Over the last several class periods, we have talked a lot about the force of gravitation. Incidentally, gravitation is considered one of the four fundamental forces of nature, along with weak force, strong force, and electromagnetic force. Interestingly, though, gravitation is the only one of these that is explained by a separate theory—the general theory of relativity—than the other three, which are covered in the theory of quantum mechanics.
Because this apparent inconsistency is frustrating and probably an indication that the theories are incomplete, scientists have put some effort into developing a “theory of everything“, i.e. a singular theoretical framework of physics that would explain all of these forces together. Since about the 1960s, string theory has been developed, and it naturally explains all four fundamental fources within one framework. It has become the most likely contender for an accepted theory of everything.