Almost all fundamental interaction in which gravity is also included, are a part of string theory. Thus, almost all theorists and physicists believe that string theory is a theory of everything and is able to describe anything that is a part of our universe. Currently research on string theory is being conducted in order to find a valid solution to the many problems related to micro elementary particles that has small cosmological constants. These constants contain dark matter and a cosmic inflation mechanism. Progress has been made in order to achieve these goals. Hence, it is not clear if the string theory is really a universal theory or not. As described above string theory has not yet managed to give a complete definition for a certain thing that can be applied in any situation or circumstances. This is said to be a big fallback for string theory. Until now string, theory is being applied using a perturbative approach. It is not yet discovered how to apply this theory non-pertubatively. To understand these statements it is important to understand fundamentals of string theory.
