Dirac Hole Theory

This is a kinda old theory, but it doesn't stop it from being incredibly interesting. It is one of the theories that explains matter and antimatter. Though it is not experimentally confirmed, it is intuitive and give a good sense of antimatter's identity.

Let's start with introducing energy levels. A particle can exist in discrete energy levels (or quantum states), but due to Pauli's exclusion principle, no more than two electrons can occupy the same energy level (and the two electrons have to have different spins).

Paul Dirac found that the when the equation for energy is applied to electrons, then the energy for an electron could be both positive and negative (there is a square invovled). Then, it is logical to assume that energy levels extend infinitely above and below the "zero level". For all positive quantum states (associated with positive energy), there will be some kind of negative energy level.

Nature, in it's nature, is lazy. It tends to lower energy states. So, what is preventing the particle to drop to lower and lower energy levels and releasing an infinite amount of energy?

Dirac believed that all negative energy levels are occupied by an infinite sea of electrons. Everywhere. Even in a vauum. This "sea" is known as the Dirac sea. Like this. With the Dirac sea, any electrons above them would not fall further down because they are only able to "float on top" of the Dirac sea.

Astute readers would be alarmed by our apparent incapability to sense those electrons in the sea. Well, as the electrons are evenly distributed, we don't see their effects. There is no force, no moment, nothing for us to detect. When we notice an electron, it is actually lying on top of the Dirac sea.

Particle interactions

When external energy (e.g. a gamma photon) interact with an electron in the Dirac sea, if it has energy equal or bigger than twice m_0c^2 (m_0 is the rest mass), the electron can jump into a higher energy level. When this happen, there will be a "hole" in the sea and an electron above the sea. You guessed it. The "hole" in the negative energy electrons is the positron. This is pair creation!!

The reverse process, pair annihilation, is also possible. An electron jumps to a lower existing "hole", releasing energy as it falls through the energy levels. The energy is released in the form of gamma photons (two, as linear momentum should be conserved!)

References:

https://www.youtube.com/watch?v=IexNXyyYfYk