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  • NATURE PODCAST

Antimatter cooled with lasers for the first time

Listen to the latest science news, with Benjamin Thompson and Nick Petrić Howe.

In this episode:

00:44 Cooling antimatter with a laser focus

Antimatter is annihilated whenever it interacts with regular matter, which makes it tough for physicists to investigate. Now though, a team at CERN have developed a way to trap and cool antihydrogen atoms using lasers, allowing them to better study its properties.

Research Article: Baker et al.

News and Views: Antimatter cooled by laser light

09:27 Research Highlights

A dramatic increase in Arctic lightning strikes, and an acrobatic bunny helps researchers understand hopping.

Research Highlight: Rising temperatures spark boom in Arctic lightning

Research Highlight: Rabbits that do ‘handstands’ help to find a gene for hopping

11:53 Cost of invasion

Invasive alien species are organisms that end up in places where they don’t really belong, usually as a result of human activity. These species can cause loss of biodiversity and a host of damage to their new environments. This week, researchers estimate that the economic impact of invasive species to be over US $1 trillion.

Research Article: Diagne et al.

19:04 Briefing Chat

We discuss some highlights from the Nature Briefing. This time, the physics that might explain how a ship blocked the Suez Canal, and a new insight into octopuses’ sleep patterns.

The Financial Times: The bank effect and the big boat blocking the Suez

Science: Octopuses, like humans, sleep in two stages

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doi: https://doi.org/10.1038/d41586-021-00884-5

Transcript

Listen to the latest science news, with Benjamin Thompson and Nick Petrić Howe.

Host: Benjamin Thompson

Welcome back to the Nature Podcast. This week, antimatter gets cool…

Host: Nick Petrić Howe

And the global cost of biological invasions. I’m Nick Petrić Howe.

Host: Benjamin Thompson

And I’m Benjamin Thompson.

[Jingle]

Host: Benjamin Thompson

First up on the show, reporter Adam Levy is here to talk about an important matter.

Interviewer: Adam Levy

Our Universe is made up of matter, but matter is only half the story. You see, in physics, there’s also something called antimatter.

Interviewee: Jeffrey Hangst

For the lay person, we like to think of antimatter as kind of an evil twin of the matter that makes up everything that you and I know.

Interviewer: Adam Levy

This is physicist Jeffrey Hangst of Aarhus University in Denmark, and spokesperson of the ALPHA antimatter experiment at CERN in Switzerland.

Interviewee: Jeffrey Hangst

Now, we know in modern physics that for every particle that we’ve been able to observe, you can have an equal but opposite antiparticle. The interesting thing about these particles is they don’t exist normally because if they come into contact with normal matter they will annihilate and release a bunch of energy. So, they don’t exist. You have to make them in the laboratory.

Interviewer: Adam Levy

This annihilation is a serious problem. It means that any experiments with antimatter are incredibly tricky, as one wrong move and your antimatter bumps into some matter and is annihilated. So, given that these experiments are so challenging, why are Jeffrey and collaborators painstakingly studying antimatter?

Interviewee: Jeffrey Hangst

The answer is how could you not if you can? So, there’s some mysteries associated with these antimatter particles, and this dates back to the beginning of the Universe. If the Universe started as energy and it went on to evolve some mass, what happened to the anti-mass that should have been created at the same time? And the answer is we simply don’t know. Why did the Universe evolve to matter instead of antimatter?

Interviewer: Adam Levy

If physicists found some deviation in antimatter’s properties from the mirror image of matter that we’d expect, that could explain this fundamental question – why our Universe was created with a surplus of matter over antimatter. It’s certainly lucky for us that it did, since if there’d been equal amounts of both it all would have annihilated and there would be no stars, planets, humans or podcasts. In an experiment described in this week’s Nature, Jeffrey and the team were investigating how to slow down the movements of the simplest possible anti-atom – antihydrogen. Antihydrogen consists of just one antiproton and one antielectron. Slowing down antihydrogen could unlock experiments that will be able to compare anti-hydrogen and regular hydrogen with unprecedented precision. When I spoke to Jeffrey, I asked: Can you explain how the technique that you use, which is called laser cooling, works?

Interviewee: Jeffrey Hangst

Antihydrogen, like other atoms as far as we know, can absorb light, and atoms like to absorb particular colours of light. Now, light carries momentum, and when an atom absorbs one of its preferred photons, it gets a kick from the momentum of the photon, sort of like catching a heavy medicine ball if you’re standing on ice. Absorption of the light is dependent on how fast the atom is moving. So, the idea with laser cooling in this particular experiment is if I have atoms that are moving quickly towards my laser, they absorb photons and get slowed down, so I can slow down the fast ones and not mess with the ones that are already slow enough.

Interviewer: Adam Levy

Since laser cooling is such an established technique for investigating matter, why isn’t it straightforward then to just apply it straight out of the box and study antimatter with it?

Interviewee: Jeffrey Hangst

First, you have to have some antimatter. We could go on and on about what it takes to actually get to this stage of having the antimatter – that’s taken 30 years, to be conservative. You have to be at CERN, you have to produce the antiprotons, all this happening in an ultra-high vacuum so there’s no matter around. Once you’ve produced the antihydrogen, you have to hold on to it so that it doesn’t annihilate. Remember, matter and antimatter cannot coexist. Now, you have to shine a laser beam into that environment, overlap your trapped antihydrogen. This all takes a lot of very sophisticated gear to work at once. This is, I keep telling people, the most difficult thing we’ve ever done. For us, with antimatter, the lasers are a real technological challenge. You have to build it yourself. I should also mention that instead of milliseconds, it takes hours to laser cool anti-hydrogen. We’re really overjoyed that we’ve reached this level of sophistication now that we can first produce enough antihydrogen to laser cool and observe what happens.

Interviewer: Adam Levy

Well, what results do you actually get? How well are you able to cool down antihydrogen atoms?

Interviewee: Jeffrey Hangst

What we’re seeing is we’re slowing down fast antihydrogens by about a factor of 10. For us, that’s going from half a degree above absolute zero to maybe tens of millidegrees. We’ve already applied the laser cooling to the thing that we’re doing as our main motivation, which is to compare hydrogen and antihydrogen to see if they’re the same.

Interviewer: Adam Levy

What will this technique, this laser cooling, unlock in our study of antimatter?

Interviewee: Jeffrey Hangst

I would say that this is a complete game changer for what we’re trying to do. The first thing that we’ve set out to do is to measure the internal structure of antihydrogen and literally what we’re trying to measure is what colour of light does antihydrogen absorb? People have been studying exactly these kind of things in hydrogen for 200 years. So, there you get an immediate application of this. We’ll be able to improve our precision on this very fundamental test of whether matter and antimatter are the same. The second thing we’re setting out to do imminently is to study gravity. What happens if you have some antihydrogen and you drop it? So, laser cooling is a revolution for exactly that experiment. The colder they are, the more sensitive they’ll be to the force of gravity. So, these are two immediate and revolutionary applications of this laser-cooling technique. It really represents kind of a brave new world for what we can do.

Interviewer: Adam Levy

What’s your ultimate hope for, I guess, the outcome for all this antimatter research?

Interviewee: Jeffrey Hangst

I’m an experimentalist. I don’t have hope. I just measure. I hope to find the truth, let’s put it that way, right? So, we’d like to get to the same types of precision that one has with matter. That’s when you can say, ‘Okay, we’ve done the best job we can. We’ve done as good as the matter guys. Are these things still the same?

Interviewer: Adam Levy

Well, maybe a better question then is how does it feel to measure what you’re now able to measure?

Interviewee: Jeffrey Hangst

Well, this was my entire career. I started out when there was no antihydrogen. We didn’t know how to make it. We didn’t know how to trap it if we made it, and if we trapped it, we didn’t know how to measure. There really was nothing when I started, and a lot of people were very, very sceptical that this kind of thing would ever be feasible. Now, we’re trapping thousands of anti-hydrogen atoms at a time, we can hold them for unlimited amounts of time as far as the experiment is concerned, and there doesn’t seem to be any fundamental limitation to what we can achieve. So, yeah, this is as good as it gets in a career in physics, I think, when you start with something and the field evolves to a very mature state like this, so we’re very, very happy.

Host: Benjamin Thompson

That was Jeffrey Hangst, spokesperson of the ALPHA antimatter experiment at CERN and he’s from Aarhus University in Denmark as well. To find out more about cooling antimatter, be sure to check out the paper, and we’ll put a link to that in the show notes.

Host: Nick Petrić Howe

Coming up, I’ve been finding out about the economic costs of invasive alien species. Right now, though, it’s time for this week’s Research Highlights, read by Dan Fox.

[Jingle]

Dan Fox

Lightning is striking the high north nearly ten times as often as it did a decade ago, increasing the risk of wildfires in the rapidly warming Arctic. To understand whether lightning was becoming more frequent in the Arctic, a team of researchers mapped lightning strikes recorded worldwide by a network of ground-based sensors. Normally, lightning is less common in cold regions, but the team found that the number of summer-time lightning strikes above a latitude of 65° north had increased from around 35,000 in 2010 to 250,000 in 2020, with most of these strikes happening in Arctic Siberia. They conclude that rising temperatures in the Arctic seem to favour the formation of convective storm clouds, increasing the chances of fires and lightning strikes on ships in Arctic waters. If that paper strikes your fancy, read it in full at Geophysical Research Letters.

[Jingle]

Dan Fox

A breed of rabbit that walks on its front legs has revealed the genetic secrets behind hopping. The sauteur d’Alfort is a rare breed of rabbit that walks balanced on its front paws, with its hind legs in the air. To understand why these bunnies can’t hop, researchers bred a

sauteur d’Alfort with a standard rabbit that can jump, and sequenced the genomes of the pair’s 52 grandchildren. The researchers found that the descendant baby rabbits that couldn’t hop had a single mutation in both copies of a gene called RORB. They also had fewer neurons expressing the protein RORB in their spinal cords, which probably interfered with the movement of their hind limbs. Previous studies had shown that mice with RORB mutations waddled, suggesting that RORB is essential for normal spinal cord development and movement in animals. Hop or handstand over to PLOS Genetics to read that research in full.

[Jingle]

Interviewer: Nick Petrić Howe

Alien invasions happen on Earth surprisingly frequently.

Host: Benjamin Thompson

Nick, I knew it. All that time spent watching The X-Files re-runs and those hours spent watching those YouTube videos – the truth is out there, man.

Interviewer: Nick Petrić Howe

Laughs. The truth may well be out there, but I think you’ve actually caught onto my tricky bait that I left for you. I wasn’t talking about the aliens you might think of from outer space. I’m actually talking about alien invasive species.

Host: Benjamin Thompson

I mean, I’m disappointed but, okay, keep going. What have we got here then? What have you got for us this week?

Interviewer: Nick Petrić Howe

Well, these sort of biological invasions are where organisms end up in a location that they don’t really belong and then they can cause damage to the environment and the people who live there. This can result in a whole host of problems, and they are actually the second leading cause of biodiversity loss and as a result, they also end up costing a lot of money. There have been many estimations over the years as to how much this might be, but this week in Nature, a paper is compiling all these estimations over the past 50 years to try and understand the global cost. But why focus on the money and not the environmental impacts? I caught up with one of the authors, Franck Courchamp, to find out more about the study.

Interviewee: Franck Courchamp

If you talk about money then the politicians are going to understand. So, if you talk about a metric that is common for all different types of impacts that touch human activities then it’s much easier to convey a message to decision makers, for example.

Interviewer: Nick Petrić Howe

And that message is, ‘This is how much it’s costing,’ so I guess the question is how much are these sorts of invasions costing the world?

Interviewee: Franck Courchamp

The difficulty we had first was to try to sum the different costs that we found. So, the idea was to review all the papers, all the studies that we could find and to compile that. So, we had to standardise everything before, and once we had devised a method to standardise all the costs, we could make this compilation and then we would could have a global cost. So, the global cost is really enormous. In terms of billions, it’s 1,300 in the last 50 years, and on average per year it’s several dozen billions. And in the end, in 2017, the last year for which we have an estimate, it’s over US$ 160 billion.

Interviewer: Nick Petrić Howe

One of the things that was striking to me when I was reading the paper is that this seems to be going up all the time. So, you started looking at this dataset from 1970, and then I think you wrote in the paper that there was a threefold increase in the costs per decade. I was just wondering what’s sort of driving this increase in the costs?

Interviewee: Franck Courchamp

There are several things. First, obviously, is the increase in the number of records that are made and the number of studies that are made, but also because there are an increasing number of invasions. So, there are studies that show there is an exponential increase of biological invasions in the world, and we also show parallel exponential increase of the costs. So, mostly, we think it’s the increase of the biological invasions and the number of invasive species as global trade is increasing but also as climate change is opening new territories to invasive species, and third, because the costs themselves may be increasing as the invasions progress.

Interviewer: Nick Petrić Howe

I guess one of the key things and something you talked about at the start is making this apparent to people who make policy and things like that is are the costs that we’re seeing from these invasions, are they greater than the costs of, say, prevention or management of these species?

Interviewee: Franck Courchamp

The costs that we called the damages and the losses, for example the damages to infrastructure, the losses of agricultural yield or tourist revenue, those are one or two orders or magnitude higher than the cost of prevention, and when I say prevention, I should say management because management includes also the control when you try to mitigate the impact of a species or when you try to control it or to prevent its spread. The management is mostly post-invasion management, so reactive management, and the proactive parts, the prevention part, which is the cheapest, is also the one where unfortunately people invest the least. So, it’s the other way around than it should be done. People should invest in proactive management before the invasion to prevent them so that no cost occurs, and if they fail that they should invest in management rather than suffer the damages and loss, which are 1-2 orders of magnitude higher than the management costs.

Interviewer: Nick Petrić Howe

And another thing that really struck me when I was reading the paper as well is you talked quite a bit about how some of these costs are actually underestimated. Why did you say that?

Interviewee: Franck Courchamp

So, there are five different reasons for which we have much underestimated value. The first one is that we used very conservative methodologies and that we kept only about half of the data that we had, the most robust ones, and if we had taken everything, we would have had something like four times the final estimation. The second one is that there are a lot of costs that are not identified. For example, there are a lot of species for which the costs are not recorded as invasive species and one good example is rodents. When you have rats that make agricultural losses, sometimes you have studies that give the costs but they are not said as being invasive and so we don’t have the costs for that. Over 90% of invasive species have no costs recorded at all. There are biases geographically. A lot of different regions of the world have no costs at all, so we could not estimate those costs. And finally, there are some impacts that it’s difficult to monetise. For example, what is the value of pollination on an ecosystem, and if you have an invader that reduces the pollination, it’s difficult to know how much that costs really to the agriculture afterwards. For these five reasons, the costs that we provide are really the tip of the iceberg.

Interviewer: Nick Petrić Howe

And I was just thinking in the context of this year there is the UN’s COP-15, the conference of parties about biodiversity, is there anything there you’d like to see from policymakers in regards to this?

Interviewee: Franck Courchamp

Yeah, I think it would be really important for policymakers to realise that even though it’s always difficult to put money on the table for prevention and even though for global trade, for example, there can be some hindrances that would perhaps lower the income of some people who benefit from global trade, globally the amounts that we lose as a society due to invasions are so high that it is really worth putting this money on the table to try to prevent them.

Interviewer: Nick Petrić Howe

That was Franck Courchamp from Paris-Saclay University. For more on the costs of invasion, be sure to check out Franck’s paper in the show notes.

Host: Benjamin Thompson

Finally on the show, it’s time for the weekly Briefing chat where we discuss a couple of articles that have been highlighted in the Nature Briefing. Nick, what’s caught your eye this week?

Host: Nick Petrić Howe

Well, I was reading an article in the Financial Times that’s about a really big boat that you probably have heard of.

Host: Benjamin Thompson

Yeah, I’m guessing this is the boat in the Suez that kind of, well, got stuck, right? I mean, it’s massive, right? I heard some figures. It’s like 400 metres long. It’s an enormous thing.

Host: Nick Petrić Howe

Yeah, this is the very enormous Ever Given which, last week on Wednesday, ended up blocking the Suez Canal and causing a big disruption to trade. But that’s not actually what this article is about. This article is more looking at the physics about how this might actually have happened, and you might have heard that wind was the reason that the boat got stuck. But actually, it seems that it might be a bit more complicated than that.

Host: Benjamin Thompson

Right, I mean, I guess there’s a whole sort of combination of factors, right, so wind, as you say, the angle that the ship was moving maybe, and a bunch of other stuff too, right?

Host: Nick Petrić Howe

Yeah, and what this article really looks at are the hydrodynamics, so the physics of the water beneath the ship, and how that might have affected it and caused it to get stuck in the canal. So, the first thing to say is when you drive a boat, it’s not really like driving a car or riding a bike or something like that. There, you just sort of steer where you want to go and you sort of go there because you attach to the road. Whereas on a boat, you’ve got the water in the way and water can be, well, water is tricky, I think is probably underselling it slightly. And so, what can happen is that water can be displaced by ships, and that is something that happens in the ocean and is absolutely fine – there’s plenty of places for the water to go. But in the Suez, it’s quite a shallow canal and so because the water doesn’t have places to go, it can cause a lot of problems. And in the case of the Ever Given, the ship that got stuck, what the researcher that they spoke to in the article, who’s an expert on hydrodynamics, thinks might have happened is that it got a bit too close to the bank and ended up getting caught in a spin, and how that happens is sort of slightly complicated but I’ll go into if you’re interested, Ben?

Host: Benjamin Thompson

Yeah, absolutely, I mean, yeah, as you say, this canal is very much a defined channel and it’s difficult to displace water very, very far, so what’s the researcher found then?

Host: Nick Petrić Howe

What I will say, they’ve done this mainly by looking at videos and they’ve also done experiments with like model ships and things like that, but they think it got caught up in a well-known phenomenon called the bank effect. And to explain the bank effect, it’s worth explaining like how water is displaces by ships normally. So, in shallow water, a ship will be going along and if it’s a very big and very heavy ship like the Ever Given was, it will be pushing that water down, and if it pushes that water down, it causes the water to speed up and generates a small vacuum, which ends up making the back of the boat sort of sink in and the front of the boat sort of stick out. Now, that’s fine and dandy, but if you are to get too close to the bank then you get caught up in the bank effect, and what can happen then is this same thing happens but because you’re close to the bank, you end up sort of getting sucked closer to the bank and then you can end up in a spin, especially because this happens more at the back of the ship than the front, so the back ends up spinning there, and that’s what this researcher thinks has happened. So, there were winds, it was very windy, and it looks like the Ever Given was trying to steer to compensate for that, but then the researcher thinks that the winds actually lulled for a second and the boat was oversteering and when that happened it got too close to the bank and then got caught up in this effect and ended up spinning and getting wedged inside the canal.

Host: Benjamin Thompson

Yeah, I mean, I guess that kind of makes sense, right? It really was wedged in a diagonal so it’s again, this combination of factors that potentially has led to this situation which went on for several days, and I think at the time of recording it’s only just be released. So, that might be what went on then, Nick. I mean, can we treat this as a learning exercise in some way? Is this sort of knowledge maybe going to help avoid this kind of situation happening in the future?

Host: Nick Petrić Howe

Yeah, I think so. So, what the researcher emphasised is that we have been building boats bigger and bigger and bigger and we’ve been doing that faster than the research can sort of keep up. We have good understanding of how really big boats operate in the ocean and we’re able to build them large because we understand the forces working on them but when it comes to shallow water, we don’t actually know that much, and that’s going to be problematic for places like the Suez and the Panama Canal, where a lot of trade goes through and they’re actually quite shallow waters. And the thing is, these things are only going to get bigger and wider and have more and more containers on them, so it’s worth using this as a bit of a learning exercise so we can better understand how this might affect boats in the future and how we can maybe prevent it from happening.

Host: Benjamin Thompson

Maybe we need to misquote the movie Jaws then and say, ‘We’re going to need a smaller boat.’

Host: Nick Petrić Howe

Laughs. Quite possibly. What have you found this week, Ben?

Host: Benjamin Thompson

Well, Nick, let’s stick in the ocean, but this couldn’t be more of a different story to be honest with you and it was reported in Science, and it’s about the sleep patterns of octopuses.

Host: Nick Petrić Howe

Oh right, I think I actually saw some pictures of this on social media with octopuses glowing different colours. Is that was this story is about?

Host: Benjamin Thompson

That is absolutely right, Nick. There is an amazing video associated with this research, and check out the show notes for a link where you can find the article to watch it. And actually, that video is one of the sleep states for an octopus. But let’s back it up a little bit, right. So, in this case, it’s a team of researchers in Brazil who were looking at four octopuses asleep in a tank to see what was going on with them when they were asleep.

Host: Nick Petrić Howe

Alright, so they were looking at them when they were asleep. I have trouble sometimes telling when people are asleep, so how can you tell when an octopus is asleep?

Host: Benjamin Thompson

That is an absolutely fantastic question, Nick, and in this case the answer is showing a video of a crab or hit its tank very gently with a rubber mallet, and if it moves or has a little look then you can say that it’s awake. So, when you’re convinced that it’s asleep, you can see what’s going on, and what they’ve shown in this case is kind of two states of sleep. Now, there’s this sort of quiet sleep stage and the octopuses are kind of quite pale, their pupils are reduced to kind of slits and they’re mostly pretty still, maybe a little bit of waving of their arms, but pretty much they’re not doing very much. But then there’s this active sleep which we talked about, which you saw the video of, when they’re skin gets suddenly darker and stiffer, their eyes start moving about and their muscles twitch and all the rest of it, and this state lasts about 40 seconds, so I understand, and the cycle from this quiet state to this active state repeats every 30-40 minutes.

Host: Nick Petrić Howe

Right, so in humans we have a few different stages of sleep. We’ve got like REM and light sleep and things like that. Is it a similar thing with these octopuses? Are they dreaming or something like that?

Host: Benjamin Thompson

Yeah, you’re absolutely right, Nick, and there is a few bits to unpick there. So, yes, in humans this REM, this rapid eye movement sleep, is when we dream and this other kind of more stable sort of pattern is when electrical activity in our brains stabilises a bit. But whether we can compare a human and an octopus I think it’s quite difficult and the researchers have been quite careful in this instance because there’s the small matter of 500 million years of evolution between us, and human brains and octopus brains are very, very different things. But what’s thought that maybe is going on is that, well, octopuses are really smart, right, as we know, so maybe this kind of active sleep state is helping them when they’re learning stuff and helping them remember it, but to test whether that’s true and to answer the question of are they actually dreaming, well, it’s going to be really, really hard. It’s going to require electrodes stuck to their heads, that sort of thing, and octopuses are quite tricksy, so I think the researchers are worried they would just pull them off. So, ultimately, it’s going to be a difficult one to find out, but it’s interesting though that they have shown in another animal that there are these kind of different sleep cycles now, and that adds to mammals and birds. I mean, I’ve seen some videos of ostriches having these kind of sleep cycles and maybe some reptiles as well. So, an interesting one to look out for in the future.

Host: Nick Petrić Howe

That’s certainly one to keep an eye on. It sounds absolutely fascinating and I do recommend watching the video because the colour changes are very, very cool. But thanks for chatting to me, Ben, and listeners, if you’re interested in more stories like this but instead as an email then make sure you check out the Nature Briefing. We’ll put a link in the show notes where you can sign up.

Host: Benjamin Thompson

That’s all for this edition of the Nature Podcast. No show from us next week, but we’ll be back in a couple of weeks in all the usual places. In the meantime, you can reach out to us on Twitter – we’re @NaturePodcast – or you can send us an email – we’re podcast@nature.com. I’m Benjamin Thompson.

Host: Nick Petrić Howe

And I’m Nick Petrić Howe. Thanks for listening.

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