Theory of Everything (TOE)

Theory of Everything (TOE), in physics, theoretical framework that, if discovered, would provide a unified description of all the forces of nature. These forces, also called interactions, are gravitation, electromagnetism, the strong force (a short-range force that holds atomic nuclei together), and the weak force (the force responsible for certain radioactive processes such as beta decay). In addition to succinctly summarizing fundamental physics, a TOE might explain why the laws of physics are what they are. The American physicist Steven Weinberg has argued that a Theory of Everything would be logically isolated-that is, it could not be modified without being destroyed.
The history of physics suggests that such a final theory may be possible. The theory of gravitation formulated by the English physicist Isaac Newton in 1687 provided a unified description of the motion of the moon and the fall of an apple. Similarly, the theory of electromagnetism formulated by the British physicist James Clerk Maxwell about 1873 unified electric, magnetic, and optical phenomena. About 1968 Steven Weinberg and the Pakistani physicist Abdus Salam independently formulated the electroweak theory, which unifies the weak interaction and the electromagnetic interaction by using a mathematical technique known as gauge symmetry. Grand unification theories currently studied by physicists hint at a further unification of the electroweak and strong interaction.
Currently, the best candidate for a TOE is the theory of superstrings. In this theory, everything in the universe-all particles and forces and perhaps space-time itself-consists of fantastically small strings under immense tension, vibrating and spinning in a multi-dimensional superspace. Extra dimensions, in addition to width, depth, height, and time, are mathematically necessary to avoid tachyons (faster-than-light particles) and ghosts (particles produced with negative probability). These extra dimensions are thought to be compactified, or curled up into tiny circles, and thus rendered unobservable. Different elementary particles correspond to different quantized modes of oscillation of the string. Unfortunately, superstrings theory is very difficult to calculate with and has yet to yield testable predictions.