Loop quantum gravity (LQG) is a theory of quantum gravity, merging quantum mechanics and general relativity. Its goal unifies gravity in a common theoretical framework with the other three fundamental forces of nature, beginning with relativity and adding quantum features. It competes with string theory that begins with quantum field theory and adds gravity. From the point of view of Albert Einstein's theory, all attempts to treat gravity as another quantum force equal in importance to electromagnetism and the nuclear forces have failed. According to Einstein, gravity is not a force – it is...

Electric charge is the physical property of matter that causes it to experience a force when placed in an electromagnetic field. There are two types of electric charges; positive and negative (commonly carried by protons and electrons respectively). Like charges repel and unlike attract. An object with an absence of net charge is referred to as neutral. Early knowledge of how charged substances interact is now called classical electrodynamics, and is still accurate for problems that don't require consideration of quantum effects. Electric charge is a conserved property; the net charge of an isolated...