Dark energy and dark matter ... Can't find it, and can only very marginally prove it even exists ... but nevertheless it seems to make up the vast majority of the universe. Until today I'd read that all visible matter and energy in the universe made up something like 13% of the total. It seems that this was an over-estimate. We're now down to 4%. What a stunning thought ... most of our universe is missing. Until 11 years ago, we didn't even suspect this. What a humbling thought ... man is in his arrogance once thought he was on a verge of understanding everything. Now we realize that we've only just learned enough to discover how ignorant we really are. I remember reading something Heinlein once wrote, but I can't find it to quote it exactly. Basically it was the idea that our ignorance is a cloud on the horizon. Back in 1900 or so we didn't know much about the cloud because it was away on the horizon ... but it looked pretty small. As we learned more (getting closer to the cloud) it gradually got bigger and bigger until finally the bank of clouds stretches as far as we can see to left and right. We've only just reached the point of knowing how little we know.