Introduction
Curved Space-Time

You have probably learned in school that gravity is a force. In fact, gravity is not a force at all, according to Albert Einstein! Without gravity, space would be flat. Gravity actually curves, or "warps," space. The more dense the matter is, the more the space around it is curved. Not only are objects themselves curved, but the space around them is curved as well. You may be wondering in what direction the space is curved. It is curved into the fourth dimension! (NOTE: This fourth dimension is not the fourth dimension in space-time, the way Einstein described it, where three dimensions are the normal space dimensions and the fourth is time. This fourth dimension is a fourth spatial dimension.)