dr. Higgs published groundbreaking theoretical work on the weak interaction. The so called "Higgs mechanism" is crucial to the electroweak theory. It postulates a hypothetical "Higgs field" that permeates all of space, and uses a hypothetical "Higgs boson" as the carrier of the field, which in turn gives mass to the W and Z bosons. Wikipedia notes, "The Higgs mechanism is the only way an elementary vector particle, like the W or the Z can have a mass. Interactions with the associated Higgs boson gives mass to the quarks and leptons in the standard model." And because quarks and leptons (and, consequently, protons and neutrons and atoms) have mass, they form the basic building blocks of matter. Thus, if the electroweak theory of the Standard Model is correct (and physicists are very confident that it is), then the Higgs boson must exist.
Yet the mass of the Higgs boson cannot be derived from the Standard Model. Experimental physicists have attempted to calculate a lower limit for the Higgs boson mass based on the observed mass of other subatomic particles, but so far nothing resembling a Higgs boson has been observed.
Dr. Higgs is now 78 years old, and he hopes that the Large Hadron Collider, which can theoretically produce energy levels within the range of the predicted lower limit for the Higgs boson's mass, will finally show the world an elusive Higgs boson, a particle that exists at extreme energy levels that occurred in nature only during the moments immediately following the Big Bang.
The Higgs boson has been given the colloquial moniker "The God Particle," so called because of the God-like omnipresence of the theoretical Higgs field, and its fundamental necessity to the existence of atoms, and therefore to the existence of nature itself.
Discovering (or failing to discover) the Higgs boson will certainly increase our meager knowledge of how the universe works. "I will certainly open a bottle of something," said Dr. Higgs, in the event that his namesake particle is discovered. But if its discovery eludes scientists, Dr. Higgs will be "very, very puzzled. If it’s not there, I no longer understand what I think I understand."
What a curious way to spend one's final years.