Particle Physics Follow Up
The book presents an elegant simultaneous solution to three questions:
- How can the strong force possibly get more powerful with distance?
- Why can’t we break protons into their component quarks?
- Where the heck does a proton’s mass really come from?
In fact, Wilczek won a Nobel Prize for the solution. First, you have to understand three basic facts of physics:
- Quantum mechanics says that short-lived particles and their anti-particles are constantly popping in and out of existence.
- Protons are made up of 2 up quarks and 1 down quark. These three quarks have different primary color charges (RGB) so that together, they are color neutral (white).
- Quantum mechanics says it takes a tremendous amount of energy to constrain the location of a particle (AKA the uncertainty principle).
With electric charge, the cloud of particles from (1) screen the EM force. Assume you have a proton out in space. A particle-antiparticle particle appear. There is no net energy or charge created. However, the negative particle will move a little bit towards the proton and the positive charge will move a little bit away from the proton before they annihilate each other. This absorbs a tiny bit of the EM force.
Wilczek and company had an idea. What if color charge works differently? What if it is anti-screened by (1). The ephemeral particles move so that the color charge gets relayed. Think of it as reinforcing a wave rather than canceling it. When they worked through the color field equations, they found a very few solutions where anti-screening was possible. This is good because it means the theory wasn’t arbitrary.
So that explains question (1) of how the strong force can get larger with distance. But if you do the integral of an ever increasing force over all points in the universe, you get a metric butt-load of energy bound up in a quark.
Here’s where (2) comes in. If you combine quarks with R, G, and B color charges, they cancel leaving no net force. Problem solved. And it explains the answer to our question (2) of why whe can’t break protons into quarks. The energy required is just too high.
But what about our question (3)–the mass of the proton? Enter the uncertainty principle. The three quarks in a proton can’t all be exactly on top of each other. That also requires too much energy. So at some point, the energy equation for the strong force increasing over distance and constraining the quantum location of the quarks balances. Plug that energy into m = E/c^2. That accounts for 95% of the mass of the proton. Most of the rest consists of the quarks’ masses themselves.