Axions are considered one the best candidates for dark matter because they are super-light particles and their existence is a solution to the problem created by Quantum Chromodynamics and symmetry breaking. Quantum Chromodynamics is the theory that quarks have another quantity in addition to the electric charge called color which characterizes how quarks interact with each other. The axion begins its life massless and that means that there was any number of them at the Big Bang. Because of this, there is an expected constant background density of axions throughout the Universe that could be dark matter. They are a good dark matter candidate because they are a stable particle, electrically neutral, have strong interactions with matter, and interact with gravity. Their existence upholds Einstein’s equations of gravity and they are about \(1 \cdot 10^{-5}\) eV, so nearly massless. There are many experiments looking for axions, but so far none have been found. (7)