Science Buddies: "Ask an Expert"

I have repeatedly been told that there was a "slight preponderance" of matter over antimatter after the big bang. This has always bothered me as I cannot see why that should be the case. Can we say we know, (if so, how), that, random example, the Coma cluster of galaxies does not glow as a result of antiHydrogen fusing to antiHelium? Silly example, but I'm sure you understand my thought process here.

The Science Buddies "Ask the Expert" forum is for students in grades K-12 who are doing science projects.

There are other websites where your questions could be discussed. Thank you!

I know. They didn't know either.