If you'd been reading "Angels & Demons" you should have come across the term - Anti-Matter. I must be a confused guy, to understand Anti-Matter, without underanding what a matter is. Physicists define matter as something that has mass and comes in different forms: solid, liquid, gaseous. So, anti-matter is supposed to be the opposite of that. What could that be then !!!!
To define Antimatter, you'll have to deal with Paticle Physics. It says, everything in the Universe, has opposites just like Protons and Electrons. For every particle in nature, there is an anti particle - made of antimatter, with identical mass and spin, but with opposite electric charge, baryon number, strangeness, lepton number etc.
Antimatter was predicted by Dirac, based on strange "negative energy" solutions to his equation for an electron.
As per CERN - an European Scientific Research Lab, and as per my reading of Angels and Demons, When Matter and Anti-matter collides, there is a big-bang.
In scientific terms they call it Anhiliation - Matter and Antimatter Anhiliation.
So, the universe should have resulted in such a powerful collision of Matter and Antimatter. This supports our Big-Bang theory.
Phew ! So, many things are yet to be discovered. Still we worry about naming Tamil movies in English !! Damn !