The Big Bang theory has been extremely successful in describing the history and evolution of the Universe, and new experiments and observations continue to confirm the basic predictions of this theory. But we do not yet know the answer to the question
The evidence for dark matter and dark energy has rewritten this question, redirected our efforts to address it — and strengthened the motivation for finding an answer. Dark matter and dark energy cannot be explained by our current model of fundamental physics; deciphering these mysterious substances will require a leap into a new realm of understanding, a theoretical upheaval that will rival the changes brought about by quantum mechanics and general relativity.
Einstein's Telescope: The Hunt for Dark Matter and Dark Energy in the Universe (2009), Epilogue : Dark Matter and Dark Energy: Keys to the Next Revoution, p. 267
Neutrinos are fundamental subatomic particles produced in nuclear reactions, like those in the sun. We always talk about the fact that we can’t see neutrinos or dark matter and that basically they’re invisible, but if you think about it from the other side, we’re also invisible to them.
Nothing in nature or the cosmos is ever completely still — as I write this, several wild Mallards have returned to the Museum courtyard and are creating a frantic spectacle of water and wings as they dive and attack in their annual spring ritual. Further from home, a supermassive black hole at the center of a galaxy 56 million light years from Earth has recently been observed to be spinning at close to the speed of light.
"Letter from the director", Explore magazine of the Cleveland Museum of Natural History (Spring 2013), p. 4