What causes gravity? How does something cause something to attract? What is the cause of this universal force?

No one knows. There are some theories, but untested. That is one of the things the Large Hadron Collider is to answer.

The answer, according to Einstein, is that all mass causes a bend in the fabric of the universe itself. In this bend, a person who was moving in a straight line is actually attracted to the mass, because the shape of space itself has changed and straight isn't straight in that part of the universe anymore.

As an earlier poster already said the Large Hadron Collider is looking to solve this problem as we speak. But to be more specific, what the LHC is attempting to do is find a theoretical (has yet to be seen) particle known as the higgs boson particle, which is the supposedly what gives everything its mass.
I'm basing most of this on memory, so I'm sorry if I was off on anything.

some forces are due to unknown reasons science also doesnot know these answers these forces are called vital forces which are due to unknown reasons

Gravity is due to a rhythm (a vibration) and how it plugs into space-time. The base of gravity originates from the invariant, which is its unchanging source. When atoms are attached to each other, they create a field. They conspire to sing one song, tending more towards repetition and stasis in a given place (like a group of connected people who all basically think and feel the same thing).

The degree of rhythmic change in a system determines it's gravity, not mass. When lots of atoms are conjoined they limit possibilities in an area of space-time. This amounts to a limit on position, and a dense field of rhythm is created--the degrees of rhythmic freedom are thus limited. The amount of gravity in a star can be created in a single atom, it simply depends on its rhythmic disposition.

If you want to create gravity, simply repeat a rhythm continuously, as slow as possible. Eliminate all other interference. Tighten the focus down to one repetitive pulse.

The gravitational depression in space-time (caused by an object) is due to rhythmic repetition, which creates a well. This draws in other energies, changing them into a force more similiar to gravity. Since empty space is not naturally and intially constrained in its degrees of freedom, this means space-time is thereby warped by gravity itself.

Change is the opposite of gravity, basically. How close a rhythm is to absence of change determines gravitational force. If it is close to no change, the force is strong. Gravity is about density in position. It's about going from superposition to a more definite and local position.

Gravity is part of quantum uncertainty also, because it inhabits niches which display varying degrees of density.

Rhythm becomes more important than space when determining the ultimate position in reality. For example, if you have an empty room (that has coordinates), then add a group of atoms to a particular section of a grid, that is not what is most significant as far as space-time is concerned. The rhythm of the atoms is what determines the placement in space-time, not just the coordinates on a grid.