Hi, I'm John Skieswanne, and this post is part 4 of a series on physics. In this series I will explain a few pillars of modern physics. I won't be
using any complex maths. It is my hope that this series will introduce some of you brilliant, curious-minded laymen out there to the inner circles of
So, sit back and enjoy.
The Standard Model of Particle Physics.
What is the irreducible components of the Universe? If it's made of gases and atoms and stars and rocks, are all of these made of something smaller?
The answer, of course, is yes. It turns out that everything is indeed made of incredibly small components called "elementary particles". They are
the Universe's DNA. Even your DNA's DNA, for that matters. These components build up atoms, electrical currents, even forces such as light and
inertia. And now you're going to meet all 17 of them.
The first particle ever discovered was the electron
in 1897, by Joseph John Thompson's team. The later even published a good approximation of
the electron's mass and electric charge. This elementary particle is responsible for electrical currents. Electrons are also found surrounding the
atom's nucleus. Alternatively, a heavy version of the electron, called the muon
, was spotted by Carl David Anderson in 1936. The atomic
nucleus itself was discovered to contain neutrons and protons - and, later, protons were proposed to be composed of three quarks (two up
and one down
quark) while neutrons were proposed to be composed of three quarks (one up and two downs). Later on, strange particles were
discovered (for instance kaons) which were a combinaison of a strange
quark with either an up quark or a down quark. In 1974 the J meson was
discovered, which were composed of charm
quarks. An even heavier electron (the tauon
), along with top
quarks, were discovered in the 70s (and in the 90s for the top quark). A neutrino
for the electron, the muon and the tauon were
observed to exist - they act a bit like their respective particle's luggages. When a particle decays and emits an electron, it was observed that some
energy was missing, so it was proposed that a neutrino was carrying it away. Gluons
were proposed to "glue" quarks together. Photons
are particles of light. To explain particle decay (only a few particles can survive for longer than a fraction of a second), the W boson
the Z boson
were introduced. And, most recently, the Higgs boson
was introduced to account for the inertia of the particles. The latter
acts a bit like a molasses which cling on a particle and give it mass. All forces in the Standard Model are explained with mathematical equations,
called Special unitary groups (SU).
There you have it: 17 particles. Together these particles build up anything from the exotic Cascade B baryon to Stars, including DNA, drops of water,
mountains, whole planets.
3 of these particles have an electric charge of -1 (that is, their electrical charge is equal to that of an electron): the electron, the muon, and the
Out of the 14 remaining, three other particles have an electric charge of +2/3 (that is, their electrical charge is equal to 2/3 of an electron, and
has the opposite sign): the up quark, the charm quark, and the top quark.
Out of the 11 particles remaining, three other particles have an electric charge of -1/3 (that is, their electrical charge is equal to 1/3 that of an
electron): the down quark, the strange quark, and the bottom quark.
W bosons have a charge of either -1 or +1, depending on the parent particle as the latter undergoes decay.
All other 7 particles have zero electric charge.
All particles (well, except the Higgs boson) have spin. The spin is the rotation of a particle on itself (as particles travel, they spin on
themselves, like a bullet does after it's been fired from a rifle) - half a spin means that the particle looks the same after 1/2 rotation. A spin of
1 means the particle basically looks the same all over. Elementary particles with an integer spin are called "bosons", and usually they carry
forces. Particles with half a spin are called "fermions", and they compose matter. There are 12 fermions in the Standard Model. The rest are bosons.
Particles were also observed to have mass, although we don't know for sure what's the mass of any neutrinos (only that it's below a certain value).
Usually the mass of most particles is measured in a special unit called Mega electronVolt (MeV). 1 MeV is equal to 1.782 octillionth of a gram, or
Fermions which are the most normal and were discovered first, in other words, the electron, its neutrino, the up quark and the down quark, are said to
be "first-generation particles".
Fermions which were discovered a bit later, were more massive and thus were more prone to decay very fast, such as the muon (heavy version of the
electron), its neutrino, the charm quark (heavy version of the up quark) and the strange quark (heavy version of the down quark), are very rare on
Earth and they are said to be "second generation particles".
Finally, super-heavy particles which were discovered last, whose mass are such that they are impossible to find unless you own a CERN-class particle
accelerator, and which decay even more quickly than Generation 2 particles, include the tauon (super-heavy version of the electron), its neutrino, the
top quark (super-heavy version of the up quark) and the bottom quark (super-heavy version of the down quark). These are said to be "third generation