Why has no one unified the 4 fundamental forces? What are the key differences?
1 Answer
The fundamental forces haven't been unified because we don't yet have a theory which can do this.
Explanation:
The electromagnetic force describes the interactions between charged particles. The photon mediates the force and is responsible for creating electric and magnetic fields. Electricity and magnetism were thought to be separate forces until Maxwell showed that they were related.
The weak nuclear force is responsible for radioactive beta decay. For example it can convert a neutron into a proton, an electron and an electron antineutrino. The weak nuclear force is mediated by the W and Z bosons.
The electromagnetic and weak forces have been unified into the electroweak force. It has been proved that at very high energies the photon and the Z boson are indistinguishable. It was the discovery of the W and Z bosons which confirmed the electroweak theory.
The residual strong nuclear force is responsible for binding protons and neutrons together to form an atomic nucleus. The force is mediated by gluons. The residual strong nuclear force is actually a residual effect of the colour force which binds quarks into mesons and baryons.
We don't yet have a Grand Unified Theory (GUT) which unifies the electroweak force with the strong nuclear force. There have been a number of GUT candidate theories. They require the discovery of new particles to confirm the theories. One problem is that the unification will happen at very high energies which would require particle accelerators which we don't have the technology to build.
The electromagnetic, weak and strong forces are described by quantum theories. There is no quantum theory of gravity. In fact Einstein showed that gravity is the result of the curvature of 4 dimensional spacetime by masses.
The unification of all four forces requires a Theory of Everything. This can't happen until we have a GUT and have a quantum gravity theory.
