From an early age I thought that scientists knew what gravity is, the actual thing and not just the effect it has on us. One time, to my disbelief, I read somewhere that we do not know what it is. I actually have no memory of where I heard that we don't know what it is. Anyway, for the rest of my life from when I discovered that we don't know what gravity is till now, I have just assumed that that was true. We don't know. However, I recently had a teacher who said we do know what gravity is, I forget his explanation though. So my question is: Do we know what gravity is? If so, what is it? If not, why don't we know, and what do we need to find out? thank you in advance.