But suppose there was an antimatter universe that had lots of anti-hydrogen and anti-helium after its big bang, just as our early universe had lots of hydrogen and helium. It would seem reasonable that these could fuse to heavier antimatter elements in the cores of antimatter stars, and this could produce antimatter planets and perhaps even antimatter life. What would these creatures see when they look up into their night sky?
In this case we know it would look much like our own night sky. Recently we’ve been able to produce anti-hydrogen, and we have looked at the type of light it produces. We found that anti-hydrogen produces the same kind of light as regular hydrogen. So an antimatter Sun would emit the same light as our Sun. Light would reflect off an antimatter moon just as it does our Moon, and our antimatter cousins would see a sky filled with stars, nebulae and planets, just like we do.