Martin Rees: Black Holes, Alien Life, Dark Matter, and the Big Bang | Lex Fridman Podcast #305

... there's no reason to think that the ocean ends just beyond your horizon. And likewise, there's no reason to think that the aftermath of our big bang, um, ends just at the bound of what we can see. Indeed, there are quite strong arguments, um, that it probably goes on about 100 times further. And it may even go on so much further that, uh, all combinatorials are replicated and, uh, there's another set of people like us sitting in a, in a room like this.

The following is a conversation with Lord Martin Rees, emeritus professor of cosmology and astrophysics at Cambridge University and co-founder of The Center For The Study of Existential Risk. This is the Lex Fridman podcast. To support it, please check out our sponsors in the description and now, dear friends, here's Martin Rees. In your 2020 Scientific American article, you write that, quote, "Today, we know that the universe is far bigger and stranger than anyone suspected." So what do you think are the strangest, maybe the most beautiful or maybe even the most terrifying things lurking out there in the cosmos?

Well, of course, we're still groping for any detailed understanding of the remote parts of the universe, but of course, what we've learnt in the last few decades is really two things. First, we've understood that the universe had an origin about 13.8 billion years ago in a so-called big bang or hot dense state whose very beginnings are still shrouded in mystery. And also, we've learned more about the extreme things in it, uh, black holes, neutron stars, explosions of various kinds, and one of the most potentially exciting discoveries in the last 20 years, mainly the last 10, has been the realization that most of the stars in the sky are orbited by retinues of planets just as the sun is orbited by the Earth and the other familiar planets. And this, of course, makes the night sky far more interesting. What you see up there aren't just points of light, but they're planetary systems and that raises a question, could there be life out there? And so that is an exciting problem for the 21st century.

So when you see all those lights out there, you immediately imagine all the planetary worlds that are around them and they potentially have all kinds of different lives, living organisms, life forms or different histories.

Well, that, that we don't know at all. We know that these planets are there. We know that they have masses and, um, orbits rather like the planets of our solar system, but we don't know at all if there's any life on any of them. I mean, it's entirely logically possible that life is unique to this Earth, doesn't exist anywhere. On the other hand, uh, it could be that the origin of life is something which happens routinely given conditions like the young Earth. In which case, there could be literally billions of places in our galaxy where some sort of biosphere has evolved. And, uh, settling, um, where the truth lies between those two extremes is a challenge for the coming decades.