The Decibel - The hunt for dark matter, two kilometres under Sudbury

Episode Date: December 27, 2023

For the holidays, The Decibel is sharing their favourite stories of the year, with the producers taking you behind-the-scenes on how the episodes were made, what inspired them and all the tidbits that never made it into the original airing.***No one really knows what dark matter is. We just think it exists. And we believe it makes up 85 per cent of all mass in the universe. So how do you solve the mystery of something that is currently unknowable?Enter SNOLAB. This underground, clean lab is located in Sudbury, Ontario, and researchers there are running experiments to try to solve this cosmic query. Decibel producer Madeleine White, along with Globe science reporter Ivan Semeniuk, go two kilometres underground to visit SNOLAB and bring you up to date on the lab’s quest to discover dark matter.This episode originally aired on August 10, 2023Questions? Comments? Ideas? Email us at [e-mail]

Okay, so this week we're going to go through some of our favorite episodes of the year as picked by our producers. So to start, I've got Madeline White in the studio with me. Hey, Maddie. Hey, Manika. So as one of our producers, you picked one of your favorite episodes of the year. So what is this episode and why did you pick it? So I picked our episode on Snow Lab, which is a physics laboratory buried deep underground in Sudbury, Ontario. I actually got the chance to go there this year, and I thought that this was a great episode to re-air

because how often do you get to go two kilometers underground? Exactly, yeah. I mean, I remember when we did this, it was a really exciting thing because you actually got to go out for a couple of days and do this in the field. Was there anything from that trip to Snow Lab that that didn't actually make it to air in the episode? The one thing that I didn't unfortunately get good audio of was when we were walking through the dark, dusty mine where Snow Lab is located. I talk about how there's this transition into a very clean, sterile lab. And I mentioned that I had to have a shower myself to get all the mining dust off me. But what I didn't capture audio of beyond the shower was my gear got its own little shower,

essentially. So some technicians took all of my equipment, including my recorder and my mic and my headphones and everything. And it went into a facility that was called the quote unquote car wash. And they actually like sterilized all my gear. And it took like half an hour. I was without a recorder, which I got to say, you know, as an audio journalist now, I felt kind of naked. Without my recorder. I know. Okay, so we're going to think about Snow Lab again. Are there any updates since then?

Yeah, so I recently caught up with Dr. Jodi Cooley, who's in charge at Snow Lab. And she told me that they've had some exciting news since I was there earlier this year. So a big part of the audio documentary is about one specific dark matter detector called the Super CDMS. And she said that they've made great progress on it. When we were there, it was kind of just a platform. Now four of its main components, which they call the towers, are all underground and installed. And one of them is actually already in the process of taking data. We are anticipating that perhaps we'll see some science results from that tower this coming summer. So for 2024, she's also thinking about how to make Snow Lab into more of an intellectual hub. So we want to make this a place where people

come to not just go underground and build their experiments, but they come to exchange ideas, talk about science. They spend time doing science here. And they're also going to be piloting a program for students to come to the facility and learn about particle physics there as well. I also asked her about what she hopes will happen in the next year in terms of all the various experiments that are underground? The experiments that we have that are under operations, I want them to continue to operate taking high quality science data and publishing results. So I want them to remain sort of world leading. And we're always looking for what is that next idea that we can bring into Snow Lab so that Snow Lab continues to support and produce great science. Fascinating. Well, let's head back to Snow Lab. Thanks so much, Maddie.

Okay, so I'm here with producer Madeline White. Maddie, great to have you here. Hey. And you brought a piece of tape with you. So let's just play it and listen to what you have here. So I'm in the washroom here at Snow Lab. and the reason why I'm taking a voice note in the washroom is because this is the furthest underground toilet in the world, and the noise it makes when you flush the toilet is quite something. Oh my god, that's like an airplane taking off. What's happening? Oh my god, I loved your reaction. You literally jumped in your chair. I was like, what is happening? What is that? Okay, so why were you at the toilet that is the furthest underground, Maddie?

How did you find yourself there? So earlier this year, I went to Snow Lab. This is the Sudbury Neutrino Observatory Laboratory in, you guessed it, Sudbury, Ontario. And this scientific station happens to be two kilometers below the surface in an old mine. Okay. And so why were you there in the first place? Yeah, there are definitely more convenient bathrooms. So I didn't need to just travel two kilometers underground to use Snow Lab's toilet. I was there because I was trying to see how scientists are trying to unravel one of the universe's greatest mysteries, dark matter.

Okay, dark matter is one of these things I feel like I hear about and I've tried to understand, but it's hard to understand. Like, what exactly is it? This is actually like the question. They are trying to understand what it is, because the reality is we don't really know. We don't really understand dark matter. The thing we know about dark matter is that we think it represents 85% of all the mass in the universe. Wow. Okay. So a huge portion of the universe. But I mean, this is kind of esoteric in a way too, right, Maddie? Like in terms of our day-to-day lives, there's a lot of other scientific problems that people are trying to solve. We just went through a pandemic, right?

There's a lot of other things going on in the world. Why is it important to study something like dark matter, which we don't even really know what it is? Yeah, and we don't know if knowing what it is will give us any specific benefit. For me, the pursuit of this kind of science is just about reminding us about how mysterious the universe really is and how we're just just this tiny, tiny part of it. Like we're we're 15 percent of all the mass. And maybe that if, you know, this tiny fraction of all of that mass is trying to understand the universe a little bit better for the time that we have here in this universe. Like maybe we will learn something about ourselves along the way. So today, Maddie, you're going to take us on a journey

to try to understand what dark matter is. Yeah, and we're going to have to go deep underground for this hunt. Sounds amazing. I'm Anika Ramon-Wilms. And I'm Madeline White. And this is The Decibel from The Globe and Mail. It's about 5.20 in the morning. I'm here in Sudbury, Ontario,

walking through a hallway of a Hilton hotel while I wait for my ride to take me to Snow Lab. I'm exhausted, but I'm really excited. And it's very quiet here in Sudbury right now. And cold and rainy, it's like 10 degrees out. Despite that, I'm dressed in spandex shorts and a t-shirt and a rain jacket because when you get two kilometers below the earth i'm told it gets very hot so yeah i'm just hanging out here waiting for my ride and here comes my ride i'm going on this journey with globe photographer and videographer Patrick Dell.

Hey, Patrick. I'm already recording. Excellent. Nothing like wearing shorts at 5.30 in the morning. I know. Also, it's so cold. And science reporter, Ivan Semenik. Hey, Ivan, can you tell me where we are? We are at the entrance to the Snow Lab physics laboratory at the Crichton Mine in Sudbury, Ontario. Snow Lab is located just outside of Sudbury proper.

If you haven't been to Sudbury, you might know it as the home of the Big Nickel, which is exactly what you think it is, literally a giant statue of a coin. Sudbury is a mining town. And Snow Lab is located inside one of the region's oldest mines. Snow Lab was originally built in the 1990s with the goal of detecting solar neutrinos and studying their behaviors. But since then, it's expanded to look for dark matter. There's a good reason why this scientific laboratory is so far underground. Here's how Dr. Jodi Cooley,

Snow Lab's executive director, explains it. The reason that we're underground, it's so critical to the success of this program. And the reason is that when you're on the surface of the Earth, you're constantly being bombarded by something called a cosmic ray. It is a proton or a neutron from outer space that essentially smashes into our atmosphere

and creates all sorts of other types of particles. We use the Earth as a filter to filter out those particles. And so those particles don't reach our detectors. If they did reach our detectors, they would be making noise all the time. Getting down to the lab is its own adventure. First, we change into miner's gear because we need to be highly visible and decked out in safety equipment. Yeah, I'm going to outfit you with a full set of mining gear. We're going to get our herd hats, our cap lamps. We'll get a set of tags. We'll get a high-vis one-piece suit, a miner's belt, and some boots and gloves.

Okay, I'm not going to lie. Like, I look a little ridiculous here. Picture a highlighter yellow jumpsuit lined with orange reflective safety tape. I look like I was going to an underground rave dressed as a rejected member of the village people. The last piece of equipment I'll need to get down into the mine shaft is a little unexpected. I'll let Snow Lab's senior communications officer Mike Whitehouse explain. So the air pressure changes a lot and the remedy is the same as an airplane. Come.

If you're interested. That's a great idea. We line up in this room where miners and scientists mingle. We're all waiting for our ride down. It's a double-decker elevator called The Cage. I kid you not, it is actually referred to as The Cage. If you refer to it as the elevator you will be last at, it's The Cage.

All right, we're going to head down. Everyone heads down? Yeah. Okay, so I'm just walking down this ramp, fairly wide ramp about the width of the vehicle, heading down towards the deck, and then I'm going to get into the cage to go below ground, 6,800 feet, into Snow lab. There is no door in this elevator slash cage, just a metal gate to keep our limbs safely inside. As we're descending, the rock face is flashing by us.

We're dropping at a speed of about 2,000 feet per minute. That's over 35 kilometers per hour. Oh, and this elevator has no lights. So in this cage, we are standing shoulder to shoulder. That's how full it is. And it's dark. The only light is the light from somebody's headlamp standing beside me. About five minutes later, we're out and in a dark mining tunnel.

The miners who get off with us, they get to do the rest of the journey in a tram that scoots off, leaving us literally in the dust. We, however, we get to walk. So we're about to head down the drift. That's Ivan again. We have more than a kilometer to walk. We're already about to head down the drift. That's Ivan again. We have more than a kilometer to walk. We're already about two kilometers down, so a bit of nomenclature here. If it's a vertical movement, you're going down or up a shaft.

We're moving horizontally now along the drift, so really only halfway through our trip. Good choice. We just passed a little room that the door was open to and spray painted on the wall in red spray paint were in giant letters, Please Keep Clean. There are other labs in the world that study dark matter and some of them are even underground like Snow Lab. But this lab here in Canada, under a whole bunch of Canadian shield rock,

gets to hold one very specific world title. It is the cleanest, deepest scientific lab in the world. Cleanliness is a big part of Snow Lab, to make sure that we don't bring any sort of particulate matter into the lab, which is very sterile. The cleanliness is not just scientists being neat freaks. It's a crucial condition for the hunt for dark matter. Because despite dark matter having a substantial effect on the universe through gravity, we think it might be incredibly tiny.

And to detect something so abstractly small, you need to have as little interference as possible. Even the smallest dust particle or speck of dirt could contaminate the experiments. And to keep this level of cleanliness, there are a number of steps that we have to complete before we can actually enter Snow Lab, as Mike Whitehouse explains. And so can you explain what's about to happen next here? So we're going to wash our boots, get all the mine dust off our boots, because they are by far the most covered parts of our bodies. And then we are going to enter the car wash area. All of the equipment that you brought that was not double bagged is going to have to be left and washed.

So the microphone you're recording me with right now for example. And then we are going to strip off all of our mind gear and we're going to go through the shower procedure and get into the clean Tyvek suits so we can enter the lab. When we get into the lab though you'll find it's air-conditioned and it's very bright kind of like this but the walls are a lot cleaner and after a few minutes you'll find it hard to believe that you're two kilometers underground. Honestly, I'm sweaty enough I need the shower. I'm sad to tell you that they took away my mic for the showering, so no sounds from that.

But when I get out, I enter the lunchroom first. And honestly, mic is right. It doesn't feel like you're underground. It feels like you're in a generic, windowless lunch space. The walls are shiny and white. The ceilings are high. There's even coffee. And Wi-Fi.

But then you walk into where the experiments are taking place, and you're reminded, oh yeah, this is very cool. Welcome to Snow Lab. This is where the magic happens. We'll be right back. Okay, let me ask you a question. So how do you look for something you know nothing about?

Here's how Snow Lab's Dr. Jodi Cooley thinks about it. So how do you cope when you've lost your keys in your house, right? You're like, okay, let me try to think. So if I lost my keys in my house, I might try to think backwards and steps of where was I last? And I would start eliminating, well, my keys aren't in the living room. My keys aren't in the mudroom. My keys aren't in the car. They're not in the garage. They're not in my bedroom, right? You would slowly work through your house until you found your car keys. So I would say coping with looking for dark matter is something the same. Like we do have some idea of what dark matter might plausibly be. Like what is plausible mass for? What is a plausible

interaction strength? So we start looking for plausible dark matter candidates in plausible areas. And then as we rule it out, we exit out and we go to sort of the next space. So I would say looking for dark matter is kind of like looking for your lost keys in that way. There are 11 experiments that are either up and running or in the process of being built at Snow Lab. Some study fruit flies, some are looking for supernovas, but most are looking for dark matter. They have sci-fi sounding names like Sensai, Pico, and Deep 300. And one of the most sensitive dark matter experiments in the world is currently being built here.

It's called the Super CDMS, which stands for Super Cryogenic Dark Matter Search. Can we head to Super CDMS? Sure, yes, yes, let's do it. When we get to Super CDMS, it's still being assembled. Right now, it just looks like a very precisely measured round dance floor, built specifically to be in an active mine. So this platform was designed specifically to decouple the experiment from vibrations in the mine. So we call it the seismic platform.

That's Dr. Andy Kubik, one of the research scientists working on this experiment. If you look really close underneath, you can see that it's actually sitting on springs in the form of coiled wires, so those keep the detectors from vibrating if the ground does. One of the most striking things about SuperC CDMS is the sound in the room. The loopy nature of this mechanical sound almost makes it sound like we're in an underground rave. But really what we're listening to is the hard work of specialty fridges used to keep the experiment's sensors very, very cold. Here's Dr. Kubik.

That's like the way we would like to describe it as colder than space. Only the detectors have to be that cold, but a lot of the electronics have to be fairly cold as well, like liquid nitrogen temperature roughly. Those detectors Dr. Kubik mentioned, they need to be cooled to almost absolute zero. I asked Ivan just how cold that actually is. It's hard to think of absolute zero. I mean, on a temperature scale, it's minus 273.15 degrees Celsius, right? So it has a value.

It's a very low temperature. That idea of being just a few hundredths of a degree away from absolute zero is going to take you to a point where the inner noise and the movement inside the detector is dampened out and a passing particle like dark matter, if it interacts, would make itself visible. Super CDMS, it's got these wafers, these hockey puck size, a little bit larger than hockey pucks, disks of very pure metal, silicon and germanium. And you can almost imagine the atoms in these metal like a crystal lattice. So imagine this kind of lattice

almost like bed springs or something just sitting there. And the idea is if a dark matter particle passing through comes close enough to one of the nuclei of the atoms in these detectors, it'll jiggle that atom and the jiggle will kind of resonate through the whole crystal. But the trick with the detector is that etched onto the surface of these disks is this superconducting material that's just at the threshold where electricity can pass through without resistance. The idea is that one of these little jiggles would break that state. It's almost like, imagine a tiny little fly landing on a balance beam and suddenly shifting the balance. So then the trick is, well, how do you know if it was dark matter or something else?

And that's where you start to have to accumulate statistics. You have to run the experiment for a long time, account for all the possible sources of jiggling, and see if there's something left over. So if dark matter is somewhere in the mass range of a proton, or up to 10 times a proton, super CDMS would be perfect for finding it. But all of this equipment comes at a cost, $42 million specifically. Yes, that is a lot of money, but to put it in context, Elon Musk spent $44 billion on Twitter or X or whatever it's called now.

So anyways, this experiment is being funded by the U.S. Department of Energy, the National Science Foundation, and the Canada Foundation for Innovation. Yeah, this is a big bet, you know, due to the footprint, the cost, and the investment from Snow Lab. For me, this is like so personally exciting to see this. Like, this is like almost my whole career. Well, certainly my whole career since entering dark matter. There is no denying the excitement in the room, even though this experiment won't be fully operational until early 2025. But people here are really hopeful that this, this project might be the one that finds dark matter. I hope in my tenure as director here that we have another Nobel Prize for the lab.

And I think if we had a positive detection and we were first in Super CDMS, I think a Nobel Prize would be on its way. It wouldn't be the first one for SNOLAB. The facility's founder and principal researcher, Arthur MacDonald, won a Nobel Prize for his discoveries about how solar neutrinos behave. But even without the top prize in science, running these experiments gives Canada huge cachet, according to Dr. Cooley. This is great for Canada.

What we need to do now as scientists, as lab staff, as leaders in the field, is to continue to push the science forward so that Canada can remain number one in underground science. That's what we want. When people think about doing underground science, we want them to think of us first. But here's the thing. Even with equipment as sensitive and complex as super CDMS, there is no guarantee that the scientists at Snow Lab will succeed. I want to know, and this is not specific to Snow Lab, but as a scientist who's devoted their career to dark matter, what if dark matter is unknowable?

Well, that still tells us something. I think, you know, this almost goes back in my head to like, why do you do fundamental science at all, right? We're trying to increase the knowledge. But to me, it's like, not just the end of the journey, not just what is the answer at the end, but it's the entire journey and how you get there. So in getting to a point where we felt like, okay, dark matter, trying to know anything more than it works through gravity, okay, that would be extremely disappointing. But along the journey, I would think about all of the advances we had made. We have made huge advances in sensor technologies. We've made advances in computing, we've

made advances in learning about different algorithms and data training. And so I think, you know, trying to look at the endpoint, like it's always disappointing if you get there, but I think if you look at it as the whole journey and the whole collection of knowledge that you've gained along the way, the serendipity of things you might have discovered, those are the positive effects that you would have to take away from it. Even though we're talking about physics, this story feels unshakably metaphysical as well. And it reminds me of Carl Sagan,

the scientist who made the curiosities of the universe accessible to the general public. This is where we live, on a blue dot. That's where everyone you know and everyone you ever heard of and every human being who ever lived, lived out their lives. It's a very small stage in a great cosmic arena. In one of his books, he says science is like a candle in the dark. Observation by observation, science is illuminating the world around us.

Even when an experiment fails, the light from the candle gets a bit brighter. I often think scientists must be the most positive people that I know because the number of times that you fail at science before you succeed is remarkable. But these scientists, you know, like they don't just give up and throw their hands up in the air. They like pick themselves up and they say, all right, what's next? Every failure to observe dark matter is an opportunity to think about how can we do it better next time? That's it for today. I'm Mainika Raman-Wells.

Our summer producer is Nagin Nia. Our producers are Madeline White, Cheryl Sutherland, and Rachel Levy-McLaughlin. David Crosby edits the show. Adrian Chung is our senior producer, and Angela Pachenza is our executive editor. Thanks so much for listening and I'll talk to you tomorrow.