The quest for dark matter

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1:09Welcome to Inside Science from the BBC World Service. I'm Roland Pease, standing in for Tom Whipple, who's off recording a future episode at one of my favourite places, CERN, home of the Large Hadron Collider, where they discovered the Higgs boson and where they hope to uncover many more secrets of the stuff of the universe. Though we've got our own mysterious stuff to talk about, dark matter, which has frustrated physicists for decades. We've also got hope for corals, increasingly endangered in this warming planet,

1:42but hope in the form of probiotic therapy. Also, veteran environmental journalist Fred Pearce has reasons to be cheerful. When I was a young journalist, we were talking about acid rain. Nobody much talks about that now because we fixed it. Lead in petrol, we fixed that. So we have quite a good track record of being able to address problems. Well, you can find out more about that later in the programme. Also, I'm joined by Kit Diase, Professor of Maths at Bath University, ever watchful of what's going on in the world of science. Thanks for joining us, Kit.

2:13What have you got for us? Yeah, so I'm going to be telling you a little bit about a new method of dating artefacts and I'm going to be telling you about polygons on Saturn. Polygons, polygos, poly, here we are.

The quest for dark matter

2:25The quest for dark matter just got interesting. On Tuesday at three in the afternoon, researchers on an international project called LZ reported they'd seen a ping in their detector some years ago that, after a lot of scrutiny, looks different from all the other thousands of pings they'd recorded and might just be the signature of a piece of dark matter passing through an underground mine in South Dakota. The embarrassment for physicists is there's six times as much dark matter as there is the normal atomic stuff that we're made of

2:57and which is studied at places like CERN. Astronomers know about it, they can see its effect on the motions of galaxies. And yet here on Earth, despite decades of increasingly ambitious experiments, there's been no sign of what it might be. One of the early experiments hunting the stuff was a detector sitting in a mine at Bulby on the Yorkshire coast called Zeppelin, the Z in LZ, whose operators later teamed up with the LUX collaboration in South Dakota and have been waiting for something to happen since 2021.

3:30Rewarded now with a single, inexplicable ping from inside their seven-ton detector. Kimberly Palladino, Professor of Physics at Oxford and also a member of that LZ collaboration, explained to me that when you're looking for something as mysterious as dark matter, you have to start with some assumptions about what it might be. Dark matter could be a lot of things. And the type that I particularly look for is some sort of tiny thing that has mass, but no electric charge and no other known forces except gravity acting on it.

4:04But there could be novel forces and it could interact with things like the Higgs boson. So we know about it from gravity. But, you know, in our heads, it's this tiny, tiny billiard ball, usually, that bounces into things but doesn't interact with magnetism or light or charge for the most part. And it's the most passive sort of experiment then that you do with this, is you just fill a vat with atoms and hope that one day one of these billiard balls

4:36will ping off one of those atoms. Yes. And so we build a very special vat in that we don't want there to be other regular things bouncing around in it. So we make sure we make it with low radioactivity materials. We put it deep underground. We put vetoing detectors around it. And we use a target material that has very little residual radioactivity in it, liquid xenon. And then, indeed, we do just wait. But there's a lot of effort in that waiting. Yeah. I mean, I suppose a rare event, when it happens, you've got to try and make sure that you don't miss it

5:11and that you get some information. And that, when it happens, as I understand it in this case, was actually back in June 2023. Exactly. It was back in 2023. And we really started looking at this data set in 2024. And so we've been doing an analysis on it for quite a long time. What we see are flashes of light in our detector. And some of this light comes from xenon giving off scintillation light. So immediately when xenon gets hit, we see a flash of light. And then in our detector, we put a big electric field and we extract electrons from the detector out into some gas where it makes more light.

5:47This is kind of exactly how neon lights work. And we have detectors that sense that light. So we get two flashes of light that we interpret it back to being one atom of xenon that got hit. I mean, looking at the paper, in the time period, you got 1,700 other flashes of light and so on. What was it about this one that you said, yeah, this is, you know, this is intriguing? Well, that 1,700, we see even more than that. That's even after some cuts against kind of really boring things.

6:18In our detector, we can tell if we initially hit the nucleus of the xenon atom or the electrons around it. And luckily, most of the types of things that are natural backgrounds for us, being electrons and high energy photons called gamma rays, they're always going to interact with the electrons first. And so those 1,700 events were that type. This one looks really special because it looks like we hit a nucleus. And only did we hit a nucleus, but we hit it with a lot more energy. Right, so it's a kind of head-on smack of some sort, you think?

6:49A bash, yeah. So it looks like the equivalent of 250 keV of energy in nuclear recoils. And this is a number that doesn't make much sense. But for our types of low energy searches, this is a lot of energy. It's very little for the big high-energy particle physics colliders. But for the types of searches we do, our previous on dark matter searches really went up to about 50 keV in nuclear recoil energy. This is five times more than where we even planned our searches under the most boring types of dark matter that we were going to be looking for.

7:23So, well, this goes to something. I mean, this experiment has been running since, I don't know, this has been running for a few years, I guess. It's been running since 2021. And there have been experiments, smaller experiments like this, going back decades? Yes, multiple decades. I mean, my point is, it feels like we've been waiting an awful long time for anything to happen. We have. And that maybe lends itself to thinking that this is a signal that it is a more rare, more unexpected one. We have no idea.

7:53It's in my head I have that old pop song, one is the loneliest number. We just can't tell with one event. And it's the strangeness of statistics. At the moment, can you tell anything about what this dark matter particle might be, if that is what you've recorded? Is it something that's light, like an electron, or something that's sort of about the same mass, let's say, as a proton? This is going to be much heavier. So at least kind of over kind of 200 times the mass of a proton might be even more like a thousand times the mass of a proton.

8:30So it's a much heavier type of dark matter. And I think this is also why the particle physics community is really excited for this, because it links a lot more with the types of dark matter models that the collider experiments at CERN could look for. And indeed, I've seen already theorists coming out with great descriptions that this might be something like a Higgsino. Look it up on Wikipedia if you want to find out more. That was Kimberley Palladino of Oxford University and also of the LZ collaboration and of a proposed successor project called XLZD, which might take up residence at Bowlby Mine in Yorkshire.

9:06Anyway, it's an excellent week for us to have on hand a mathematician, Kit Yates, from Bath University, to talk about the statistics of these experiments. Because, Kit, you know, a single ping is, for me, more like an anecdote than data. But Kimberley seems to think you can make out more from it than just that. Yeah, and the scientists who are doing these experiments suggest that they might see an event like this just purely due to known background processes, so non-dark matter processes.

9:37On average, once every 200 times, they run this experiment. So a 0.5% chance of this result happening, even if no dark matter were detected. So, you know, to put that into context, it's like tossing a coin eight times in a row and you get eight heads. That's the sort of unlikeliness that we're talking about if the coin is genuinely fair. It's unlikely, but it's not impossible. And like you say, one event just isn't really quite enough. So the way that dark matter is likely to be confirmed is if they see similar results in the same facility or even better at other facilities around the world,

10:09which will give them more confidence that this wasn't just a fluke. Well, I could tell that Kimberley is certainly pretty excited by the fact they had detected anything. So, well, fingers crossed for them.

Polygonal waves on Saturn

10:18While we're thinking of such cosmic things, Kit, one of the stories you've brought along involves mathematical figures in space. Yeah, exactly. So for a long time, decades, in fact, scientists have known about a seemingly mysterious hexagon that encircles the North Pole of Saturn. It's this remarkably stable six-sided phenomenon, should we say, which has persisted since at least when it was first spotted by the Voyager mission in 1981. So over 40 years now. And there are lots of competing hypotheses about how the hexagon on the North Pole developed.

10:48But interestingly, if you read the Wikipedia page for the Saturn hexagon, it has its own Wikipedia page. If you read it a couple of days ago, you would have read that there is no corresponding hexagon on Saturn's South Pole. But a paper just came out this week in the journal Science Advances, which reports the discovery of a ten-sided or decagonal atmospheric wave encircling Saturn's South Polar region. So the authors first spotted this in 2023 using the Hubble Space Telescope. And by 2025, it was well enough established to be visible from ground-based observatories.

11:20As a mathematician, you must be absolutely fascinated by the sort of regular shapes. I could imagine some kind of circular wind or cloud pattern doing that. But having corners in it seems bizarre. Yeah, that's exactly the question that fascinated me. Why does Saturn have these polygonal waves? And the answer is because the planet is rotating and it causes a jet stream to form, very much like the familiar jet streams that we have on Earth. You know, we have one which encircles the North Pole and another half the world away encircling the South Pole. And people probably know the jet stream isn't just one continuous jet of wind that blows from east to west.

11:53The wind path actually meanders in sort of large north-south oscillations called Rossby waves. This is what gives us our sort of variable weather patterns in the UK and much of the rest of the northern hemisphere. And actually, the same thing is happening on Saturn. Only on Saturn, the jet stream is really narrow and strong because Saturn rotates very quickly. So instead of looking like a looping wave, the peaks and troughs get flattened out and they look like a polygon when they're viewed from above. And those corners aren't actually sharp corners. They're just the peaks of the wave. And they're actually in reality quite smooth.

12:23But they just look sharp because of the huge scale of the wave. You're listening to Inside Science from the BBC World Service. Tell us what science you think we should be investigating. Our email address is insidescience at bbc.co.uk. Healthcare can feel complicated. That's why Optum uses technology to connect the people and processes that make healthcare easier, more affordable, and more effective. We're making it clearer for you to know exactly what your benefits cover.

12:55And to help you better manage your health, we're coordinating care between your doctors and your technology. We believe better, simpler healthcare is always possible. That's healthy optimism. That's Optum. Visit Optum.com to learn more. Quick one before you jump back in. You're listening for ways to help teams move faster, make sharper decisions, and turn scattered context into work they can use. ChatGPT for Business can help. ChatGPT for Business gives teams a shared workspace with admin controls, permissions, and access to work and codecs in ChatGPT.

13:29This means your business can move from question to answer and code to rollout quicker. Join over 10 million business and enterprise users worldwide already using ChatGPT for work. Download the ChatGPT desktop app or contact sales to learn more.

Probiotic therapy for corals

13:48Now, probiotics are all the rage in help yourself health. Bacteria in yogurts typically that boosts the vitality of the microbiome in your gut that sits there doing good things for us. The surprising news this week is that probiotics may also be good for corals, which are increasingly being denuded and threatened with extinction by bleaching events triggered by recurrent marine heat waves. When I called microbiologist-turned-ecologist Erica Santoro, who's been testing the probiotic treatment on reefs in the Red Sea,

14:20I had to confess I'd never even thought about the possibility of a coral microbiome. Every single organism on planet hosts bacteria and other microorganisms, and this is not different in the ocean as well. So the corals also host a big amount of bacteria and microalgae, so it is a big mix and soup of other microorganisms that live together with these coral hosts. So we call these a holobionte because they actually work together and evolve together as well.

14:51You mentioned there the microalgae, and these actually live inside the coral animals and give them the colour, but also help power them through photosynthesis. But when there's a heat wave, they get lost, don't they, from the corals, and that's a trouble. The coral itself, they are translucent. So the tissue are not the colour that we see, but that is given by this microalgae that lives inside the coral tissue. So they host a microalgae inside, and the microalgae produce a lot of compounds that are going to be used by the corals as nutrients and exchange the corals protecting this microalgae.

15:28The thing that happens when there is any stress, like the temperatures are raising in the ocean, there is a trigger which, like, causes a lot of stress in the microalgae. They produce a lot of compounds that are stressful for everybody, including the coral hosts. And a couple of processes can happen there that these algae can be expelled by the host, that they can escape, the cell can just, like, break apart, and, like, this mutualistic relationship, they just break up.

16:01But somewhere along the way, you thought that there was some way that using probiotics, in other words, adding extra bacteria to unhealthy coral would help them. Yes, so the idea here is we look at the coral and try to understand the beneficial relationships that exist between the coral and the microorganisms, and we isolate and manipulate those beneficial ones. Not giving anything that is extra or different to the coral, but something that's already native to them.

16:34I'm wondering how you do this, because it's a bit different from taking a teaspoon of yogurt. So what's the process? Currently, we are doing this in the ocean, so we are upscaling from the lab setups and bringing to the field. We culture those beneficial cells, we increase them in number, and put them in some syringes and apply on top of the coral. So this is going to create a kind of cloud of beneficial bacteria on top of those colonies, and we apply these often.

17:07So we guarantee that those corals are going to actually uptake those bacteria that we are offering to them. What difference did you see between the treated and the not treated coral? So we observed, first of all, some proxies that are related to coral health. One of them is observing how good they are doing this photosynthesis, and these were decreasing along the time when we don't treat them. But when we applied the probiotics with time, they were actually recovering. They were actually having a better photosynthesis in those colonies that were treated with probiotics.

17:41So we saw a good result. I mean, if you are seeing these corals being more resilient, so presumably somehow these bacteria are being taken up by the corals, but do you actually have any idea of what they're doing that makes the symbiosis with the microalgae and so on? How does it all work? Yeah, that's also like one of our questions. But what we know so far, they are probably working on kind of distressing a little bit the coral. So when there is like this bleaching or some thermal stress, there's a lot of reactive oxygen species that are produced by this microalgae

18:16that makes this relationship and the whole of the biome to like very stressed. They don't have time to recover and to kind of buffer those reactive oxygen species. And those bacteria can actually buffer that. They produce some enzymes and some products that can actually buffer this. So this is one mechanism. Another mechanism is those strains that we select. They really can fight against some pathogens. So when we have like some stress moments, like the microbiome of those corals, they can change and get unbalanced.

18:49That means that some opportunistic bacteria that live necessarily in the microbiome can increase in numbers. But those probiotic strains can fight against those pathogenic and opportunistic ones and can kind of reduce them in numbers. Corals in the world cover a greater area than just the United Kingdom. This would be, if it became practical, a huge effort. What are the steps before you even get that far? We have been observing like this positive effect and beneficial effect in different coral species

19:23for different reasons to protect against bleaching, mortality, even like against diseases. So we are really getting excited about like the results and we see that it really works. Now, I think our question is not if it has an effect or not, but how to apply this in a big scale. Erica Santoro is based at King Abdullah University of Science and Technology and the results of her experiments were just shared in the journal Cell Reports.

Environmental optimism with Fred Pearce

19:52And we're continuing with a tone of optimism here on Inside Science with the book Despite It All, a handbook for climate hopefuls. With the UN Environment Programme declaring that the idea of limiting global warming to 1.5 degrees is now a busted flush and CO2 being pumped into the atmosphere as fast as ever, maybe we need to think about what progress the human race has made in protecting the planet. And that's what veteran environmental journalist Fred Pearce has attempted in this short tome,

20:22one of six works on the shortlist for the Royal Society's coveted Trivedi Science Book Prize. Challenge one for Fred was to sum up his book in just half a minute. I spent 40 years reporting on the bad news of the environment and there's a lot of very bad news, but these things are still on our own hands and we sometimes forget that. I think many environmentalists become overtaken by the scale of the problems and they give up, really. Either that or other people just think there's no problem. But actually, there's all to play for.

20:52There are many doors that we can push that will open, whether they're technical fixes or simply the ability of nature to come back. It's one of the things that I find myself reporting more and more. Given half a chance, given a bit of spare ground, it will come back. It will restore itself. And there's something joyous about that. I have to say, Fred, you know, having read your reporting over the years, as you say, in the past, it used to be this river is running dry, this forest is dying, this species is no longer... Are you actually the same Fred Pearce?

21:23Or have you been taken over? Is this the wisdom of age? Well, maybe it is the wisdom of age, but it's the wisdom perhaps of thinking, well, we have no alternative but to fix these things and we have to look for the things that will work. Now, none of this says that the problems that we face aren't really serious, whether it's climate change or biodiversity loss or the many other things that we talk about so much. But we have to look for solutions. We don't really have any other option. I mean, one of the chapters tackles the population time bomb and the idea that there were going to be too many people.

21:55And that was a massive issue back in the 80s and 90s of the last century. And in a sense, your message seems to be that actually birth rates are coming down without all the aggressive interventions that were being discussed back then. Yes. I mean, I remember going to conferences in the 1980s where environmentalists were saying, we have to force people not to have babies, you know, have to be a draconian population policies. But what we've subsequently learned is that people have voluntarily, without any of those horrible population policing activities,

22:27have brought down their own birth rates, their own fertility rates. Really, because most people have discovered that in the old days, you had to have four or five children to be sure that two would get to grow up and produce the next generation. Now, with much better health services all over the world and much better hygiene, most people only need to. So there's a positive story here. Without being Panglossian about this, we can make things better. The other side of this equation is the ecosystems.

22:58Again, in your book, you often talk about the resilience of ecosystems if they are left alone to do their own thing rather than intervening. Yeah, I've looked quite a lot at the people talk about reforesting the world. Clearly, we've lost a lot of forests. Clearly, that's done a huge amount of damage to the climate and to biodiversity and many other things. It's a major issue. But we can have more trees. We are having more trees. And very often, I think that's going to happen not by having a mass spree of planting, but simply giving nature room to regrow.

23:31I've seen it in North America. The Appalachians, in fact, are a great example, because that was more or less deforested to destruction 100 years ago. And now there's a huge regrowth that's been going on. And the great majority of that has been natural regrowth. But we begin to see that in parts of the tropics as well. Even in the Amazon, you'll see the trees come back, given half a chance. There are technical fixed stories as well. I mean, there's a big chapter in the book about how... Well, again, when I was a young journalist, we weren't just talking about the population bomb. We were talking about acid rain.

24:02Nobody much talks about that now because we fixed it. Lead in petrol, we fixed that. The ozone hole, we haven't fixed that, but we're on the way to fixing that. So we have quite a good track record of being able to address problems when we deal with it. And maybe we're on the way to doing the same thing with climate change. Along with all your travels, a huge number of anecdotes in the book. Is there one that sort of, at the time, you thought was hopeless beyond repair? And actually, you've seen that it sort of encapsulates your optimism.

24:34I encapsulate my optimism. Actually, I think in the climate change story, because it is the biggest story. It's the one that involves everybody and everywhere. And I remember going to the Earth Summit in 1992, where all the world's leaders were there and they passed the Climate Change Convention, which said we were going to prevent dangerous climate change. Well, we haven't done that. But right then, they didn't know how they were going to do it. Wind turbines were just a few kind of windmills on a hill in California. Solar power was something for powering satellites, where you had no other option.

25:06And nobody talked about electric vehicles at all. And now all those are mainstream and cheap and becoming the dominant technologies. If you'd asked me in 1992 whether in three decades or so we would have got as far as we have, I'm not sure that I would have thought we would. We're not there, but it is a surprise to me how far we've got. And Fred Pearce on his hopeful Despite It All, which is published by Granter. Kit, despite my inner ear, I really couldn't help being swept up by Fred's optimism.

25:40There is a place, I guess, for accentuating the positive as opposed to dwelling on despair. Yeah, I think we all need a little bit of that. What I thought was really interesting was the idea that we need these optimists as well as the pessimists. You know, we need the pessimists to highlight the problem and the optimists to provide the hope. Because I think if you go too far down the doom spiral of pessimism, then you get to the point where you believe there's no hope, which causes inaction. It's a sort of positive feedback loop, like a vicious circle. But I think it's also important to note that optimism isn't the same as denial. So suggesting we don't need to do anything because everything's fine, because that also leads to inaction.

26:13So I think being optimistic about the potential to fix climate change isn't the same as denying its impact or its potential if left unchecked. Keep on trying. Yeah, absolutely.

Dating clay artefacts with magnetism

26:22Before we finish, Kit, you've got one more story for us. Yeah, this is about dating artefacts. So our listeners will probably be aware of a number of different ways of detecting art forgeries by determining the age of the artefact. Like radiocarbon dating, it works for things like canvases or frames on paintings which contain organic matter. But what if the artwork isn't a painting, but it's a sculpture? What if it's made of clay? Well, there's a technique published this week in the Proceedings to the National Academy of Sciences. It's based on a technique which uses the magnetism of the particles in the clay.

26:54So the idea is that the magnetic field of the large particles in a clay artefact, if it were fired today, they would point to where the Earth's magnetic north pole is today. But if something was fired, you know, 800,000 years ago, if we were doing things like that back then, then the Earth's magnetic field was reversed then and its magnetism would point towards the south pole where the magnetic north was then. But on its own, that isn't enough because if you change the orientation of the artefact, then that would change the direction of the magnetism. So you just have to turn it around and Bob's your uncle.

27:27Exactly, right. So that's not enough. But fortunately, the magnetism of the smaller particles of clay never actually really settles, but instead it accumulates, keeping a sort of record of the magnetic field they've experienced over time. But this accumulated magnetism can be erased by gently heating the object. But the key is that the longer it's been around, the higher the temperature you need to erase that accumulated magnetism. So by heating the object and determining whether this what's called viscous remnant magnetism has been erased or not, you can determine how old the object is.

28:00The higher the temperature required to erase it, the older the object. I mean, have they tried this on actual artefacts from the past? Yeah, they have. They've got a couple of nice pictures, actually, with the paper where they've tested older artefacts and more recent artefacts. And the researchers are hopeful that they can start using this method for museums to, you know, apply to articles which are of debated authenticity and even as evidence in trials about alleged forgery of these sorts of artefacts. Well, they probably won't find anything that old to date in my house.

28:32I'm sure it'll be very useful, though, in museums. Thank you very much, Kit, for joining us. Kit Yates is Professor of Mathematics at the University of Bath. And that's it for this programme. You've been listening to Inside Science on the BBC World Service with me, Roland Pease. Tom Whipple will be back, as usual, next week. Get more with BBC Podcasts, wherever you listen. Be the first to listen to your favourite shows, like Evil Genius, Good Bad Billionaire and You're Dead to Me, with a subscription to BBC Podcasts Premium on Apple Podcasts.

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