Theory of everything

There are two theoretical frameworks that emerged in the 20th century that together most closely resemble a theory of everything: general relativity and quantum mechanics. General relativity is applicable to understand gravity and the large scale structures in the cosmos, such as stars, galaxies and clusters of galaxies. Quantum mechanics, on the other hand, uses principles of probability to describe electromagnetism, the strong and weak nuclear forces at the atomic and subatomic scales. Both of these theories are remarkably applicable in their own domains, however, at regions of small scale and high mass, such as at a black hole singularity or the instant of the Big Bang, the theories cannot be harmoniously integrated together as would be hoped. A deeper synthesis of general relativity and quantum mechanics is necessary. This is why we say that a theory of everything, like string theory, would be able to describe all physical phenomenon in the universe. Quantum gravity has become an area of active research in pursuit of this goal.