Watch: The 5 biggest scientific mysteries, according to Neil deGrasse Tyson

Tyson chats astrophysics and alien intelligence with Chris Hayes

Published June 1, 2014 2:18PM (EDT)

  (Screenshot, MSNBC)
(Screenshot, MSNBC)

With barely restrained joy, astrophysicist and Cosmos host Neil deGrasse Tyson and MSNBC host Chris Hayes sat down for a wide-ranging discussion of the universe's biggest mysteries.

In the segment that aired Friday night, Tyson, in gracious deference to our love of lists, ranked the top five "profound areas of scientific ignorance" in his field that he's most excited about us solving. They are, as follows:

1. Dark energy, that "mysterious pressure in the vacuum of space" that's forcing the universe to expand. Quoth Tyson: "I want to know what that is"

2. Dark matter:"Basically 85 percent of all the gravity we measure in the universe has a source about which we know nothing."

3. What was around before the Big Bang, during what Tyson calls "negative time"?

4. How we went from organic molecules to self-replicating life. "That's a transition that we're challenged to accomplish in a laboratory," Tyson explained, "but Earth had no problem accomplishing this -- Earth did it early, and did it well." Added Hayes, "Nailed it."

5. The big question: whether we're alone in the universe.

To that last point: in other segments of the interview, to air next week, Hayes promised that Tyson would respond to climate deniers and creationists, specifically the outrage they've expressed at Cosmos' (reasoned, accurate) representation of science. But Tyson may have provided a clue to how he feels about all that in his riff on the idea of extraterrestrial intelligence. "My great fear is that we’ve in fact been visited by intelligent aliens,” he told Hayes. “But they chose not to make contact, on the conclusion that there’s no sign of intelligent life on Earth."

Watch the entire conversation below:

By Lindsay Abrams

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Aliens Chris Hayes Climate Deniers Creationists Dark Matter Msnbc Neil Degrasse Tyson Video