The Four Fundamental Forces

Once useful analogy is to think of quarks and leptons as the bricks of the universe. The universe appears to be built of these two different kinds of bricks that are arranged in different ways to make everything we see, but you cannot build a house using bricks alone. There has to be something like mortar to hold the bricks together. The “mortar” of the universe --the things that hold the elementary particles together and organize the physical universe into the structures we know--are the forces. At the moment we know of only four fundamental forces in nature. Two of these,gravity and electromagnetism were known to nineteen-century physicists and are part of our everyday experience. They are forces with infinite range--that is, objects such as starts and planets can exert these forces on each other even though they are far apart.

The other two forces are less familiar to us, because they operate in the realm of nucleus and the elementary particle. They have a range comparable to size of the nucleus (or smaller) and hence play no role in our everyday experience. The strong force holds the nucleus together, while the weak force is responsible for process such as beta decay that tear nuclei and elementary particles apart.

Each of the four fundamental forces is different from the others in strength and range. (See table below). The important point anout the four forces is that whenever anything happens in the universe, whener an object changes its motion, it happens because one or more of these forces is acting.