The Four Fundamental Forces - These four forces are the key sections of modern physics theories and models. They are: Gravity (explained earlier), Electromagnetism, Strong and Weak Nuclear forces. Electromagnetism is the attraction of atoms through electrons and protons (negative and positive forces in the atoms), or lack thereof, and the transfer of electrons between atoms. Strong nuclear forces are what keeps atoms together, it is what forms the bond between protons and neutrons. Weak nuclear force is responsible for radioactive decay. It is when an atom loses energy in its nucleus by emitting radiation through alpha, beta, gamma rays, or neutrinos.