Ever wondered why two positive charges repel each other? It turns out that tiny particles called bosons are responsible for that. Each positively charged particle is constantly giving off photons, which are the particles that make up light: when one of those photons hits another positively charged particle, it gets absorbed, with the effect of pushing the particle forward. The combined effect of the emission and absorption of these photons looks like there’s a repulsive force between them. Photons are a type of boson: each force has its own.
So far physicists have discovered four fundamental forces, each one with its own bosons that transmit it. Here’s a quick summary of them:
The gravitational force is transmitted by a theoretical particle called the graviton, which has never been observed. In fact, nobody has been able to come up with a viable quantum theory of gravity so far. Maybe a surprise is in store, although most physicists are convinced the graviton has to exist.
There are two other forces most people are not familiar with: the strong and weak nuclear forces. The strong nuclear force is responsible for keeping atomic nuclei together: without it, the repulsion between the protons that make them up would instantly disintegrate it. Its boson is called the gluon. The weak nuclear force is mediated by three different particles, which behave like heavy copies of the photon. The W+ and the W– are charged, whereas the Z0 is neutral, just like a photon.