>> thank you. martha: so what is dark matter and why do we care if we figure out what it is? >> dark matter nobody knows. that's why it is cool. it's actually probably flying through this room at this very moment. flying through our body but just passing in between spaces in@toms, not even hitting us. it is this big mystery. we think it makes up 25% of the universe but we really don't know what it is. scientists think this is one of the most fundamental mysteries of our universe and they want to get to the bottom of it. martha: what is this particle, this $2 billion particle detector? it detected something as my unscientific mind has gleanedded might be bounces off of dark matter. >> what it detected are anti-matter particles called possy trons. they think that positrons are bump into each other that create electrons and positrons, these