Elementary particles 
In the past people thought that atoms were unbreakable, so the hydrogen atom was considered the smallest particle. At the start of the twentieth century, however, it was discovered that atoms are made up of protons, neutrons and electrons. Today we know that the electron is really indivisible and so fundamental, however protons and neutrons appear to be built out of much smaller particles: quarks. The science that studies these very small particles is called Quantum Mechanics. A good understanding of the Quantum Mechanics gives us a better insight in the physics of the universe.

The families of the elementary particles.
Protons, neutrons and electrons are only three of the more than 200 subatomic particles that are known. These elementary particles, the most basic physical constituents of the universe, that help determine the four fundamental forces.

In modern physics the elementary particles are described by the Standard Model, categorized in three basic families: The electron-like, the muon-like and the tau-like.

Every family has four members, two leptons and two quarks. For every type of particle of one family there is a similar particle from the other two families, that only differ in mass.

An essential difference between quarks and leptons is their electrical charge. The charge of a quark is 1/3 or 2/3 times the charge of an electron and can be either positive or negative. Leptons are of the same charge as the electron (-1) or carry no charge at all (neutrino's).

The Standard Model.
The Standard model is the ruling model that describes the world of the subatomic particles and interactions.
LEPTONS
QUARKS
Matter- particles: 
all common particles		 Electron 
Charge: -1 
Responsible for electricity and chemical reactions.		 Electron-neutrino 
Charge: none. 
Also possibly no mass. 
Move by billions per second through our body.		 Quark-Up 
Charge: +2/3. 
Protons contain two, neutrons one.		 Quark-Down 
Charge: -1/3. 
Protons contain one, neutrons two.
These particles existed immediately after the Big Bang. 
Now they are found by nature only in cosmic radiation.		 Muon 
A more heavy variant of the electron. 
Exists only one two millionth part of a second.		 Muon-neutrino 
Comes into existence together with muons when particles fall apart.		 Quark-Charm 
More heavy relation of the up-quark.		 Quark-Strange 
More heavy relation of the down-quark.
Tau 
More heavy than Muon. 
Very unstable.		 Tau-neutrino 
Not yet discovered. The existence is assumed.		 Quark-Top 
More heavy than Charm.		 Quark-Bottom 
More heavy than Strange.
 
Force- particles: 
Bearers of the four fundamental interactions of nature.		 Gluons 

Bearers of the strong nuclear force of quarks.

 Photons 

Light particles. 
Bearers of the electromagnetic force.

 Intermediate vector bosons 
W and Z particles. 
Bearers of the weak nuclear forces.		 Gravitons 

Bearers of the gravitational forces. 
Hypothetical, Gravitons are not yet discovered.
After: Natuur en Techniek 9, 1997. The release of nuclear energy during nuclear reactions is a result of the strong nuclear force. Electricity, magnetism and chemistry are results of the electro-magnetic force. Some forms of radioactivity are a result of the weak nuclear force. Our experience of 'weight' is a result of the gravitational force.

Fundamental forces.
All four elementary matter particles interact with one another through the four fundamental forces: gravitation, electromagnetism and two types of nuclear forces, weak and strong. Three fundamental forces are described by the Standard model. Gravitation is not yet part of this model, the reason for this is that this force is much weaker than the other three, therefore the exact determination of it is not (yet) possible. All other forces we know, like acceleration, declination, collision forces etc., are deduced from the fundamental forces.

Distance determines the strength of the force.
The relative strength of the fundamental forces is not of a constant value but depends on the distance on which the force is active. The strength of gravitational force for example varies inversely as the square if the distance. At very short distances, within the range of the sizes of the nucleus of atoms or smaller, the strengths of the electromagnetic force and the weak and strong nuclear forces are more or less equal. It is assumed that all forces originate from one and the same primitive force, this theory is called the Great Unification Theory.

Gravity is not yet described by the Standard model, this force is under normal conditions neglectable small. Einstein however, showed that when the velocity of an object or its gravitational force are very large, then gravity follows other laws than those of Newton. With very large mass gravity dominates all other forces.
 

Anti-matter.
According to the principles of relativity and quantum mechanics, for every matter particle there exists a anti-matter particle, which is in principle completely equal to the matter particle however with opposite charge. The positron for example is the anti-matter particle of the electron.

These particles are demonstrated on lab scale in so-called particle-accelerators. Here atom nuclei are brought into collision at very high velocities by which matter particles and their anti-matter particles come into being, with every neutron a anti-neutron and with every proton a anti-proton.

The strange phenomena however is that, with exceptance of some few anti-matter particles in cosmic radiation, furthermore no 'natural' anti-matter is found. Not on Earth, nor in our solar system, nor in the Milkyway or any other galaxy. This could mean that the matter in the universe might be the remains of a mixture of matter and anti-matter during the early formation of the universe, where a surplus of matter was present. If this was really the case is still one of the big questions. 

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