At the moment there are only four fundamental forces known to exist – gravity, the electromagnetic force, the strong nuclear force and the weak force Other apparently distinct forces are in fact only different manifestations of these fundamental forces. For example

All four fundamental reactions are mediated by exchange particles. Essentially the exchange particles carry the force from one particle that experiences the force to another particle that experiences the force. Each force has it's own exchange particle, and each exchange particle has a range which is determined by it's mass – the larger the mass, the shorter the range of the force. If the exchange particle has zero mass, the force has infinite range. This is the case for the photon, which mediates the electric force, and the graviton, which mediates the gravitational force. The range of a force decreases with increasing mass of the exchange particle because the energy of the exchange particle must be 'borrowed' from empty space. Since energy increases with mass (), high mass particles have higher energy, which can not be borrowed as long as for short mass particles.

A summary of properties is given in the table below.

Interaction

Relative Strength

Range

Exchange Particle

Strong

1

Gluons (8 different types)

Electromagnet

Infinite

Photon

Weak

Gravity

Infinite

graviton