How are the four fundamental forces similar?
1 Answer
Symmetries!
Explanation:
The four forces are electromagnetic, nuclear weak, nuclear strong and gravitational.
Between the '30s and the ''70s physicists realised that the forces are the expression of something deeper in the nature: symmetries.
If we describe the motion of a particle looking it from the front or from the back of its motion, the motion will be the same. We call this symmetry, because the equations are symmetric under the transformation that sends my observation point from the front to the back.
Today we know that the particles are symmetric under very precise set of transformations. For example all the particles are symmetric under the transformations discovered by Einstein in the Special Theory of Relativity (called transformation of Lorentz because Lorentz discovered them before, but Einstein applied them to the dynamics).
The scientists discovered that some of the symmetries does not belong to a single particle but needs groups of particles.
So, for example, two electrons together can almost be symmetric under a special symmetry that we call U(1). They are not perfectly symmetric, something is missing. Then if you add the piece missing in the equation, you discover that the missing part represents another particle that we call photon.
So two electrons and a photon are together symmetric and we call this electromagnetic force.
This was a great discovery because it was the first time that we obtained a force as expression of something purely mathematical.
Scientist applied the same idea to the weak force and discovered that the symmetry of that force can be completed with three different particles,
More than this, the weak interaction is of the same nature of the electromagnetic force and at high energy the symmetry is the same.
Today we should call this force electromagneticweak force. On some book it is called electroweak force.
The same theory is today applied to the strong interaction and the scientists are on the good track to understand which symmetry is generating that force and how this is connected to the electromagnetic symmetry and the weak symmetry.
We expect to found one day that these three forces are in reality only one.
The discussion is completely different for the gravity. Gravity talks about space and time, and today nobody knows how to describe the gravity in terms of particles. This makes very difficult to adapt the symmetry idea to that force and we do not know if in reality also gravity is part of the same force or not.
To include the gravity in the same framework we need some new physics not yet discovered or experimented.
