Four Fundamental Forces: One of the four fundamental forces is Gravity, which is unlike the other three forces because it relates to the theory of General Relativity. The other three forces concern Quantum Mechanics. Electromagnetism which is one of the strongest forces is followed by weaker force called Strong Nuclear, that is responsible for keeping the nucleus of the atom together. Lastly there is Weak Nuclear that causes radioactive decay. (add strength and distances)
General Relativity: In 11/25/1915 Einstein published a paper about General Relativity. It describes "space-time". There is a giant blanket in the universe and when a object rest on it the blanket conforms to its shape. The "steepness" of the dent int he blanket is attraction of gravity. The heavier the object the "steeper" the dent creating a stronger gravitational pull. Depending on how strong the gravitational pull is even space and time can be influenced by it. Gravity effects all things in the universe but the strength varies.
Quantum Mechanics: Neil Bohr proclaimed that probability ruled the microscopic world. Quantum mechanics is the study of very small particles and is not influenced by gravity. But rather electromagnetism, strong nuclear, and weak nuclear in order to describe the forces within such small particles.
An example of this would be you could walk into a wall for almost an eternity before you got even the slightest chance of phasing straight through it.
Unification: In terms of math Quantum mechanics and general relativity they do no coincide with one another. This is partly due to the fact that general relativity concerns massive objects such as planets and stars. Where as quantum mechanics focuses on particles the size of atoms and smaller. The forces that rule each area are completely different from another and do not apply to each other in terms of size.
String Theory: String Theory also known as "the Theory of everything" states that the universe is made up entirely of tiny strings (10^-35m) that can be closed or open ended. The formation of things strings constitutes matter. The math surrounding string theory suggest that there are many more dimensions than 3. However there may never be a way by today's standard to get any experimental evidence.