Krista Tippett, host: Theoretical physicist Lisa Randall started out seeking answers to questions in Standard Model physics and ventured into pondering extra-dimensional worlds. Now she’s moved into illuminating what she calls “the astounding interconnectedness” between fields which have previously operated more autonomously — astronomy, biology, paleontology. She’s pursuing a theory that dark matter might have created the cosmic event that led to the extinction of the dinosaurs and hence, humanity’s rise as a species. We explore what she’s discovering, as well as the human questions and takeaways her work throws into relief.

[music: “Seven League Boots” by Zoe Keating]

Lisa Randall: It’s OK to be aware of our limitations as human beings, that these are things that make it harder. It doesn’t make it impossible. And that’s the beauty of science, is that we can go beyond these prejudices, if you like, these intuitions that we have built on our ordinary, everyday experience that allows us to think about things that seem obviously wrong. They’re not obviously wrong, they’re just not obvious to us.

[music: “Seven League Boots” by Zoe Keating]

Ms. Tippett: I’m Krista Tippett, and this is On Being.

[music: “Seven League Boots” by Zoe Keating]

Ms. Tippett: Lisa Randall is the author of bestselling books for non-scientists, and she is the Frank B. Baird, Jr. Professor of Science at Harvard University. I spoke with her in 2015.

Ms. Tippett: It was interesting for me to read that you grew up in Queens and that you’ve said that as a young girl, you were more entranced with books like Alice in Wonderland than the scientific books you came across.

Ms. Randall: I actually don’t think I came across that many scientific books as a kid. Basically, I went to the library and read what I could. I just enjoyed reading. I liked the sense of adventure and play. But yeah, I can’t say that I’m really one of those people that said I really wanted to understand the stars. We didn’t actually see that many stars where I was. I think it was later on that I really came to appreciate nature more, really starting, probably, in graduate school, when I started hiking and exercising more.

Ms. Tippett: I have to say, looking at the website at Harvard — it’s The Center for the Fundamental Laws of Nature, the High Energy Theory Group. [laughs]

Ms. Randall: So I am totally not responsible for that name, which I find really arrogant and obnoxious. And I don’t think we’re responsible for the fundamental laws of nature. I think we’re responsible for the laws of nature that we can understand.

Ms. Tippett: Yeah — it is very lofty.

Ms. Randall: It’s not just lofty, it’s misleading. I think it’s misleading, because I think it gives this nature of science as ‘”We have this starting point, and then we derive everything.” But really, that’s not how it works. We try to find the starting point; we conjecture some theories. But we also try to work backwards, seeing what we observe and trying to see how those pieces fit together. So it’s really a push and pull. It’s not just one.

Ms. Tippett: That’s such an interesting way to state it. Here’s something you wrote: “Our world is rich — so rich that two of the most important questions particle physicists ask are: Why this richness? How is all the matter that I see related?” And I just wanted to ask you to explain what you’re describing there. What does “richness” mean in the context of what you do — in that sentence?

Ms. Randall: Well, I think part of what I’m referring to is simply the fact that we really don’t know how to explain why certain particles are essential to the world we live in. We know, for example, that nuclei have what we call up and down quarks inside them. But there are heavier versions. What role do they play? We know there are electrons, but there are heavier versions of the electron known as the muon and the tau. So there’s particles beyond what seem essential to nature or us or life, and we don’t really understand why they’re there. There doesn’t necessarily have to be a reason, but we’d like to see, is it somehow essential to getting us to this point in the world? So that’s part of what I’m referring to there.

Ms. Tippett: So richness is just that variety of particles and qualities that’s known and unknown.

Ms. Randall: I mean there is, of course, also the richness of how the pieces fit together, which is the wonderful stuff that we observe in the world. And we can see how that fits together and then how that came about and try to understand that with science, over time. So it’s kind of twofold. It’s sort of the richness at the fundamental level, but it’s also the richness of the complexity that derives from that, those simple ingredients.

Ms. Tippett: And it seems that the period in which you have been a scientist, these last few decades — when did you get your Ph.D.?

Ms. Randall: [laughs] I hate having to answer that, because it gives away my age. But I got my Ph.D. in ’87. But I will remind you that I took three years as my undergraduate and four years as a graduate student.

Ms. Tippett: [laughs] All right, all right. But what I’m getting at is just how it’s a short — let’s just call it a very short period of time. You’re young. It’s a handful of decades. But the scientific understanding of that richness that you were just describing, even in this period, has been so revolutionary.

Ms. Randall: It’s true, it’s been a very exciting time to be a physicist. I kind of joke that I’ve kind of lived in the optimal time. I mean I think some guys might say they would have liked to have been around earlier, but I think I’m at a very good time, because not only is science exciting, but it’s also a time that allows you to be a woman physicist a little more easily. So I feel like I live in the optimal time for me being a physicist.

But I think, also — in terms of physics, I think the last century has just seen amazing developments. I mean cosmology wasn’t truly a science until the last century, until Einstein developed his theory of general relativity, and observations improved to the point that we could actually see what’s going on and make predictions. Particle physics really only developed — nuclear physics — all the physics I worked on is a product of, basically, the last century.

Ms. Tippett: It just occurred to me — I’m kind of embarrassed to ask this question, because I feel like I should understand it. But I feel like the word — the language of cosmology and physics gets interchanged, at least in non-science circles. I mean how do you distinguish between those things?

Ms. Randall: So the other thing that gets confused is astronomy, so let me try to distinguish all of them. So physics I think of as the fundamental laws of nature. So for me, physics is elementary particle physics, but there’s all sorts of physics, which are sort of the rules by which things work. Cosmology is a specific science. It has to do with how the universe itself evolved. It has to do with the Big Bang theory, the theory of cosmological inflation, all of which I talk about in my latest book. But it has to do with just how things evolved to where they are today. Astronomy is more, in a sense, looking at stars and looking at the actual objects, how they develop, putting together. So what I like to think is, physicists are looking for sort of fundamental ingredients, astronomers are putting them together in a particular way to describe what we see today, and cosmology tells you how we got to this point. And of course, they all intertwine. They’re not completely disconnected. But someone will usually identify as an astronomer or a cosmologist or a physicist.

Ms. Tippett: That’s really helpful. Thank you.

Ms. Randall: Good that you asked.

Ms. Tippett: Well, I just suddenly realized that…

Ms. Randall: I always get mislabeled, actually, so it’s pretty funny.

Ms. Tippett: Yeah, so — well, let’s just leap in. Let’s just go to dark matter. And this book you’ve written this year also has this wonderful title: Dark Matter and the Dinosaurs.

Ms. Randall: Thank you.

Ms. Tippett: And let’s do some definition of terms, up front. I mean dark matter is, we now believe, perhaps 85 percent of the matter in the universe. Just start there. How would you talk about…

Ms. Randall: So people get very disturbed about the idea of dark matter. They say, “How could there be all this matter that we don’t see?” But there’s a lot of stuff that we don’t see. If the history of physics has taught us anything, it’s — or biology or any other field of science — it’s how much we don’t see. And dark matter, I would have — if it was up to me, I probably would have called it transparent matter. It’s matter that doesn’t interact with light. Dark stuff, as you know, absorbs light, so you see it. But dark matter, it’s matter. It interacts with gravity like the matter we know. It clumps. It’s around here, in our galaxy. But it doesn’t interact with light, so we literally don’t see it. We see its gravitational effects, but we haven’t seen other effects. We know it’s there because of the many gravitational influences of large amounts of dark matter, but an individual dark matter particle has so far eluded detection.

Ms. Tippett: I mean let’s clarify what ordinary matter — when we usually say “matter” — non-dark matter is…

Ms. Randall: So it’s the stuff that’s all around us. It’s all matter. It’s all part of what we’re made of. It’s part of Earth. It’s people. It’s the galaxy. But there’s also dark matter surrounding us, it’s just a lot less dense in our vicinity. Nonetheless, there’s billions of dark matter particles going through us all the time.

Ms. Tippett: Right now, even.

Ms. Randall: Yep, right now. But we don’t see them, and they don’t interact with us. We don’t feel them. We don’t smell them. They don’t interact with our senses. People are trying to devise very clever ways to look for very subtle, small effects, but so far as we