The Standard Model
This chart is what is known as the Standard Model. In it shows the elementary particles. These particles cannot be broken down into constituents. These particles are not all of the ones that exist, however. We see our old friend, the electron, but where’s the proton and neutron? Well, we don’t see them, but we see their constituents, quarks. And better yet, those particles are held together by another particle– the gluon. Looking at the model, we see quarks, leptons, and the gauge bosons:
- Quarks: These make up other particles, including the two nucleons, neutrons and protons. Quarks differ in their masses and electric charges and are the only particles to have fractional charges.
- Leptons: There are three main types with three neutrino counterparts, differing in mass and charge. Neutrinos have extremely tiny masses. In fact, billions are passing through your body every second! Electrons are the most familiar leptons.
- Bosons: These particles mediate force. Though photons, W and Z bosons, and gluons have been detected, no one has detected a graviton. Gravitons are theoretical particles which are thought to mediate gravity.
What are the four fundamental forces (FFF)?
Since three of the FFF have a particle mediator, wouldn’t it make sense for gravity to have one? Gravitons are theoretical particles which are thought to mediate gravitational force. Photons mediate the electromagnetic force. Electromagnetism is seen in electricity, magnetism, light, radiation, chemical bonding, friction, and so on. W and Z bosons mediate the weak force which holds together leptons and quarks. It is also responsible for particle transmutation through nuclear decay. Unstable nuclei will spontaneously decay by pushing out particles. It’s worth noting that on a small enough scale (attometers, or 10−18 meters) and with high enough energies, electromagnetism and the weak force are manifestations of the same thing. This is called the electroweak force. Gluons mediate the strong force that holds nuclei together. It is the absolute strongest force there is, as it binds protons of the same charge in the same nucleus. The electromagnetic force would normally repel them, but through the exchange of gluons, the strong force overcomes it.
The Notorious Higgs Boson and the Higgs Field
This is a special kind of boson which is responsible for giving objects their mass* (see below for explanation). Throughout the so-called Higgs Field, some particles interact with it and thus have a mass, whereas those which do not (like photons) have no mass. In other words, particles have no mass until they interact with the Higgs field. The boson itself can be seen as the movement of the interactions of those particles within the field. Fermilab’s Senior Physicist Don Lincoln explains this with a cocktail party analogy.
*The Higgs field gives mass to elementary particles, which is only a tiny fraction of the mass in the universe. Most mass comes from the energy of quarks binding together through gluon exchange. This is called quark-gluon plasma and this is what gives matter most of its mass.
Fermions, Bosons, and the Pauli Exclusion Principle (PEP)
“Fermion” is a name for any particle which obeys the PEP; bosons do not. The PEP, simply put, states that no two particles can exist in the same spot at the same time. Imagine riding a roller coaster: the people riding it are particles, and only two can fit in each seat. You can’t fit into a seat with two people in it since it’s full, so you look for an empty one. This explains fermions, but what about bosons? This is where the analogy fails. The PEP states that two particles with the same spin cannot exist together in the same quantum state. Spin, put simply, is a particle’s intrinsic angular momentum. A quantum state is defined by specific properties and is not a physical location, as the analogy suggests.
For every particle, there is an antiparticle that is exactly the same as the original, except that it has an opposite electrical charge. The only boson with an antiparticle is the W boson, while the others are their own antiparticles. When an antiparticle and a particle collide, they annihilate each other and what’s left over is an immense amount of energy. Sometimes, as with muons and antimuons, other particles are produced. Their masses convert to energy and can be converted back into mass. Remember E = mc2? Mass is just energy moving a lot slower than light.
There are two types of hadrons: baryons and mesons. Baryons are particles made up of 3 quarks (such as nucleons), and mesons are made of one quark and one antiquark.
There is a theory stating that there’s a symmetric particle counterpart to every particle in existence. SUSY could link bosons and fermions together: a boson’s superpartner would be a fermion and a fermion’s superpartner would be boson. This would unify the particles which make up matter (fermions) and the particles which mediate forces (bosons).
Quasiparticles are mathematical models which describe physical phenomena in an easier way. Phonons, for example, are quasiparticles that provide a wonderfully deep and complex theory for heat related phenomena (among many other things). Another quasiparticle is the Cooper pair, which describes two electrons coupled by a phonon. Cooper pairs describe superconductivity. For more information on quasiparticles, click this link.