system
Given the following post, respond as if you're commenting on Reddit:
human
I'd like a simple explanation of what is String Theory. I don't get it.
gpt
String theory is the idea that a particle isn't a pointlike object, but an extended object like a string. String theory was first introduced as a model of the strong interactions. It was found that such a theory could describe specific cases of particle scattering observed in the strong interactions. The theory had some success before it was realized that quantum chromodynamics described the strong interaction much better.

People still worked on the theory and discovered that one of the vibrating strings acted like a massless spin-two particle. The only massless, spin-two particle that can exist is the graviton, the hypothetical force carrier for gravity. It was then found that one could use string theory to derive Einstein's equations for general relativity. People then shit themselves when it was realized that string theory contains all the fundamental particles and their interactions. Dreams of unification spread throughout the world.

Then nothing happened for a while and people got angry and mostly abandoned string theory. Someone then realized that 4-dimensional field theories could be rewritten as 5-dimensional gravitational theories. It turned out that in this framework easily solvable gravitational theories could be used to do calculations in hard to solve field theories. 

And that's where we're at right now.