EINSTEIN'S GENERAL RELATIVITY
Albert Einstein's general theory of relativity is one of the towering achievements of 20th-century physics. Published in 1916, it explains that what we perceive as the force of gravity in fact arises from the curvature of space and time. Einstein proposed that objects such as the sun and the Earth change this geometry.
String theory is suggested to be the theory of everything. The theory tells us that everything is made up of extremely small strings. These Strings are so small that they are thought to be 10^-35. You are unable to see these strings but the math for this theory suggests that these do exist and are the makeup of everything around us. This theory tells us that there are many different universes that have different realities.
Quantum mechanics largely involves probability. It is believed that one cannot know the outcome, only the probability of the outcome. It describes how the universe works at the subatomic level and explains all of the fundamental forces at a subatomic level aside from gravity. Quantum mechanics is the branch of mechanics that deals with the mathematical description of the motion and interaction of subatomic particles. Quantum mechanics is the science of what is very small.
Albert Einstein longed for a single equation that explained the entire universe into it. Unfortunately, he died before he could achieve it. Physicists were able to combine electromagnetic, strong nuclear, and weak forces into one equation, but not gravity. An equation for unification was theorized. However, there were anomalies, meaning that it wasn't true. In 1984, the matching numbers of "496" on both sides of the equation indicated that the anomalies were gone and the unification equation was true. All four forces could be combined into a single equation. This is known as "The Theory of Everything".