Anti-Matter

At the Big Bang equal amounts of Matter and Anti-Matter were created.  When they meet they destroy each other, but Anti-Matter decays faster. 

The matter we see in the universe today is just a tiny fraction of two vast seas of matter and anti-matter.  They would have completely destroyed one another were it not for the tiny imbalance Joanne (Hewitt) and her colleagues found between the B and Anti-B Mesons.