Dark matter and the end of answers

0:00This Monday.com ad was created by a team of people and AI agents. Reese, our content agent, wrote the copy based on our best practices, like mentioning Monday.com three times. That was the second. Johnny, our coordination agent, built the timeline and kept everyone aligned. Olivia, our human creative director, stayed in the loop because agents are great, but they don't always know when a joke lands. She had one note, tell listeners it only takes minutes to build an agent. So, minutes. Create your own AI agent today on Monday.com. Support for the show comes from Google Gemini. You know that moment when curiosity strikes?

0:36You're exploring a new city with a family and a sculpture catches your daughter's eye. What is that? Who made it? With Gemini, you can snap a picture and get a fully interactive breakdown of its history, architecture, and even hidden secrets. Gemini is built for moments like that. Whether you're learning something new, solving a problem, or looking for your next favorite thing. Google Gemini is here to help. Download Gemini, Google's AI app, or visit gemini.google.com to learn more.

1:10Take a look around you, wherever you are, the table, the TV, your own body. At a basic level, it's the same stuff as everything else. And everything you see if you look out the window, or even further out. The ocean, the rest of the planet, the sun, the stars. It's all matter. We can see it. We can feel it. But all of that stuff is just 15 % of all the matter in the universe. The other 85%, 85 % is something called dark matter. This kind of invisible, untouchable matter. But we don't know what it's actually made of. Scientists have been trying all kinds of things for decades to try and figure out what it is.

1:59But so far, they've got nothing. So what does it mean for science if we can't find it? If we can't answer arguably the biggest mystery in the universe? Today on Unexplainable, I'm going to talk to a physicist who spent years looking for this stuff and then realized he couldn't do it anymore. So he quit. because he started asking questions that went way beyond what he initially thought science was for. And stick around to the end of the episode for an update on some dark matter news.

2:50Joseph Howlett, thanks for coming on the show. Thanks for having me. So you are a science writer now. You used to be a physicist. What made you want to be a physicist? What got you so excited about it in the first place? Yeah, I mean, I always like these kind of big questions, like the questions humans have always asked, like, how did we get here? What is stuff made of? I had that instinct always to go deeper, right? Like, if you're in chemistry class, you hear that everything's made of atoms. And then you hear that atoms are made of electrons swirling around a nucleus. Then you hear that the nucleus is made of protons and neutrons.

3:26And then you ask, well, what are those made of? They say you have to take physics. Right. So if you do this enough times, you end up with a PhD in physics. And then you very quickly learn that there's a lot of things that we don't know. And you run up against that. Exactly. The unexplainable. And when you actually become a working scientist, that's the stuff you work on, right? So the decision I had to make is which of those questions to work on. And for me, it was obvious that it was going to be dark matter. At least like when I heard that everything I had been learning about is only one sixth of everything.

3:56at least for the picture I had of what science is supposed to do. That came as a real shock. So it's been a while since we've talked about it on the show. We had our first episode of the show on Dark Matter. But what is Dark Matter? And why did you get so excited about it? Yeah, so Dark Matter is a thing that we know is there, but we don't know what it's made of. Really, it's thanks to Vera Rubin. In the 70s and 80s, she cataloged how fast stars are moving around their galaxies. So she looked at all the stars. They're orbiting the center the same way we're orbiting our sun, right? But the problem with every galaxy is that all the stars are moving way too fast, especially the stars on the outside.

4:39Compare it to like a race car on a racetrack, right? If a car is going around the track and it speeds up and speeds up and speeds up, eventually the tires won't be able to hold it on anymore and it'll fly off the track. And when Vera Rubin looked at all the stars in all the galaxies, she was like, they're all going way too fast. They should all fly off into space. Everything, including our sun, should be flying off into space because there's not enough stuff inside to be holding it at the speed that it's going at, right? So either we don't understand gravity and all the laws of how much stuff it takes to hold a thing in going that fast, we're wrong about.

5:16or there's stuff we're not seeing that's gravitating, that's extra glue, like, holding that thing in. So if you imagine a race car, it can go way faster if you, like, stick a stake in the middle of the track and tie a rope to it, right? And it's like there's some additional thing we're not seeing that's holding everything in, that's holding all this stuff in. And that's dark matter. That's what we call dark matter just because we can't see it and we have no idea what it is. It's just a blanket term for this missing stuff. So it's matter that interacts with stuff via gravity, right? It can pull in these fast-moving stars at the edges of galaxies via gravity, but we can't see it.

5:57Why can't we see it? We don't know that. I mean, we just know that whatever this stuff is, it doesn't interact with light. It's somehow invisible. And when astronomers, physicists do calculations, the only way to have enough of this stuff to make sense of the way galaxies move, that's how they get to 85 % of all matter is dark matter or five-sixths of all the matter is dark matter. Yeah, that's where this number comes from, this why I say five-sixths of the universe is missing. It's because that's how much stuff you would need to add, how big that cloud would have to be to explain how fast the stars are moving.

6:31and since Vera Rubin, we've established it in all kinds of other ways. Like, you can make maps of the mass distribution of faraway things by looking at how they bend light around them. Our earliest picture of the universe, which is called the cosmic microwave background, it's like the light that was released very shortly after the Big Bang when the universe began to cool. That light tells us what matter there was then and it's very clear that there was five times more of some stuff we don't understand. Right, okay. Like, there's all of this additional evidence and all of it aligns with this five, six number.

7:02So why is it still such a mystery to us? Yeah, it's because we don't know what it is. I mean, like, it's a big thing not to know. Especially if you're like me, right? If you're asking these questions like, okay, what's in that? What's in that? What's in that? If you keep doing that, like, you want to know what stuff is at a fundamental level. Dark matter, if you picture some galaxy, it's like this shadow realm that's on top of the galaxy. You can't see it. And it's only, like, interacting with it through the way it tugs on things, right? All together. Through gravity. But what is that a cloud of, right?

7:34Right. I'm not satisfied that we know what dark matter is if we don't know what that cloud is. But scientists are trying to figure out what it is, right? They've been researching this for decades. Yeah. So one thing to say is that, like, shortly after Vera Rubin, there were these two explanations. There's either we're wrong about gravity or there's this missing stuff. Over the decades, that first hypothesis has kind of fallen apart. It's very hard to adjust gravity in a way that makes everything make sense. All of this evidence we have. We're pretty sure we understand gravity pretty well. It's a good theory.

8:07Yeah. So there's this missing stuff. And there was this kind of arms race. There was people trying to build detectors on Earth to detect this stuff that we know is going through us all the time, but we don't know what it is, right? So the next question is like, okay, let's figure out what it's made of by trapping it in a lab, right? That's how science works, right? Like there's this missing part of the universe, so you develop a theory that can explain it, and that gives you a testable hypothesis that you go build in a lab. And what's great for us is that theoretical physicists in the 80s already had an idea for a type of particle that might exist in the universe that exactly explained all the dark matter.

8:46Yeah, they were trying to map all potential particles, right? This is the standard model of physics? Yeah, the standard model of physics is the 17 building blocks, the Lego pieces, that everything we know about is made of, right? So it's the quarks that make up protons and neutrons. Electrons are one of these particles. And together, these 17 particles build everything that we can see, right? But it only explains one-sixth of everything, right? Like, we know that it doesn't account for this extra stuff, so we know that it's incomplete. And we had some kind of predictions, like there may be empty spots on the standard model.

9:20And what you're saying is that one of those empty spots would be the dark matter particle. Yeah, it was really convenient. And physicists like convenience, right? It's Occam's razor, like the simplest explanation is the one you go for first, right? And this is what's great about this theory they had in their desk drawer, is that it interacts gravitationally. It goes through us like a ghost, right? Like we knew about dark matter. But very, very rarely, on rare occasion, the ghost becomes corporeal for just a second and smashes into one of our atoms. Wait, that's the theory? That's the theory. Okay, okay.

9:55This particle that they had in their desk drawer, it explains all the dark matter, but in addition to its gravitational pull, there's a very, very, very weak coupling to the normal stuff in the universe. So dark matter is going through us all the time. Very, very rarely, imperceptibly rarely, one of those particles smashes into one of our atoms. We don't feel it. Got it. But that means that you can build a detector of regular matter to detect that. And that was key, right? Because that meant that, okay, we can, on Earth, look for this particle. And this is where your research enters into the picture, right?

10:27This is when you became a physicist. What kind of experiments were you working on? What kind of experiments are out there to find the dark matter particle? I mean, the way things went down is Vera Rubin and others convinced us that there's this missing stuff. And then theoretical physicists said, oh, we have an idea for what this missing stuff might be made of. And you can build a big detector. A detector is just a tank of atoms that they light, the tank lights up when one of the atoms gets hit, right? I said - Gets hit by a dark matter particle. By anything. Oh, by anything, okay. So when we get hit by a dark matter particle, you don't notice.

11:02You have a tank of liquid xenon, for instance, which is a cryogenic liquid. It's kind of like liquid nitrogen that you play with in a lab. Okay. When a xenon atom gets hit by a particle, it lights up. So that's all a detector is. So they said, okay, if I put a detector on this table, it would see stuff all the time because there's particles coming from space. Got it. So you would never see the dark matter particle that interacts once in a year or something. So it wouldn't work here, but it would work underground. So I was working to build this big dark matter detector underneath a mountain, one of Italy's biggest mountains.

11:35Okay. Yeah. So dark matter would go through the surface. It would go all the way into this underground lab or wherever. And the idea would be that maybe there we could see dark matter hitting some other atom. It would go through this whole mountain in Italy. It would go deep into the center of the mountain. It would go into the lab. It would go into the detector. And 99.99 % of the time, it would go through the detector without doing anything. But the idea is, once in a blue moon, if you wait long enough, you make the detector quiet enough, one of those dark matter particles will become corporeal just at the right moment, smash into a xenon atom, light the detector up, and then we say, okay, we found dark matter.

12:15We know it's made of these particles. And then the problem's solved, right? Yeah, tell me about the mountain, the lab. Like, what does this look like in Italy? It's an interesting commute. Like you pile into like a little Fiat and you drive down these mountain roads, you go on the highway and the highway has a tunnel that goes through this mountain. But we don't go all the way through the tunnel. We go halfway through the tunnel and then there's this turnout for the scientists. It's like a little secret. There's a little secret entrance with these Italian guards who mispronounce your name and Olet, they called me.

12:47Okay. Amazing. And, you know, you show them your badge, you go through and then you're in this cavern. It's like a big underground cavern. It's kind of chilly. It's expansive. Is the ceiling like cave? It's cave. Oh, my God. Yeah, yeah, yeah. Yeah, it's cave. I mean, it's finished in different places, but you know that you're underground. It's a little claustrophobic if you're someone like me, but we'd never see the sun, basically, because you'd stay there most of the day when you're really working at it, yeah. Wow. I think I have a photo of you. Is this you in Italy? Yeah, this was, I think, 2019, something like that.

13:23Underneath the mountain, closing the giant detector. So you can see it's kind of a size of a very small sedan. This is the actual, so like this is full of xenon? It will be full of xenon. So where I'm standing will be water, basically. And this thing will be contained in vacuum because it has to be very cold, right? But first you have to build it and close it up. And that's what we're doing in this picture. What do you think 2019 Joe is feeling at that point looking at that detector? I mean, it was really invigorating to be like building the thing. Our experiments were working really well. They were getting very sensitive.

14:00And we were about to make that jump to cover the region of predictions. That was exactly what the theorists predicted. It felt not probable. Like, I don't know that I would have put money on it. But there was optimism around. Yeah, definitely. Then tell me when you started to feel differently. Yeah, so we ran this big detector, and I was working on the analysis. So you have all this data, you have, like, whatever, many months of this thing sitting quietly and looking for the light. And there was this one big Zoom call with my entire collaboration, people all over the world, hundreds of people on one video screen in all their different universities.

14:45And it was this moment where we were going to find out if the experiment worked or not. It had already run for a long time. We had already built out this big method for analyzing whether or not the data contained dark matter. And all at once, we were going to push a button, and the experiment was going to tell us whether, yes, you discovered dark matter, or no, you didn't. And I remember that moment when we pushed the button, we watched it churn through all this data and say, no, you didn't find it. And I remember watching what seemed like despair wash over everybody's face. I watched like the stages of grief in fast motion.

15:22What did you see on people's faces? At first, like a kind of denial. Like I think everybody was like, it's okay, it's okay. Like instantly they went from, I think, a sincere belief that we had a good chance of seeing it to like, okay, well, it's not the end. We can build more. like dark matter could just be a little more ghostly than we thought before, build a bigger detector. And we immediately started doing that. That was most of my PhD was building bigger and bigger detectors and waiting longer and longer. The bigger you, the detector you build, the longer you wait, the more sensitive you become to this rare dark matter interaction.

15:56But that day had an impact, like especially when I talked to young people who I was working with. So, you know, I was in Italy, I was going underground and you would have these conversations over lunch, over dinner, and you would get the sense that like nobody actually thought the thing was going to work anymore. Like the disillusionment, at least among young people was pretty universal. The professors who had spent their whole career working on dark matter, they showed more optimism. They showed more like, okay, well maybe the next one, but especially all those young people who had seen that first failure, I think they were shaken.

16:29Their faith was shaken. Do you remember any of those conversations? Yeah, I mean, I started taking like an informal poll, right? I would ask people, so like, what do you think are the chances that this detector we're building, the next one, the bigger one, will find dark matter? And they would say zero. They would say, no, it's not going to happen. So what does it mean for science if we never crack what might be the biggest mystery out there? We'll get into all that after a quick break.

17:07Support for the show comes from Square, the business platform that aims to help sellers become neighborhood favorites. These days, buying stuff is pretty easy with tap-to-pay. Maybe it's a breakfast sandwich at the corner cafe, a lunch break haircut, or some wall art that you picked up spontaneously on your way home. Square says every day we interact with businesses that rely on Square to make those transactions so fast and so simple. Square brings payments, point of sales, inventory, staffing, and online sales together in one easy-to-use system. Their hardware is sleek, simple, it comes with software that's intuitive to use in your day-to-day operations, and it also has AI-powered tools that help automate routine tasks, giving you more time back as a seller.

17:55Whether you are just starting out or growing from one location to many, Square can help you out. You can sell online, in-store, or both, and customize your setup as your business evolves. Right now, listeners can get up to$200 off Square hardware when you sign up at square.com slash go slash unexplainable. That is square, S-Q-U-A-R-E dot com slash go slash unexplainable. Get started with Square and build a setup that works the way you do.

18:30Picture it. Summer, you and your girls at your favorite patio bar, the sun's out, the breeze is perfect, and you're looking stunning in that new sundress. And what are we drinking? A Campari Spritz. It's just Campari, Prosecco, and soda water. Bold, iconic, and perfectly bitter, just like you. Check out official cocktail recipes at Campari.com. Campari Spritz. Stay bitter. Campari liqueur, 24 % alcohol by volume 48 proof. 2026 Campari America, New York, New York. Please enjoy responsibly.

19:07This is advertiser content from IBM. Cold take. My laptop works fine at room temperature, and most things on Earth do. If quantum computers can only function and behave quantumly at insanely cold temperatures, how will they ever become useful to most people? My name is Olivia Lanes. I am the global lead for content and education at IBM Quantum. I want to emphasize that actually cooling down a quantum computer is not really as hard as I think people think it is. It really is just the push of a button that can take your entire infrastructure down to 10 millicalvin. That is not the challenge, scientifically speaking.

19:49I also want to emphasize that in the future, we don't envision everyone having their own quantum laptop. Quantum computers are going to live in a data center. Data centers already have their own cooling infrastructure. It's not going to be something that you have to learn how to install and work on a personal level. But that doesn't mean that the discoveries made with the technology won't affect every person. quantum computing has the potential to touch almost every industry that you can probably think of if you would like to learn more you can do so at ibm.com slash quantum

20:37so it seems like there's two possibilities here either we are failing as a scientific community or struggling, I don't want to say failing, to detect the particle. We're not building big enough or quiet enough detectors. Or there's something about the nature of dark matter that makes it impossible to detect. Yeah, I mean, it could be that it's just this shadow realm that only interacts with our world through its gravitational pull. If that's the case, we'll always be in this place where we know it's there and we don't know what it's made of. Yeah. I mean, you sent me a conversation you had with Siska DeBartemacher.

21:19She's a philosopher. And she said something that really stuck out to me. It is entirely possible that dark matter only interacts gravitationally. And that would be a worst case scenario for physics. But like nature doesn't have to play nice. What do you think about that line, nature doesn't have to play nice. Unfortunately, what Siska's saying is that nature doesn't have to have made a dark matter particle that you can never know what it's made of, right? Like, we can only know what something's made of if we can trap it in a detector on Earth. Right. That's how we answered all the questions I asked in high school and college, right?

21:54We can never answer those questions for dark matter if it only interacts gravitationally. Right. Because you can never trap it in a detector. Gravity is too weak of a force. It just seems like such a tantalizing situation that we can see it doing all of this stuff. We see it holding galaxies together and spinning them faster than they should be. And we can't capture it. We can't detect it. It's horrible. Billions of them are going through us all the time. But we'll never know what they are. That's what I'm saying. For me, that runs up against my entire picture of what science is supposed to do.

22:31Yeah, so you've talked to a bunch of scientists and philosophers of science. Did anyone disagree with your perspective that science can't tell us the secrets of the universe, that maybe it's unreasonable to expect science to reveal itself in the ways we want it to reveal it? You know, when you put it that way, when you ask a scientist, does the universe owe us explicability, comprehensibility? They'll say, of course not. but if you ask them in any one situation what do you think is going to happen with dark matter including my former peers the people who said 0 % that our experiments would work, all of them 201 felt that at some point we'll figure it out I don't know what's going to happen but some genius will come along, some Einstein and change the paradigm and we'll learn that we were wrong about everything and everything will suddenly make sense all the physicists I talked to had this faith that I used to have and there's good reason for that.

23:27There's a reason for optimism. It has done a lot of things. We've overcome a lot of mysteries. But even if I'm wrong and I might eat my words tomorrow, I'd love us to find dark matter. There's a wall somewhere is what I've learned. Maybe this isn't it, but it could be this. You used the word faith. Sorry. No, it's fine. It makes sense to me. Is that what this feels like to you? Does it feel like some of the scientists you talk to have faith that you no longer have in what science is and how it's supposed to work? Yeah, I mean, I threw that word at some of them. My advisor, Eleanor Prelay, she threw it back at me.

24:12She said, how are you so certain, Joe, that we will never find this thing? And it's true. I think I've been so disillusioned that I've maybe lurched into pessimism. Another philosopher I talked to told me to lighten up. That was his professional advice. But I've become convinced that even if dark matter gets discovered tomorrow, which could happen, I could eat my words, right? I would love to. But even if dark matter gets discovered tomorrow, I now feel that there will be another wall down the road. If the wall we can't penetrate in our understanding isn't dark matter, It will be something else.

24:50We'll never understand everything. It's something that sounds obvious once you say it, but like the fact that there is means that I was asking the wrong thing of science. It means that I was wrong about what science is. And maybe that means that there's other people who are misunderstanding the purpose of science. Maybe science is the thing that tells us that we can't know everything. And like, maybe that's the point of science. Maybe we're verging a bit into religion here, but it kind of feels okay. You know, I think about Maimonides, the medieval Jewish philosopher. His conception of God is that God is unknowable.