By the way, there's something I've been wondering about for a long time.
I read somewhere that there are no antiphotons and antimatter emits light just the same as normal matter.
So, I assume that there's no way to tell whether a photon was emitted by antimatter or by matter.<p>Therefore, how do we know distant galaxies aren't made of antimatter ?<p>Maybe there's an obvious answer, but as far as I know, the only thing we can know about these galaxies, we know because of the radiation they emit.