Theory of Everthing

[The Cosmic Inquirer]

One of the main and recurring obstacles in attempting to formulate a Theory of Everything is that it is very difficult to incorporate gravity with the other three fundamental forces of the universe (i.e. the strong nuclear force, the weak nuclear force, and electromagnetism).  To date only string theory (and its latest rendition M-Theory) has been able to do this.  My inquiry is this: Why are physicists trying to incorporate gravity into a theory of everything when it is not a fundamental force of nature?  To clarify, what I mean by gravity not being a fundamental force of nature is that, described by Einstein in his General Theory of Relativity, gravity is just a property of the curvature of warped space-time (i.e. I postulate that gravity cannot exist with out space-time).  Thank you for your consideration and time.

[Physics_Hacker]

Gravity is a fundamental force of nature, its effects just create the curvature of spacetime we see; its like a map of electromagnetic fields being the same as "spacetime maps", thy just have to be presented differently. There are particles of gravity, and they create the bending in space time. The problem is, the particles might be able to move out of our four dimensions and so they are...different. In string theory, all particles are attached the brane that is our universe, except gravitons, which can "float"between them. This causes problems because its not similar to the other particles.
My point is, they're incorporating gravity into a Theory of Everything because it is a fundamental force, its just very, very different from the others.

[The Cosmic Inquirer]

Thank you Physics_Hacker.  I understand the many intricacies of string theory including that gravitons can "float" between dimensions (my understanding of string theory was enhanced greatly by the book "Parallel Worlds" by Michio Kaku).  It had just always appeared to me that the warping of space-time is caused by matter, such as the Sun for example, not that the gravity of the Sun warped space-time (I had thought the warping of space-time is what caused gravity [through my interpretation of General Relativity]).  Thank you for your answer.