In a nutshell, the main difference between a theory of everything and string theory lies in their scope and approach.
A theory of everything, also known as a unified field theory, is a hypothetical framework that aims to explain all the fundamental forces and particles in the universe within a single, consistent mathematical framework. It seeks to unify the four fundamental forces of nature: gravity, electromagnetism, and the strong and weak nuclear forces. A theory of everything would provide a comprehensive understanding of the fundamental laws governing the universe.
On the other hand, string theory is a specific approach within theoretical physics that attempts to describe the fundamental building blocks of the universe as tiny, vibrating strings. In string theory, particles are not considered point-like objects but rather tiny loops or strings. These strings vibrate at different frequencies, giving rise to different types of particles. String theory emerged as a potential candidate for a theory of everything because it has the potential to unify all known forces and particles.
However, it's important to note that string theory has not yet been proven experimentally, and there is ongoing debate and research in the scientific community regarding its validity. String theory has also evolved into various formulations, such as M-theory and superstring theory, which aim to incorporate different aspects and dimensions of the universe.
In summary, a theory of everything is a broad concept that seeks to explain all fundamental forces and particles in the universe within a single framework, while string theory is a specific approach within theoretical physics that has been proposed as a potential candidate for a theory of everything.