My name is James Lincoln. I'm a physics teacher here for About.com. Today we're going to talk about Unified Field Theory. In physics, sometimes one theory gets unified with another. For example, in the 1800s, it was discovered that electricity and magnetism were one and the same phenomenon. That is, there was an experiment where electricity made magnetism. So those two were unified together into a single theory. More recently, radioactivity has been unified with electromagnetism. That is, the weak force that breaks the nucleus apart has been unified theoretically with electromagnetism. But it couldn't explain what was necessary to hold the nucleus of atoms together, which is the strong force that holds them together. Even more recently, the strong force theory has been unified with the electro-weak theory. So now we have three together. But what's missing is a theory of gravity. That is, mass and gravity have not been unified into a complete theory. So it's the goal of unification schemes to unite theories into one larger theory. And currently what's missing is a unified theory of gravitation, electromagnetism and the strong and weak force. This would be a grand unified theory or a theory of everything. And that's one of the goals of high energy particle physics.I'm James Lincoln for About.com. Thanks for watching.