22.1. The Big Idea http://www.ck12.org
22.1 The Big Idea
All matter is composed of fundamental building blocks, called the elementary particles. These building blocks are
much smaller than an atom, and so are sometimes referred to assubatomicparticles. Particles interact with one
another according to a set of laws based on symmetries in the universe. There are two types of particles: force
particles (bosons) and matter particles (fermions). What sets them apart is an intrinsic property called ’spin’. Force
particles have integer spin values (1,2,3,...) and matter particles have half integer spin values (1/2,3/2, ...). The set
of particles and the laws that govern their interactions are called the Standard Model. The Standard Model is very
powerful and can predict particle interactions to amazing accuracy.
The fifth of the five conservation laws is called CPT symmetry. The law states that if you reverse the spatial coordi-
nates of a particle, change it from matter to anti-matter, and reverse it in time the new object is now indistinguishable
from the original. More on the fifth conservation law in the Feynman Diagram’s chapter.
MEDIA
Click image to the left for more content.MEDIA
Click image to the left for more content.Matter
- Particles can be grouped into two camps:fermionsandbosons.Typically matter is made up of fermions, while
interactions (which lead to forces of nature such as gravity and electromagnetism) occur through the exchange
of particles called bosons. (There are exceptions to this.) Electrons and protons are fermions, while photons
(light particles) are bosons and transmit the electromagnetic force (known as QED in particle physics). - Fermions (matter particles) can be broken into two groups:leptonsandquarks.Each of these groups comes
in three families. - The first family of leptons consists of theelectronand theelectron neutrino.The second family consists of the
muonand themuon neutrino.The third consists of thetauand thetau neutrino.Particles in each successive
family are more massive than the family before it. - The first family of quarks consists of the up and down quark. The second family consists of the charm and
strange quarks. The third family consists of the top and bottom quarks. - Up and down quarks combine (via the strong force) to form nucleons. Two ups and a down quark make a
proton, while an up quark and two down quarks make a neutron. Different combinations of quarks are called