We have definitely come a long way since the days when we thought the planets revolved around us and when gravity was just the force that made things fall. Yet, as we said at the beginning of this section, there is still much more that we do not know, and much more we can learn.
General relativity is certainly a very good theory but it cannot last forever. As you know, it describes gravity and the structure of the universe on a large scale. However, the theory that we use to describe structures on a small scale, quantum mechanics, is known to contradict general relativity in certain ways. The two theories cannot both be right.
Many would say that the main goal of physics today is to combine general relativity and quantum mechanics into one grand unified theory that describes the structure of the universe on all scales. Doing this would involve unifying gravity with the other three fundamental interactions (electromagnetism and the strong and weak nuclear forces). You see, it has been strongly speculated that all four of these interactions are simply different aspects of a single force. So it may be that in the future we will see gravity as just one part of a larger force, a force that is responsible for all the interactions between matter. Only time will tell.
For more on the fundamental interactions see What is Gravity? Page 3.
