Einstein comes along and says, space and time can warp and curve, that’s what gravity is. Now string theory comes along and says, yes, gravity, quantum mechanics, electromagnetism — all together in one package, but only if the universe has more dimensions than the ones that we see.

Source: "Making Sense of String Theory." TED2005. Feb. 2005. Conference Presentation. Additional Information: This quote is from physicist Brian Greene's 2012 TED Talk about the superstring theory, a so-called "theory of everything" or ultimate theory of the universe. The quote explains the history of how this theory came about -- first, Einstein theorized about space, time and gravity, and later on, physicists were able to incorporate Einstein's theories into a larger framework, whose "catch" is that it states that the universe must have more dimensions than we previously thought (10 dimensions of space and 1 dimension of time). Watch the full TED Talk here: Brian Greene - Making Sense of String Theory

“Making Sense of String Theory.” TED2005. Feb. 2005. Conference Presentation.