“I think if I had to choose, I would rather have gravity instead of zero gravity. It’s fun for a while, but I’d rather live on Earth.” –Kevin A. Ford
By now, you’ve probably had a lot of opportunities to think about what holds our Universe together: the incredible force of gravitation. Although it’s the weakest known force in the Universe, there seems to be no limit to how much mass you can collect in one place. And so on the largest scales — like solar systems, stars and galaxies — it seems to be the only force that matters.
Yet the matter that we see and know of can simply not account for the gravitational force that we see, from its effects on the galaxy to the formation of rocky planets with heavy elements like our own. What’s going on, then?