Photons are mediators of the electromagnetic interaction, Z and W bosons transmit weak interaction, and gluons are carriers of the strong interaction. The name given to the initial instant of the expanding universe theory, in which the universe begins as an infinitely dense and hot medium. Big Bang is supposed to be a kind of explosion out of which all the matter in the universe was generated. Forces act on otherwise free to move objects, changing their velocities. Every energetic object is subject to the gravity force.
Electromagnetic force causes interaction between electricaly charged objects.
Weak force acts between weak charges and is responcible for the nuclear decay reactions. Strong force acts between colour charges in quarks and gluons , binding them into protons , neutrons and other particles . The action of a force is called interaction, thus there are four types of interactions, corresponding to each fundamental force. A theory which embodies all of our current understanding about the behaviour of fundamental particles. It is widely tested and is accepted as an accurate description at the currently available energies by particle physicists.