Physicists have put gravitation into a group of forces called the four fundamental interactions. These interactions, which also include the strong nuclear force, the weak nuclear force, and electromagnetism, are responsible for all of the forces exchanged between matter particles.
Although we think of gravity as rather powerful, it is, ironically enough, the weakest of all the fundamental interactions. It is so weak in fact, that we would probably never even know of its existence if it weren’t for two special qualities. First, gravity is always attractive. This gives it an advantage over a force like electromagnetism which can be attractive or repulsive and therefore tends to cancel itself out. Second, it can act over very large distances. Whereas a force like the strong nuclear force can’t even reach from atom to atom, gravity’s attractive powers can stretch across almost infinite amounts of space.What all this means is that although gravity is too weak to produce noticeable effects between small objects like a table and a chair (which is why you don’t see things like these clinging together), the combined gravitational forces between two very massive objects, like the Earth and the Sun, can be incredibly strong indeed.
For more on how our theories concerning the fundamental interactions may evolve in the future see History Page 8.
