[RADIOLAB INTRO]

LULU MILLER: What's another word for a male frog that has some children?

LATIF NASSER: What? What's another word for a male frog that has children?

LULU: Mm-hmm.

ALIE WARD: A—a daddywog. A tad—dadpole.

LULU: There you go!

ALIE WARD: Yes! [claps]

LATIF: [laughs]

LULU: Okay, sorry.

ALIE WARD: I feel cazh. I already feel like we're at a—like, a sleepover instead of, like, at an official recording.

LATIF: [laughs]

LULU: Hey, I'm Lulu.

LATIF: I'm Latif.

LULU: This is Radiolab.

LATIF: And this week, we actually—we brought in a third host, as if there weren't enough of us. A host we are quite a big fan of.

LATIF: Alie, your show is awesome.

LULU: It's so great.

ALIE WARD: Thank you!

LATIF: Her name is Alie Ward. I actually realized during our conversation with her that she is my neighbor. But we brought her in because we wanted her to tell you about her podcast.

ALIE WARD: So let the games begin. Ask me anything.

LULU: What is the name of your show, and how would you describe it?

ALIE WARD: So Ologies is a comedy-ish science podcast where we explore a different ology every episode. So it might be geology one week and then philematology the next, which is the study of kissing. So ...

LULU: Alie has taken on so many ologies.

ALIE WARD: Testudinology, which comes from the Latin testudo for "tortoise."

LULU: Enigmatology.

ALIE WARD: Hagfish!

LULU: Hagfishology.

LULU: Would it be raccoonology, or would it be ...?

ALIE WARD: [laughs] No.

LULU: Meteorology, apiaryology.

LATIF: Chickenology.

LULU: Melaninology.

LATIF: Quantumontology?

LULU: Chronobiology.

ALIE WARD: Carnivorous phytobiology.

LULU: Flesh-eating plants.

LATIF: Your urology episode was one of my favorites, and I did not think I would—like, I very reluctantly clicked on that.

ALIE WARD: Thank you.

LATIF: And we brought Alie on because her show is kind of like a kindred spirit to our show, but also, it's very different at the same time. Like, for our show we talk to a bunch of scientists, but it's usually in the context of a story or a big idea we're interested in, and then we try to make it all add up to something. Alie does not do that part. She just will be like, "Oh, this scientist is interesting," and then they will sit down and they will just go to town.

LATIF: And actually, one of the things I love about your show is like—like, your "what matters" is totally different than our "what matters." Like, what does it matter when it's a random thing that—that it seems like maybe only this one scientist you're talking to cares about?

ALIE WARD: I love this question, and I completely get it. So here's the thing: science is everywhere. Science is in how you steam broccoli, science is in how you park your car, science is in who you fall in love with, science is why you sweat when you get a text message that freaks you out. Like, it's not just about diagrams and textbooks.

ALIE WARD: And I think it's also interesting that a lot of people who are not scientists think that scientists are jerks and pedantic and are there with, like, a huge book of facts to tell them that they're wrong about things. And I wanted to show that, like, scientists are curious little weirdos who found their niche in whatever made them passionate, and they make mistakes, and they—they have hypotheses that end up being wrong, and they're figuring it out too. And so humanizing scientists I feel like galvanizes people to care a little bit more every time they see a research paper and they think, "I wonder why this person studied this?" or, "I wonder how long it took to get this published?" And so the civic duties that we have to protect things and care about things become easier for people when they have a little bit more context.

LATIF: But, like, okay, so like—like, how do you know how to—that people will stay with you for all of these—for your to go down—like, how far they'll follow you before they'll just be like, "Alie just totally lost it." Like, this is ...

LULU: [laughs] Lost the plot?

LATIF: Yeah, lost the plot.

ALIE WARD: Yeah. I mean, it's really kind of more of—like a lightning bug kind of darting around. It's just following the light.

LATIF: So for the rest of this episode of our show, we're gonna follow Alie into an episode of her show as she follows the light bouncing around like a little lightning bug like she does into the dark.

ALIE WARD: Oh, scotohylology. Scoto means dark, hylology means matter.

LATIF: We're gonna play her episode on dark matter for you.

ALIE WARD: I actually—that was a rare one where I worked with the ologist to be like, "There needs to be a word for this. How do you feel about this?" And he loved it.

LULU: You coined a term?

ALIE WARD: I coined it.

LATIF: It's one of the very few conversations I've heard that actually makes dark matter makes sense to me.

LULU: And—and even feel like it matters.

LATIF: Yeah.

LATIF: So we're gonna turn it over now to Alie with UC-Riverside theoretical particle physicist and dark matter expert Flip Tanedo.

LULU: And just a quick heads up, the lovely Alie Ward is not afraid to ...

LATIF: Mince words?

LULU: Dirty her tongue? That's not an expression. She's not afraid to swear, so they—there are few swear words ahead. Here we go.

ALIE WARD: Did you set out to become a theoretical physicist? How does one land in, like, what I feel like is the hardest field possible?

FLIP TANEDO: [laughs] All right, here is my origin story. I wanted to be an author.

ALIE WARD: Really?

FLIP TANEDO: I had no idea why, but I was very passionate about writing. The idea that one can have a voice.

ALIE WARD: Mm-hmm.

FLIP TANEDO: And so growing up, I was a huge fan of LeVar Burton's because of Reading Rainbow.

ALIE WARD: Oh, love, love, love, love, love. Yeah.

FLIP TANEDO: Reading Rainbow, amazing.

[ARCHIVE CLIP, Reading Rainbow: But you don't have to take my word for it.]

FLIP TANEDO: So I would watch Reading Rainbow, and at some point in the back of my mind, I realized this person who does Reading Rainbow is also on this TV show Star Trek.

ALIE WARD: Mm-hmm.

FLIP TANEDO: And in high school, I started watching Star Trek a little bit. It was still on at the time. I picked up the book The Physics of Star Trek by Lawrence Krauss. And this was a really fun ride because it was the first time I thought about a scientific subject as something where there are open questions, and these open questions are fun and creative and exciting. And anytime that I lost track of it being exciting I just watched LeVar Burton as Geordi La Forge.

ALIE WARD: Uh-huh.

FLIP TANEDO: As the chief engineer.

ALIE WARD: I know it well. Oh my gosh, my sister and I used to watch The Next Generation as well.

FLIP TANEDO: Yeah, it was the best.

ALIE WARD: Yeah.

[ARCHIVE CLIP, Star Trek: The Next Generation: You can't change the gravitational constant of the universe, but if we wrap a low-level warp field around that moon, we could reduce its gravitational constant, make it lighter so we can push it.]

FLIP TANEDO: So I think that's—that's what got me into this idea that hey, these black holes in the show, these are real.

ALIE WARD: Mm-hmm.

FLIP TANEDO: We should understand these things. There are fundamental questions that are not only abstract and things you would find in textbooks, but they're fun ideas. And—and it was the creative spark that was really exciting, that someone could write a science fiction piece about these actual things. And that's what got me going with physics.

ALIE WARD: Do you write still at all?

FLIP TANEDO: [laughs] I was never a great writer, and you can ask my collaborators that my—my paper writing is slow and tortuous.

ALIE WARD: [laughs]

FLIP TANEDO: But I—I would like to eventually write something as a popular book.

ALIE WARD: Oh yeah, I feel like that is in your future. But when it comes to matter and dark matter, I mean, slow it way down for baby brains like mine, but from what I understand—and the first time I ever read this was like, okay, all of the matter that we can see and touch and feel and everything makes up about 15 percent.

FLIP TANEDO: Yeah, depending on how you're counting, but yeah, it's a tiny fraction.

ALIE WARD: Like a third of that. So everything that you can see and feel and touch and smell, that's five percent of the universe's mass and energy. There's another 95 percent of pure mystery. So then what the fuck is everything else? What is it?

FLIP TANEDO: That is—yeah, that is the—the—this is the mind-blowing thing: we've known about dark matter indirectly for a hundred years.

ALIE WARD: Mm-hmm.

FLIP TANEDO: And I think it hasn't been until fairly recently that this has come to the forefront of we really ought to figure out what this stuff is.

ALIE WARD: [laughs]

FLIP TANEDO: Because as you said, we spend all of our lives learning science, art, history, everything you learn from a textbook is basically about that really tiny slice of visible normal matter.

ALIE WARD: Mm-hmm.

FLIP TANEDO: And the history of that normal matter in this universe and in this world and in our culture. But it turns out for every—let's see, what's the fraction? I think if you look at the amount of energy, so energy is a good measure for stuff.

ALIE WARD: Mm-hmm.

FLIP TANEDO: 25 percent of the universe is made of dark matter, and only five percent is made of the stuff that we are used to.

ALIE WARD: Wow!

FLIP TANEDO: And so there's five times more dark matter than ordinary stuff. And in fact, it's so much more that we look at our galaxy and we think our galaxy is huge. Our galaxy is almost everything, everything we could possibly care about.

ALIE WARD: Mm-hmm.

FLIP TANEDO: Our galaxy is only here because it is swimming in an ocean of dark matter that provides the gravitational pull to keep the galaxy there. Like, the galaxy formed because there was dark matter.

ALIE WARD: What?

FLIP TANEDO: So where we are right now with scotohylology—is that what we're doing?

ALIE WARD: Mm-hmm. Yes. Nailed it.

FLIP TANEDO: This is the fish scientist discovering for the first time that there's this thing water that we're swimming through. We should figure out what this water is.

ALIE WARD: Wow! And now the other—let's say is the other 70 percent dark energy?

FLIP TANEDO: Good. Yeah, so that is a great—I was both hoping and not hoping that you would bring that up.

ALIE WARD: [laughs]

FLIP TANEDO: So 25 percent dark matter, five percent ordinary matter. That doesn't add up to 100 percent.

ALIE WARD: Mm-hmm.

FLIP TANEDO: And so the rest is indeed dark energy. And I'm excited that I have no idea what dark matter is, and there are great things to do in that field. I have no idea what it is. Dark energy, I have no fucking idea, and I'm terrified and that's—there's a reason why I don't work on it.

ALIE WARD: [laughs]

FLIP TANEDO: It's one of those shows, right?

ALIE WARD: Yeah, of course. Very much so. Especially this topic. There's gonna be a lot of boggling, trust me. What—I mean okay, so about a hundred years ago, was that when we realized—I say "we," the royal we here—like, that something is not adding up?

FLIP TANEDO: That's right. That's right.

ALIE WARD: Yeah. When did we realize that?

FLIP TANEDO: I think this was about a hundred years ago. The first astronomical observations were—and this is what was really, really trippy, though. The origins of scotohylology ...

ALIE WARD: Mm-hmm.

FLIP TANEDO: ... were really in astronomy. And people would look at galaxies and look at how fast stars were moving in those galaxies, and just using ordinary non-fancy Newtonian physics, the type of physics that—that students groan over in high school, they figured out that these stars around—moving around these galaxies were going a little bit too fast. It's as if there was more gravity than they had accounted for just by counting stars. And I'm gonna do a great disservice to my astronomer colleagues, but for the most part, the astronomy field said, "Huh. That's curious," for—for maybe 50 years, 60 years.

ALIE WARD: Uh-huh.

FLIP TANEDO: Because there are lots of curiosities in astronomy.

ALIE WARD: Right.

FLIP TANEDO: Over the next hundred years, we had more and more mounting evidence that this additional gravity, which in the 1920s, who cares? We just didn't happen to count all the stars correctly.

ALIE WARD: Mm-hmm.

FLIP TANEDO: But now there's more and more evidence coming from more and more sophisticated measurements that not only is there more stuff, but that stuff cannot be the stuff that we are made of.

ALIE WARD: So there is stuff all around us, out-massing us and out-energying us, maybe by a factor of 20, but we can't see it. And we don't understand it. So this whole time we thought that we were a cookies and cream milkshake. We're just the Oreo bits, and we're surrounded by an invisible milkshake that can seep through us. We don't know what it is or what it does. So dark matter, it doesn't interact with light or electromagnetic forces which is why we can't see or feel it. So why do we know it's there? Fritz Zwicky first coined the term "dark matter" in 1933—more on him later—but it wasn't until this astronomer named Vera Rubin crunched some numbers and hypothesized that dark matter exerts gravity, and without that gravity galaxies would just fly apart and scatter if it all just depended on the normal matter or baryonic matter, which is the atomic stuff that we know of, like protons and neutrons and electrons. So when did she figure that out? Oh, just in 1978. We just found this out a split second ago in the universal timeline.

ALIE WARD: Get this. So Dr. Vera Rubin, she did her calculations at this observatory that didn't even have women's restrooms. There were no ladies' rooms at the observatory. She had to cut up a silhouette of a dress and paste it on one of the men's rooms. And then when she was done crafting, then she pioneered some giant theories about the existence of the universe. And she died in 2016. She was never awarded the Nobel Prize, and they unfortunately do not hand those out posthumously—which is a bummer. But you can name your dog Vera or your cat Rubin and remember Vera Rubin that way. But anyway, dark matter, it is—it's something else.

FLIP TANEDO: It cannot be the stuff that we're used to from chemistry. And then the fundamental particle physicists, the elementary particle physicists realized we've been spending the past five decades trying to categorize the elementary particles of nature. We're trying to have the most fundamental periodic table, and you're telling me that there is something that we're missing and that we definitely have to put on here?

ALIE WARD: Wow!

FLIP TANEDO: And this became a big thing. If you'll permit me an aside.

ALIE WARD: Yes.

[ARCHIVE CLIP: I was hoping you'd say that.]

FLIP TANEDO: So I'm gonna get the history a little bit jumbled, but this is the moral history. This is the way that we're gonna remember it.

ALIE WARD: Okay.

FLIP TANEDO: In the '80s and '90s, there was one big hot question in particle physics, and that question had to do with the Higgs boson. The Higgs boson that in 2013 won the Nobel Prize for its discovery. Big deal.

ALIE WARD: Mm-hmm.

FLIP TANEDO: Big fucking deal in particle physics.

ALIE WARD: [laughs] And now that's sometimes wrongly called the God particle?

FLIP TANEDO: Yes. [laughs]

ALIE WARD: Okay. Right.

FLIP TANEDO: That is the quote-unquote "God Particle."

ALIE WARD: Right.

FLIP TANEDO: And if you ask physicists in my generation, its discovery was—was more like the Satan particle, where—where we had to really do some soul-searching.

ALIE WARD: [laughs] Because?

FLIP TANEDO: Because in the '80s and '90s, we had realized there's probably a Higgs. If there's not a Higgs, things get way more interesting.

ALIE WARD: Mm-hmm.

FLIP TANEDO: But if there's a Higgs, something isn't quite right in the theory because for all the reasons that we needed to have the Higgs, if the Higgs had the mass and the properties that we needed it to have, somehow it just didn't seem right. It was far lighter in mass than it really ought to have been. So we now know it weighs about 125 times the mass of a proton, which is pretty honking for a fundamental particle.

ALIE WARD: Mm-hmm.

FLIP TANEDO: And our prediction, naïvely, if I gave that calculation to a first-year grad student they'd say it's probably way heavier than that. It's like balancing a pencil on its tip. The quantum corrections to its mass would make the Higgs heavier than it actually is.

ALIE WARD: And just some very brief background on this. So Higgs particles make up the Higgs field, which is this big cloud of bosons or particles. So matter started out zipping around like photons just unencumbered by mass, but interaction with the Higgs field is what makes matter interact with gravity and have that mass be gravitationally attracted to each other. But Higgs bosons? Very hard to find. You have to get, like, a large Hadron Collider, say. Maybe 27 kilometers under Geneva. And then you gotta race protons at each other, you gotta explode them. And then you gotta measure what's left, AKA a decay signature. And if you're looking through all those pieces and you have pieces and parts for what could have been a Higgs boson that existed for a fraction of a millisecond, then that's almost, almost proof. But for a long time, this possibility of the Higgs particle had vexed science for years. One leading scientist wanted to call it "The Goddamn particle," but his book publisher was like, "Let's go softer," and naïvely made the facepalm modification to just call it the God particle, which has been making physicists cringe for decades now. But yes, essentially, things just didn't add up.

FLIP TANEDO: And so this was a huge puzzle. It's analogous to having an ice cube sitting in an oven, and you turn the oven on and the ice cube's still there.

ALIE WARD: Wow.

FLIP TANEDO: So we called this the Hierarchy Problem, and for people like me, we write it with a capital H when we write our academic papers. It was a big deal. It seemed to be the reason why our theory of particle physics just could not be complete.

ALIE WARD: Mm-hmm. So prior to 2013, they knew something really wasn't quite right.

FLIP TANEDO: And so we had these great exotic theories. They had funny names: supersymmetry, extra dimensions, compositeness. You know, maybe—maybe the electron and its cousins are not fundamental, but are actually made of smaller things.

ALIE WARD: Oh, wow.

FLIP TANEDO: So this was the heyday in the '90s of doing particle physics. And right around that time, as we were developing these really awesome theories, people realized, hey, in order for this theory to work, meaning in order for protons not to decay too quickly, in order for the universe to actually look like the way it does, we need to tweak it a little bit. And one output is we get these new particles that stick around. They don't decay, they're just around. That's—that's kind of weird. And I imagine there's some physicist, particle physicist sitting in his office saying this. An astronomer walks by and says, "You have particles just sitting around contributing a mass? Have you heard about this—this anomaly that we have? There's more mass in these galaxies." And so particle physicists, who were—I mean, we're kind of smug.

ALIE WARD: [laughs]

FLIP TANEDO: Just said, "Oh. Yeah, okay. Good. I have discovered what your dark matter ought to be. You—in 15 years when we turn on this collider, we're going to discover what this particle is, we'll measure how heavy it is. And I will tell you exactly what's in these galaxies that you've been looking at for the past hundred years." This was the promise.

ALIE WARD: Yeah.

FLIP TANEDO: And so particle physicists didn't even care about the dark matter because that was the output of this elegant theory that solved the capital H Hierarchy Problem.

ALIE WARD: And just a side note: so the capital S Standard, capital M Model of particle physics involves this uniform framework for understanding electromagnetic and weak and strong interactions. And the Hierarchy Problem is the difference between the way a weak force, which is a force that allows protons to become neutrons and then back and forth, vice versa, so that weak force is actually not weak at all. It's 10²⁴th times stronger than gravity, but only at really short distances. So this was the big strong weak elephant in the physics room.

FLIP TANEDO: So that's how I was trained as a grad student.

ALIE WARD: Yeah.

FLIP TANEDO: And the year that I graduated was 2013. I had written some papers on extra dimensions and all of these exotic new things that we would predict that we would see at the LHC, and by the time that I turned in my thesis, it was pretty clear that none of those things would be discovered.

ALIE WARD: Wow!

FLIP TANEDO: We had discovered the most basic, the most boring version of the Higgs boson, and none of the things that we predicted for the—the overarching theory that would explain why it was there. And then we got stuck.

ALIE WARD: Oh.

[ARCHIVE CLIP: Bummer. What a mindbender, huh?]

FLIP TANEDO: And I think this is where there's been a bit of a renaissance in the theory of dark matter, because on the one hand, the smug particle theorists like me, who had assumed that we—of course dark matter is this thing, all of our best theories predict this thing, well, that's out the window, but dark matter is still out there. And meanwhile, actually all of these theories that we spent our time building and cutting our teeth understanding, maybe the simplest versions of those guys are out the window too. So what—what are we working on? So several of us are still working on understanding the Higgs, but armed with all of these new fancy techniques for building theories, several of us went on to think about dark matter. Because now we can look at this problem with fresh eyes, without the prejudice of well, there's this more important problem that has this more important solution, and this is just the byproduct of that thing. Now we've been thinking more open-endedly about what dark matter could be, not just what we expect it to be.

LULU: More on dark matter from Flip Tanedo after a quick break.

***

LULU: Lulu.

LATIF: Latif.

LULU: Radiolab. We are back with Alie Ward on scotohylology ...

LATIF: ... AKA the study of dark matter ...

LULU: ... with theoretical particle physicist Flip Tanedo. Here's Alie.

ALIE WARD: What about the name dark matter and dark energy? Because it's invisible at best, right?

FT Absolutely.

ALIE WARD: Who decided that it would be called dark? Who decided that it would have a spooky name?

FLIP TANEDO: That is a great question. I think it was Zwicky, who was a famously cantankerous physicist in the early part of the 20th century.

ALIE WARD: So yes, this was 1933, with Cal Tech's Fritz Zwicky. And when you hear the words "famously cantankerous," I know you want the story time. And among a lot of different legends and slander and feuds and jealousy and what sounds like maybe a touch of old-timey verbal abuse, if his enemy's stories were to be believed, Zwicky would allegedly call his colleagues scatterbrains and spherical bastards. Spherical, because, quote, "They are bastards every way I look at them." Ooh! Messy. I love it. But a 2008 article in Discover Magazine features testimony from Zwicky's daughter Barbarina that Dr. Fritz was just so brilliant that he had a lot of haters. But he was the one ...

FLIP TANEDO: ... who coined the term "dark matter." And what he meant was that it doesn't interact with light.

ALIE WARD: Ah!

FLIP TANEDO: Yeah. So usually we think things that are dark don't interact with light, but actually probably there's some junior high student out there who will say, "No, no, no. Things that are dark absorb light. They're actually maximally interacting with light."

ALIE WARD: [laughs]

FLIP TANEDO: If you're an astronomer, "dark" means you don't see any photons from it.

ALIE WARD: Mm-hmm.

FLIP TANEDO: So I think that's why they used the word "dark." And to the best of my knowledge, I think dark energy, which was discovered a little bit later as a big question mark, they latched onto the branding that we'd developed, and they used the word "dark" to mean, just like dark matter, we don't know what this is, but at least dark matter we had the idea that this was stuff, these were particles. I'm 99.9 percent sure dark matter is at least one particle. Dark energy definitely behaves differently, and it's a much weirder thing.

ALIE WARD: Do you drive around in traffic and think about this stuff? Like, can you ever escape theorizing about this?

FLIP TANEDO: Oh, that is a great question! I think the imposter syndrome in me says, "Yeah, I escape it way too much." But traffic in LA, as you know, is not a great place to have happy thoughts. But I often find myself thinking about physics in the swimming pool.

ALIE WARD: Really?

FLIP TANEDO: And so for example there's this idea of we are fish in an ocean of dark matter. That was something that I was thinking about while swimming. And I guess being in a mathematical discipline, you're sharpening your equipment. Like, having the finest equipment is really having a clear mind, and I can sit at my desk and I can do a calculation, I can write a paper, but the creative spark is something that usually happens outside of those environments. So walking around, or having tea on my patio, that's—that's where the magic happens.

ALIE WARD: And be honest with me. Without having to name names, how many astrophysicists out there think that dark matter might be ghosts? What if dark matter is ghosts? What if dark energy is ghosts? What if it's all ghosts? What if we're swimming in ghosts?

FLIP TANEDO: [laughs] There is a famous quote from Nima Arkani-Hamed before the LHC turned on, and the quote was something along the lines of, "We might turn it on and dragons might pop out. We have no idea what's gonna happen."

ALIE WARD: [laughs] So in a March, 2008, New York Times article, this particle theorist who was at the Institute for Advanced Study in Princeton told the paper that there was some probability of almost anything happening. Even a minuscule chance that, quote, "The Large Hadron Collider might make dragons that might eat us up." Maybe he was just ahead of the curve in predicting the 2011 premiere of Game of Thrones. But either way, people were rightly pumped.

FLIP TANEDO: And that kind of encapsulates a lot of the excitement. There is something to be said about, maybe dark matter is something much more exciting than particles. And there are theories where the dark matters—plural—could form dark atoms. Just like you have protons and electrons, maybe you have something like a dark proton and a dark electron that we can't see, but they can see each other. And those form dark atoms, and then it's not hard to imagine, well, those dark atoms could have dark chemistry, that dark chemistry could form dark life, that dark life could maybe—maybe there's an entire sentient civilization living in our dark matter halo where our galaxy is sitting, and we just don't realize it. But because there is five times more of them than there is us, we are the ghosts. We are the weird thing.

ALIE WARD: Oh, wow! Oh my gosh! You're trying to make sense of dark matter using a field of math that applies to everything else.

FLIP TANEDO: Yeah.

ALIE WARD: Is there a possibility that there's a dark math? That's there's just a completely different way of trying to quantify everything?

FLIP TANEDO: Oh! Oh boy. Okay. That is one perhaps for the philosophy department. And I say that very carefully because I think usually when a physicist says, "That's for the philosophy department," that—that's probably condescending. That's probably dismissive. That's how we say, "I don't want to think about that." The assumption is math is logical rigor, and so that just has to be true. And I don't even know how to think about a different reality, a different universe that has different laws of math. I can imagine a different universe where the fundamental constants are a little bit different. Maybe there are more particles, fewer particles, but I don't know how to think about one where math is different.

ALIE WARD: Is there a myth that you would love to bust about dark matter? Like, what is one thing that the public thinks they know about it that they don't? Other than that it's ghosts.

FLIP TANEDO: [laughs] Oh, that's great. That is a great question. I'll start with a basic one. It's not anti-matter.

ALIE WARD: Okay.

FLIP TANEDO: It's not anti-matter. It's probably also not black holes.

ALIE WARD: Okay.

FLIP TANEDO: So these are the other two, like, exotic things that you learn from Star Trek.

ALIE WARD: Yeah.

FLIP TANEDO: So it's not anti-matter, because if we're swimming in a sea of dark matter, and if the dark matter were anti-matter, it would keep annihilating with ordinary matter and producing light. So the fact that —I was gonna say, we're not a glow stick in the universe, but really the fact that our galaxy isn't just being burnt up by the anti-matter, that means dark matter is not anti-matter.

ALIE WARD: Nice.

FLIP TANEDO: Until fairly recently, we would say it's not black holes because black holes are a totally different thing, but there have been some thoughts recently that there might be little tiny black holes that were formed in the early universe that would behave like dark matter.

ALIE WARD: How tiny are we talking?

FLIP TANEDO: That's a good—there's a range of sizes.

ALIE WARD: Mm-hmm.

FLIP TANEDO: But the story of little black holes is funny. For a long time, people were worried that turning on the LHC would produce lots of little black holes that would eat the Earth.

[ARCHIVE CLIP: Sounds like fun.]

FLIP TANEDO: But we were pretty sure that the little black holes evaporate and would be relatively harmless. Little black holes might be little particles.

ALIE WARD: And do you think that those could be just on Earth in just little, you know, pockets here and there?

FLIP TANEDO: Chances are no. I would bet no. But it is a theoretical possibility. It's attached to a whole bunch of other weird things. I think to make it work out gravitationally, you'd need to have extra dimensions, and maybe a few extra dimensions. But it was a fun thing to think about 10 years ago.

ALIE WARD: Do you think that dark matter could be extra dimensions?

FLIP TANEDO: That is a great question. That is what I spent my summer vacation thinking about.

ALIE WARD: [laughs]

FLIP TANEDO: So extra dimensions are a really funny quirk in the history of theoretical physics. I think the modern way of thinking about this is the people who work on extra dimensions don't necessarily literally believe in, "If I could just step in the right way, I'm gonna be in some parallel universe." But in the mathematics, one realizes that if I can write a theory in three-dimensional space plus one-dimensional time, I could write a theory in four dimensions of space plus one dimension of time, or in five dimensions of space and one dimension of time. No problem, right? It's just—it's another number that you add onto your mathematical expressions. And so people, it was easy to play with, and in the 1990s, one of the huge revolutions in theoretical physics was this observation that particular types of theories with extra dimensions end up giving mathematically equivalent predictions—when you ask the right question—to a type of quantum theory that is really hard to calculate. This is something called a duality in physics. And it meant that I could calculate something in my wonky theory of extra dimensions, and that calculation would actually mean something in an ordinary theory—ordinary meaning three dimensions of space, one dimension of time—that is highly quantum mechanical, but a perfectly plausible theory. And it was a type of theory that we really didn't know how to deal with until we had tools like this.

ALIE WARD: Tools like the Large Hadron Collider.

FLIP TANEDO: And so one of the fun things to play with is we have this really powerful machine to make predictions where we couldn't make predictions 20 years ago. Maybe we can describe cool theories of dark matter that one, could explain why we haven't discovered dark matter, and two, could motivate interesting different searches, because this is where we are right now, and we need to figure out what is the best way to test these different theories of dark matter?

ALIE WARD: It better happen in my lifetime. I mean, I'm sure you think the same thing, given that this is your life's work.

FLIP TANEDO: Yes. Yes, yeah. And in fact this is—for me, this is the difference between dark matter and dark energy. Both of them are things. We have no idea what they are. I certainly have no idea what they are. Dark matter, we have an experimental program, and we know enough about it that I have faith that we have a sporting chance that we will learn something deep about dark matter in my lifetime. Dark energy? I'm not even sure if we'll learn anything about it in the history of humanity.

LATIF: Hey, Latif here again. We're gonna jump ahead , because Alie asked Flip so many great questions.

ALIE WARD: What does dark matter look like in your head? Time travel: yes, no, maybe? What is the best music to listen to while researching dark matter?

LATIF: I would honestly just listen to a podcast that was only Alie asking questions. They are so great.

ALIE WARD: How much dark matter is in the room right now?

FLIP TANEDO: We actually know this.

ALIE WARD: Oh! Okay.

FLIP TANEDO: In your coffee mug you have about one gram of dark matter.

LATIF: If you want to hear all of Flip's answers, you can listen to the full episode. We'll link to it on the website. But before we go, we will leave you with this one last question and answer from Alie and Flip.

ALIE WARD: What about your favorite thing about what you do?

FLIP TANEDO: Oh, gosh! I love that on any given day, there are new things to learn, and either it's some experimental result that I won't understand, or some related field where I never had the chance to take that class as a student, but I see that there's an opportunity where dark matter might be able to do something, and then I can dig in and say, "I have an excuse to spend my time reading this textbook, or reading this recent article or talking to my colleague from a different department." That's the fun part.

ALIE WARD: That's great. I mean, I love that for the rest of my life, I'm gonna be walking around thinking about a gram of dark matter in my coffee cup and sparkly webs and maybe ghosts.

FLIP TANEDO: Maybe ghosts. [laughs]

ALIE WARD: You don't have to commit to that on the record. I just—for my own fun.

FLIP TANEDO: Well, I would add — my "Yes, and" would be, thinking about all of the dark matter scientists who are thinking about us and we're the maybe ghosts.

ALIE WARD: Oh, I love them. Thank you so much for doing this. This was a joy.

FLIP TANEDO: Thank you, Alie!

ALIE WARD: Oh my gosh. Yay!

LATIF: Thanks to Alie Ward and her team for letting us share her show with all of you. Hopefully, you'll go check it out. You can find it wherever you get podcasts, or at Ologies.com. That's O-L-O-G-I-E-S.com.

LULU: They also, by the way, make one suitable for kids where they rip out all the swears. Those are called "Smallogies." Big thanks again. This episode was produced by Pat Walters, with mixing help from Arianne Wack.

LATIF: And I don't think there are any special thanks, so I'm just gonna thank you. Thank you for listening.

LULU: New episode in your feed coming up in a couple weeks, and it is a really good one. It's an odyssey. Catch you then!

[LISTENER: Radiolab was created by Jad Abumrad, and is edited by Soren Wheeler. Lulu Miller and Latif Nasser are our co-hosts. Dylan Keefe is our director of sound design. Our staff includes: Simon Adler, Jeremy Bloom, Becca Bressler, Rachael Cusick, Ekedi Fausther-Keeys, W. Harry Fortuna, David Gebel, Maria Paz Gutiérrez, Sindhu Gnanasambandan, Matt Kielty, Annie McEwen, Alex Neason, Sarah Qari, Anna Rascouët-Paz, Sarah Sandbach, Arianne Wack, Pat Walters and Molly Webster. With help from Andrew Viñales. Our fact-checkers are Diane Kelly, Emily Krieger and Natalie Middleton.]

[LISTENER: Hi. This is Beth from San Francisco. Leadership support for Radiolab's science programming is provided by the Gordon and Betty Moore Foundation, Science Sandbox, a Simons Foundation initiative and the John Templeton Foundation. Foundational support for Radiolab was provided by the Alfred P. Sloan Foundation.]

 

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