A fundamental interaction is a mechanism by which particles interact with each other, and which cannot be explained by another more fundamental interaction. Every observed physical phenomenon, from galaxies colliding with each other to quarks vibrating inside a proton, can thus be explained by these interactions. Because of their fundamental importance, understanding of these interactions has occupied the attention of physicists for over half a century and continues to do so.
Traditionally, modern physicists have counted four fundamental interactions:
- the weak interaction
- and the strong interaction
Their magnitude and behavior vary greatly, as can be seen in the table below. Yet, it is strongly believed that three of these interactions are manifestations of a single, more fundamental, interaction, just as electricity and magnetism are now understood as two aspects of the electromagnetic interaction. Electromagnetism and the weak nuclear forces have been shown to be two aspects of a single electroweak interaction at low energy limit.
Grand unified theories seek to unify the electroweak force and the strong nuclear interaction, but none have been validated experiementally. The topic of unifying gravitation with the other three into an interaction that is completely universal seeks to express gravity as the electromagnet property of systems of moving mass and energy. The web of electromagnetic energy that binds all matter and energy in this and other universes is currently being pursued as String Theory and Dark Matter. This spider-like web of electromagnetic energy reaches a hurricane-type vortex inside of Black Holes as it crosses the bounds of infinity. On the other side is Dark Matter.