the source of dark energy Like rest masses attract - so presumably unlike rest masses would repel, if rest masses were similar to charges. But where are any gravitationally repulsive rest masses in our universe? Antimatter is missing too. Nobody knows what dark energy is. So, could dark energy be gravitationally repulsive antimatter? There is far more rest mass equivalent(E=mc^2) in dark energy than could come from an amount of antimatter equal to the amount of baryonic matter in the universe (we would expect a 50/50 ratio). But if much more baryonic matter and antimatter existed in the early universe and dark energy had as its source baryonic matter and antimatter, then it could well be made from them.