The grand unified theory (GUTis a sought-after model that would unify three of the four forces of nature. Which force is the one it would not include?"

Elementary particles, also known as fundamental particles, are subatomic particles that are not made up of other particles. They are smaller than an atom and do not appear to be made up of a combination of more basic things. 
The Standard Model recognizes 17 distinct particles, including 12 fermions and five bosons.