## The Four Fundamental Forces

The properties of the four fundamental forces are summarised in the following table.

 Mediating Particle Force Relative Strength Range Name Mass Charge Spin Strong 1 Short Gluon 0? 0 1 Electromagnetic Infinite Photon 0 0 1 Weak Short  80.4, 80.4, 91.2 resp 1 Gravity Infinite Graviton 0 0 2

There are several things to note:

Both gravity and the electromagnetic force have infinite range. The mediating particle of both these forces are stable and do not decay spontaneously. This means that the flux of the force particles through a sphere drawn around the source of the force is a constant no matter how big the sphere, and this implies the force must obey a law.

The weak force is mediated by massive particles. We may find the approximate range of the weak force using Heisenberg's Uncertainty Principle for virtual particles    We can estimate the range of the force now by assuming the force particles travel at the speed of light for this time. This approach is general and can be used to estimate the range of forces from the masses of the mediating particle. 