Antimatter
The reason this is important to understand antimatter is because scientists found that when matter and antimatter touch each other, the amount of energy that is released comes very close to the amount of energy  says should be all together in those two pieces. The reason is that each particle of matter, when it touches its antiparticle in the antimatter world, both change over into pure energy, or annihilate each other. This release of such a high amount of energy is why a lot of science fiction writers use antimatter for fuel in their stories. For example, author Dan Brown uses antimatter in "Angels and Demons" as a very powerful weapon. It is also being looked at as a fuel source for real-life missions to outer space in the future.