How does string theory unifies general relativity and quantum theory??
1 Answer
I'd be reluctant to say that string theory is a grand unification theorem. But I would say the question is valid as string theory attempts to formulate quantum gravity, which is a major missing piece for unifying quantum and classical domains.
Explanation:
String theory is theoretical. It is a framework that is useful for addressing the questions about how gravity might be reconciled in quantum mechanics.
The main idea of string theory is that all particles can be represented as one-dimensional strings. Strings are able to propagate through space and interact. Now there are many theories and versions of "what is a string?", but in general all types of string theories simply describe how strings vibrate.
The reason string theory provides a sort of "quantum gravity" formulation is that "zooming out" from a string makes it appear like a normal, standard particle. The mass, charge, and other properties of the particle are determined by the vibrational state of the string. One of the vibrational states that string theory considers creates the "graviton", which is the quantum particle that holds the gravitational force. In this way, string theory offers an idea as to how gravity might be represented in the quantum realm.
