Specifically I'd like to know about dark energy. How do we know it's 74% of the universe? I'm really looking for a specific explanation/derivation. I've searched a few places and all I've found so far has been people who say "due to Friedmann's equations" or "the WMAP measurements show that" and then there's just some hand waving and they tell you the numbers. I'm having trouble finding the complete explanation/derivation. It anyone has a link that would point me in the right direction that would be great, or just someone explaining directly right here. Thanks in advance.