Lisa Randall: Dark Matter, Theoretical Physics, and Extinction Events

The following is a conversation with Lisa Randall, a theoretical physicist and cosmologist at Harvard. Her work involves improving our understanding of particle physics, supersymmetry, baryogenesis, cosmological inflation, and dark matter. This is the Lex Friedman podcast. To support it, please check out our sponsors in the description. Now, dear friends, here's Lisa Randall.

One of the things you work on and write about is dark matter. We can't see it, but there's a lot of it in the universe. You also end one of your books with a Beatles song quote, "'Got to be good-looking because he's so hard to see." What is dark matter? How should we think about it given that we can't see it? How should we visualize it in our mind's eye? I think one of the really important things that physics teaches you is just our limitations, but also our abilities. The fact that we can deduce the existence of something that we don't directly see is really a tribute to people that we can do that. It's also something that tells you, you can't overly rely on your direct senses. If you just relied on just what you see directly, you would miss so much of what's happening in the world.

Given the complexity, all cosmological scales involved here that led to the extinction of the dinosaurs, when you look out at the future of earth, do you worry about future extinction events? I do think that we might be in the middle of an extinction right now if you define it by the number of species that are getting killed off. It's subtle, but it's a complex system. The way things respond to events is sometimes things evolve, sometimes animals just move to another place. The way we've developed the earth, it's very hard for species just to move somewhere else.

Maybe let's zoom out and look at the standard model of particle physics. How does dark matter fit into it? First of all, what is it? Can you explain what the standard model is? The standard model of particle physics is basically it tells us about nature's most basic elements and their interactions. It's the substructure as far as we understand it. If you look at atoms, we know they have nuclei and electrons, nuclei have protons and neutrons in them, protons and neutrons have particles called quarks that are held together by something called the strong force.

Speaking of mathematicians, what do you is the difference, you've had a bit of foot in both, between physics and mathematics in the way it helps us understand the world? To be frank, there's a lot more overlap in physics and math. I think that has been... Maybe not more, but there's certainly a lot. I think, again, the kinds of questions you're asking are usually different. Mathematicians like the structure itself, physicists are trying to concentrate on, to some extent, on the consequences for the world. But there is a lot of overlap.