NATURE PODCAST

Superconductivity gets heated

A high pressure experiment reveals the world’s first room-temperature superconductor, and a method to target ecosystem restoration.

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Hear all the latest from the world of science, brought to you by Nick Howe and Shamini Bundell.

In this episode:

00:44 Room-temperature superconductivity

For decades, scientists have been searching for a material that superconducts at room temperature. This week, researchers show a material that appears to do so, but only under pressures close to those at the centre of the planet. Research Article: Snider et al.; News: First room-temperature superconductor puzzles physicists

08:26 Coronapod

The Coronapod team revisit mask-use. Does public use really control the virus? And how much evidence is enough to turn the tide on this ongoing debate? News Feature: Face masks: what the data say

19:37 Research Highlights

A new method provides 3D printed materials with some flexibility, and why an honest post to Facebook may do you some good. Research Highlight: A promising 3D-printing method gets flexible; Research Highlight: Why Facebook users might want to show their true colours

22:11 The best way to restore ecosystems

Restoring degraded or human-utilised landscapes could help fight climate change and protect biodiversity. However, there are multiple costs and benefits that need to be balanced. Researchers hope a newly developed algorithm will help harmonise these factors and show the best locations to target restoration. Research Article: Strassburg et al.; News and Views: Prioritizing where to restore Earth’s ecosystems

28:40 Briefing Chat

We discuss some highlights from the Nature Briefing. This time, a 44 year speed record for solving a maths problem is beaten… just, and an ancient set of tracks show a mysterious journey. Quanta: Computer Scientists Break Traveling Salesperson Record; The Conversation: Fossil footprints: the fascinating story behind the longest known prehistoric journey

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Transcript

Hear all the latest from the world of science, brought to you by Nick Howe and Shamini Bundell.

Host: Shamini Bundell

Welcome back to the Nature Podcast. This week, making room-temperature superconductors…

Host: Nick Howe

And a method to target ecosystem restoration. I’m Nick Howe.

Host: Shamini Bundell

And I’m Shamini Bundell.

[Jingle]

Host: Shamini Bundell

First up on the show this week, reporter Lizzie Gibney has been finding out why the search for the elusive room-temperature superconductor may finally be over.

Interviewer: Lizzie Gibney

Superconductors are pretty special. Discovered at the beginning of the twentieth century, they’re materials that can conduct electricity with zero resistance. Superconductors already make powerful electromagnets, with uses from steering particles around colliders to levitating a maglev train. But getting materials into this extraordinary state isn't easy, as Ranga Dias from the University of Rochester in the US explains.

Interviewee: Ranga Dias

So, the issue is that, yeah, all these superconducting properties that we have seen have happened at normally low temperatures. And then all these years, last century, we were trying hard, how we can bring this temperature all the way up to room temperature.

Interviewer: Lizzie Gibney

Because materials usually need to be cooled to close to absolute zero before they become superconductors, that seriously limits their uses. So, finding one that superconducts at everyday temperatures would cause a technological revolution, allowing for the creation of things like uber-efficient power lines and much faster computers. And there's no theoretical reason why, in the right material, room-temperature superconductivity can't exist. So, physicists have spent decades hunting it down, continually tweaking materials to push up that magic temperature at which they see resistance disappear. But none have quite reached room temperature until, it seems, now. This week, Ranga and his colleagues have a paper out in Nature, claiming to have found a material that superconductors at an almost barmy 15 degrees Celsius. Although, there is a catch, as his method involves compressing hydrogen to 2.6 million atmospheres – not far off the pressure at the centre of the planet. Pressure radically changes the material and the ways in which its atoms bond, and at super high pressure, hydrogen – the lightest element in the Universe – should form a metal. Back in the 1960s, a theorist hypothesised that in metallic hydrogen, vibrations within its lattice of atoms would throw together pairs of electrons in such a strong way that they travel with zero resistance, even at room temperature. But making metallic hydrogen requires truly planet-crushing pressures that are not easy to achieve. For the last few decades, teams around the world, and now including Ranga’s, have played around with different forms of hydrogen, trying to find one that might superconduct at lower pressures.

Interviewee: Ranga Dias

We were thinking, how we can bring the pressure down so that hydrogen needs to be metal but keeping the same superconducting properties? Instead of mechanically pressing hydrogen, can we chemically compress? So, the carbon and sulfur are the best candidates for this kind of idea.

Interviewer: Lizzie Gibney

The team created crystals of hydrogen, sulfur and carbon. The idea was that the sulfur and carbon atoms would compress the lattice of hydrogen from the inside, which decreased the external pressure required to crush them into a superconducting state. However, the pressure was still pretty high.

Interviewee: Ranga Dias

It's 2.6 million atmospheres, so a really high pressure. Just to give you an idea, so the pressure of the centre of Earth is 3.6 million atmospheres. For the metallic hydrogen, it’s 5 million atmospheres. So, compared to that, it's like half of that. So, we will manage to bring it down half of that pressure.

Interviewer: Lizzie Gibney

And how do you generate this vast pressure? Well, the technology is, in theory, pretty simple. They use a pair of small but super hard anvil-shaped diamonds to crush a tiny sample.

Interviewee: Ranga Dias

We have a small device. You have an allen key and your screws, and you just tighten those screws. Sometimes, people think that when we generate these high pressures we have like a big device that can do it, but actually you can put it in your hand.

Interviewer: Lizzie Gibney

When Ranga used this setup to squeeze his crystals, he saw their electrical resistance change as he increased the pressure.

Interviewee: Ranga Dias

We kept going up in pressure. We were like okay, let's squeeze further, and that's where we saw this dramatic change. It kept going up and up and all the way to 15 degrees Celsius.

Interviewer: Lizzie Gibney

At a pressure of around 267 gigapascals, or 2.6 million atmospheres, Ranga’s crystals showed all the hallmarks of superconductivity and, at 15 degrees Celsius, a record high temperature, and the first demonstrated room-temperature superconductor. But testing the properties of materials under these extreme conditions to make sure you really have seen superconductivity is pretty challenging. My fellow physics reporter, Davide Castelvecchi, has been talking to researchers around the world about what they make of Ranga’s claim.

Davide Castelvecchi

Many of the experts I've talked to seem excited, and they find the evidence rather convincing. One called it a landmark achievement. Now, obviously, all of them stress that this is just a first report and, of course, there will need to be follow-up experiments and other teams will have to confirm the result.

Interviewer: Lizzie Gibney

But although the data may be convincing, there's a lot more work to be done before this discovery can become really useful. The problem is that Ranga and his colleagues were unable to probe their crystal to find out exactly what its atomic structure is because the common techniques to do that just don't work so well on their sample of hydrogen-rich material at high pressure. Davide says that theorists and computational chemists need to know the structure so that they can play with the material, simulate it, and predict how tweaking it will affect its properties. And that is crucial for the next step – finding new materials that are superconducting at even lower pressures or that stay stable even once the pressure is removed.

Davide Castelvecchi

Once you know that a certain structure works at a certain pressure, you could, in principle, find other ways to create it that don't involve high pressure. For example, in nature, diamond forms down deep in the Earth's mantle at very high pressures, but then we also know how to synthesise it in a vacuum, in a lab, without high pressures. So, ultimately, you might be able to get to materials that could remain stable and superconducting even when you lower the pressure. Obviously, researchers want materials that can work outside of the lab and can lead to new technologies.

Interviewer: Lizzie Gibney

Ranga agrees that his hydrogen, carbon and sulfur mix is not going to be a very practical superconductor in itself. But he hopes it's an important milestone because for decades, it looked like extreme cold was a prerequisite for superconductivity. Now, we know that's not true.

Interviewee: Ranga Dias

So, there were times that we were thinking okay, a room-temperature superconductor is not even possible. We've been trying for a century. But at least now we know, yeah, it is possible. We can have room-temperature superconductors. If you understand the mechanism, then we can really design a material with these same properties at much lower pressures. It doesn't have to be carbon and sulfur and hydrogen. It could be something totally different.

Interviewer: Lizzie Gibney

Reaching this ultimate goal – a room-temperature and ambient-pressure superconductor –will require a lot more work. But if their result stands up, Ranga’s team could have provided the key to finding the crucial combination of elements and conditions that would create it, and given a well-needed boost to a decade's long hunt.

Host: Shamini Bundell

That was Lizzie Gibney. You also heard from Nature's Davide Castelvecchi, and Ranga Dias from the University of Rochester in the US. To read Ranga’s paper, look out for a link in the show notes.

Host: Nick Howe

Next up, it’s time for our weekly update on coronavirus with Coronapod.

Host: Benjamin Thompson

Thanks, Nick. Yes, that's right. I'm Benjamin Thompson, and I'm joined on Coronapod this week by Noah Baker and Brendan Maher. Hello to you both.

Brendan Maher

Howdy.

Noah Baker

Hi there.

Host: Benjamin Thompson

Brendan, listeners might not have heard your voice on the show before. What do you do here at Nature?

Brendan Maher

Well, I'm a news features editor specialising mostly in long-form biology stories.

Host: Benjamin Thompson

Which is the ideal fit for what we're going to talk about today, and we're going to revisit a topic we've not looked at for a while, but it does still seem to be debated a lot, and that is masks and the evidence of whether their use by the public is helping to control the spread of coronavirus or not. Now, the last time we touched on this, Noah, was, goodness, way back in the start of the summer, I think, and there was lots of conflicting information going on which was confusing a lot of people.

Noah Baker

It's such a weird one this, right, because, on the one hand, if you think about this with just a purely sort of common-sense hat and don't think about it in terms of any kind of empirical data, it seems like, yeah, that seems like a sensible thing, right? Wearing something over your face that would stop things going out of your mouth or out of your nose or going into your mouth or into your nose, when you're talking about a respiratory condition, that makes logical sense. Of course, a mask is going to be helpful. And yet, this has been something that has been hotly debated by many people, and it's actually something that, for quite some time, there wasn't very much data to actually confirm the sort of common-sense approach. But as time has gone on, that data has grown and that's why we are revisiting it now, and I'm sure Brendan can tell us a little bit more about the latest data on how effective a mask could be.

Brendan Maher

Yes, well, I had one of my favourite freelancers, Lynne Peeples, who's got a lot of experience with biostatistics, look into this. Now, she's done some other stories for us on very controversial topics like gun violence and police brutality, so this was not really much of a stretch for her to wade into something that was both complex and also quite contentious. I would say, in even assigning the story, I was wondering, why are we still asking this question, like you say, Noah. I mean, it just seems like a sort of common-sense precaution that you could just take. But indeed, there's a lot of people still kind of debating it based on arguments generally to do with personal freedoms. There's some people who claim that there are potentially some safety issues associated with wearing masks and kind of things like that. But really, I'd say the balance of the data and the balance of the experts that she talks to really come down on a consensus that they appear to be saving lives when you wear them properly. And in conjunction with other measures, such as social distancing, things like that, that they are helping.

Noah Baker

Yeah, so there's a load of different ways where people can kind of question why masks might not be effective, which is kind of the thing that has caused the debate. There’s a common-sense idea that they might, but then there might be reasons they weren't. I guess I'm interested in what research has been done since the beginning of this pandemic to try to get to the bottom of what masks are actually doing.

Brendan Maher

So, you can look at sort of what we might call a natural experiment, where a certain jurisdiction has imposed mask regulations and see are they, in fact, being healthier? A couple of well publicised case studies looking at some hairdressers in the Midwestern United States who were masking during work but not masking at home, they were both infected with coronavirus and spread the virus to their families but not to people that they were working with in their salons. So, that would seem to indicate that masks are doing something useful there. But there's just no way to control for behaviour and really understand kind of what's going on at a more minute level. To get at more controlled experiments, you can look at animal studies, and people have done that too. They've put, I believe, hamsters in cages separated by mask material facing both ways, sometimes with the blue side out, sometimes with the blue side in, and they do find that indeed, the infections seem to spread less when there is mask material between cages. Then you can really ramp up to kind of what is sort of the gold standard of evidence for an intervention, and that's a clinical trial. Now, there's only two clinical trials that we’re aware of. Both were started in Denmark. One is on people in Denmark, and we've still not seen the results of that trial. It has concluded though. There's another trial that's ongoing in Guinea Bissau that Lynne talks about quite a bit. They're talking about tens of thousands of people, distributing masks to half of them and not distributing masks to the other half, but following up with them and seeing how they're doing, and this would be potentially one of the strongest lines of evidence that would support or not support wearing masks.

Host: Benjamin Thompson

Experiments like this then seem super important, but what about the granular level? I mean, I wear a mask when I go to the shops. I'm sure you both do as well. But I mean, the likelihood is they're going to be totally different, right? So, what happens to me and what happens to you is going to be very, very difficult to compare those apples with those oranges.

Brendan Maher

I think in in a controlled experiment like that and a big trial, you can really at least start to get at what all those variables are because you're specifically trying to look at them and you have a designed endpoint that you're trying to understand. But as you're saying, kind of with the observational studies, person A wore a mask, person B didn't, and you're kind of looking at infection rates after the fact. That's much more difficult to really piece together a clear story of what's happening.

Noah Baker

There are just so many variables. Right now, I'm wearing a kind of a surgical mask. It's actually not what I wear normally. Normally, I wear like a two-layered fabric mask which I made, based on some specifications I got from a paper out of Cornell that was trying to look into ways you could make a homemade mask that might be effective, and that was purely just because I didn't want to be using disposable things if possible. But it is very, very hard to know. What one person calls a mask could be just like a bandana tied around their face and what someone else calls a mask could be one of these sort of verified, highly tested, understood N95 pieces of equipment, and you can't just say a mask works when you might mean one of those two things because they might work in very different ways.

Brendan Maher

Right, and that's also evidence that Lynne tried to kind of pick through. There's a lot of studies, often run by physicists and others, that have really good methods for visualising the amount of particles that are coming out of a person's mouth while they're speaking and trying to get a sense of what mask materials work the best. And they show, somewhat reassuringly, that bi-layer mask, especially if it's got two different kinds of fabric, can really cut down on the amount of aerosols that someone's spitting out while they're talking or breathing. And from what we understand, that seems to be a pretty predominant way that the virus is being spread. So, again, these are just more lines of evidence that are pointing to that uber conclusion that these masks seem to be doing something. They seem to be helping.

Noah Baker

Yeah, I remember – it's a very odd and specific memory to have, actually – but I was reporting for a story about astrophysics on the East Coast many years ago, and while I was there, I happened to go and visit MIT and I visited a researcher called Lydia Bourouiba. She's a mathematician and she looks at the physics of sneezes. And so, she specifically made a load of people sneeze and tracked all of the sort of aerosols that came out – I made a video about it – and I remember her saying at the time, ‘When it comes to try to come up with any recommendations for respiratory conditions, we really don't have clear understandings of how these things work, and our research is showing that maybe things could spread in droplets or in aerosolised particles much further than we expect.’ And I remember saying to her, ‘I’m surprised people don't know more about this,’ and she was like, ‘I know, people don't but, one day, people will care a lot about that,’ and now I find myself sitting here discussing how effective masks could be in a pandemic and thinking, ‘Hmm, maybe I should have made more than one video about Lydia Bourouiba’s work,’ because it was fascinating. It was also gross, by the way, because there was a lot of high-speed footage of like disgusting mucus coming out of people's mouths.

Brendan Maher

There's just not been a whole lot of study thrown at respiratory infections. I mean, we know a lot about influenza, but we don't really know entirely how it is spread from person to person. There's sort of long and protracted debates about what really constitutes an aerosol, how small a particle needs to be to be considered an aerosol, how long it would stay in the air and whether or not viruses can survive in the air for extended periods of time. We know that measles is much more transmissible and can hang around in the air for hours and can spread to every corner of a room with very little help. Whereas, influenza does not seem to be as transmissible, but kind of any of the real fine grain details in between and sort of where coronavirus lies are just not greatly known.

Noah Baker

I think it's probably worth adding, I remember when we spoke about this before with Amy Maxmen, we discussed various pieces of research we knew about masks at the time, and one of the things she said is, in her opinion, masks would be useful, but is this pandemic going to rest on masks? Are masks is going to be the thing that define the pandemic? I think probably not, was her suggestion. And I think at this point, we're probably still thinking a similar thing. Even though masks might be useful, they're not the most important thing for all of this. Then we start thinking about testing and tracing, and there are other public health interventions which could potentially be more impactful than masks.

Brendan Maher

Well, I’d say the concentration is on masks. It's what you notice. Are they the end all be all? Absolutely not. I think you need other measures in place to keep people safe. But that consensus seems to remain that people think that this is working. This is helping.

Host: Benjamin Thompson

Even if we get to a stage where this research says 100% guaranteed, wearing a mask of whatever kind will lessen your chances of infecting someone else or perhaps being infected yourself, do we get a sense that that will make a blind bit of difference? I mean, given the way that things are going at the moment?

Brendan Maher

Hard to say. In the United States, there seems to be a lot of resistance to any sort of scientific advice, regardless of the amount of data that's stood behind it, and there's lots of data being generated that may countervail this and there's lots of experts speaking that don't believe that masks are working the way the majority of experts do believe they are. And it's just created this haze of misinformation and doubt that's just been spreading around for months that is really dispiriting to watch. As one of the sources in Lynne's story mentioned, everybody is looking at this evidence, but they're looking at through the lens of what they want to believe and, ultimately, that's what they take away from it.

Host: Benjamin Thompson

Well, sadly, in this case, a debate that’s seemingly set to run and run. Brendan, I hope you'll join us in future when we get some more of this data and we can maybe uncover more about what's really going on. Brendan, and Noah, thank you so much for joining me today.

Brendan Maher

Thanks so much for having me.

Noah Baker

Thanks, Ben.

Host: Shamini Bundell

More from the Coronapod team next time. Coming up in this week's show, researchers have been working out which areas to focus on when restoring ecosystems. First, though, it's the Research Highlights, read by Dan Fox.

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Dan Fox

New molecular building blocks could make 3D printers more versatile by allowing them to make objects that are either incredibly bendy and stretchy, or stiff and tough. Volumetric additive manufacturing, or VAM, is a method of 3D printing that produces objects by projecting multiple beams of light into a spinning vial of resin, solidifying the desired shape within minutes. So far, this technique has only worked with resins that harden into objects as brittle as glass. Now, a team of researchers have identified three suitable molecular building blocks and have combined them into resins. By varying the ratio of these molecules in the resins, the team can create objects with a vast range of material properties. Some printed objects could stretch to more than four times their length before breaking, while others were stronger than the most high-performing engineering plastics used in planes and cars. 2D print that research and read it in full from Advanced Materials.

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Dan Fox

When was the last time you updated your Facebook status? Now, how honest were you? Because new research suggests that people who post more authentically to social media might be happier with their lives. A group of researchers collected around 10,000 questionnaires that respondents completed on Facebook, assessing their own personalities and life satisfaction. The team then compared these with the results from models developed to infer an individual's personality from their Facebook activity. Users whose self-assessed personality matched up well with their behaviour on the site – in other words, those who express themselves more authentically – expressed more life satisfaction than those whose self-description differed from their behaviour. So, does being authentic on social media make you happier or do happier people post more authentically? The authors asked a small cohort to spend a week posting authentically to social media and another week presenting a self-idealised version of themselves. Preliminary results from this suggest that authentic expression does improve mood. Post a status update if you enjoy reading that research in full at Nature Communications.

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Host: Nick Howe

Next year will mark the beginning of the United Nation’s Decade on Ecosystem Restoration. Many ambitious targets have been set, but these are usually measured by the total area restored. This week in Nature, researchers have come up with a different approach. They've developed a global analysis of the costs and benefits of restoration in different locations, which people can use to focus their efforts. Anand Jagatia reports.

Interviewer: Anand Jagatia

Ecosystem restoration is about regaining the ecological function of environments like landscapes, lakes and oceans. It can aim to reverse ecosystem degradation by removing pollution or invasive species, or it can target land that has been converted to agriculture, restoring it to its former state through interventions like planting trees. Ecosystem restoration has many benefits. It can conserve biodiversity by preventing species extinction and mitigate climate change by absorbing carbon dioxide from the atmosphere. But there are also costs to restoration, which include obvious things like labour and fertiliser, but also the opportunity cost of income that's lost by not using land for crops. Not only that, the benefits of restoration can often be in conflict with each other.

Interviewee: Bernardo Strassburg

There have been some proposals put forward in the last few years talking about planting trees, but if you're planting trees in areas that trees didn't belong originally, you're still getting benefits for carbon, but you'll be damaging biodiversity significantly.

Interviewer: Anand Jagatia

This is Bernardo Strassburg from the Pontifical Catholic University in Brazil, also founder of the International Institute for Sustainability.

Interviewee: Bernardo Strassburg

The benefits and the cost, they vary tremendously in space. So, it'd be areas that would be very important for carbon and the areas we have very low cost, and if you think of these objectives in isolation, then you're probably missing out what you should really be looking for, which is the areas that maximise the synergies and minimise the trade-offs.

Interviewer: Anand Jagatia

Bernardo and colleagues have developed an algorithm that can prioritise areas for restoration using data on the location of ecosystems, how much carbon they could absorb, the habitats they provide for vertebrates, as well as what the land is currently used for and how much it might cost to restore.

Interviewee: Bernardo Strassburg

I think there are three interesting aspects to what we have done. First, we develop an approach that is very flexible to the types of benefits and costs we went to include. It's very precise. We identify the optimal solution given the types of benefits and cost you would be aiming for. Third, the approach is able to measure the outcomes, the impacts, of each of these prioritisation areas.

Interviewer: Anand Jagatia

And when deciding which ecosystems to restore, the algorithm shows that the best strategy is to take all the potential benefits and costs into account.

Interviewee: Bernardo Strassburg

One of the most interesting things we found in this study is that if you prioritise for one objective only in isolation, for instance, biodiversity, you would achieve reasonable results for climate but that would be very expensive. If you aim for climate only, you get average results for biodiversity and it’s still very expensive. If you aim for reducing costs only, then you have very bad results and outcomes for both biodiversity and climate. What we found in what we call the multiple benefits solution is when you optimise for these three things at the same time, you achieve major increases in cost effectiveness of restoration, and you get very close to the best outcomes possible for biodiversity, climate and cost reduction at the same time.

Interviewer: Anand Jagatia

Prioritising restoration using this multiple benefits solution could potentially give some powerful outcomes.

Interviewee: Bernardo Strassburg

The outcomes are very, very impressive. They surprised even us. So, we found that, for instance, if we restore 30% of areas that have been converted, we could save from extinction up to 71% of the species currently committed to extinction. We would soak up from the atmosphere about half of all this huge increase since the Industrial Revolution, and we've got, at the same time, reducing costs by about 30%. It's the first study that covers the entire globe and all types of ecosystems. Previous analyses have been focused on forests. And what we found is that all ecosystem types have a role to play. Forests are obviously very important, but wetlands, for instance, on a per hectare basis, they're even more important for biodiversity conservation and climate change.

Interviewer: Anand Jagatia

But there are limitations to the model. For example, it doesn't consider the effects of climate change itself, how it might change the distribution of potentially suitable habitats for endangered species, or how current habitats may become degraded in the future. Bernardo is working on this though. So, could this approach be used in practice to help maximise the benefits of ecosystem restoration?

Interviewee: Bernardo Strassburg

We do hope so. We’re already applying in practice. We are guiding the Brazilian government. Nature-based solutions, for which restoration is a key element, it’s the most powerful one, can provide a massive contribution to combating global warming. It still receives much less media and financial attention than its proportion to the size of the solution. And at the same time as combating climate change, we have a very powerful tool to save life on Earth, and we can do both of these things in a cost-effective way for people and the planet.

Host: Nick Howe

That was Bernardo Strassburg from the Pontifical Catholic University in Brazil. To find out more about the algorithm he and his team developed to target restoration, you can check out the show notes, where there'll be a link to the paper.

Host: Shamini Bundell

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 hot in science this week?

Host: Nick Howe

Well, I've been reading about some researchers who have finally beaten an algorithm that has stood the test of time for 44 years, and I was reading about that in about that in Quanta Magazine.

Host: Shamini Bundell

And how exactly do you beat an algorithm?

Host: Nick Howe

Well, it's all about how efficient you can make it. So, to understand this, Shamini, I'm going to ask you to take on the role of a travelling salesperson. Can you do that for me?

Host: Shamini Bundell

Haha, yes, Nick, I can, and can I also interest you in these toilet brushes?

Host: Nick Howe

For the purposes of this, it doesn't actually matter what you're selling. But the idea is, you've got a few different cities that you want to visit because you are a travelling salesperson, and you want to go around and come back to where you started. And as this travelling salesperson, Shamini, what might you want to do in order to do that most efficiently?

Host: Shamini Bundell

Oh, I guess probably the least distance overall so that it's the quickest.

Host: Nick Howe

Exactly, and that will save you time and also money. So, this is called the travelling salesperson problem because scientists are very inventive, and basically, for a long time, researchers were trying to work out how you can algorithmically – so using computation –work out what is the quickest and shortest route to do something like this? And that's useful for a whole range of things from sort of DNA sequencing to actually making routes for people.

Host: Shamini Bundell

And presumably we're talking about problems that are sort of complex enough, like there are enough points on this map that you can't just try every single possible route and then pick whichever one that gives you the smallest number because there's too many options.

Host: Nick Howe

Yeah, so I mean, for this, you can use as many different cities as you can think of. So, the more cities you add to this, it goes up exponentially, the amount of complexity. So, if you visit two cities then that’s simple, you just go directly between them. Three cities, suddenly that’s a lot more complicated and also, it's complicated by the fact that there are different distances between them as well. So, it's not something that is easy to just brute force your way through and just be like, let's try all the different routes and just see which one is the shortest. So, what researchers did is, over many years, people tried to tackle this problem and finally, in 1976, a researcher came up with an algorithm, which was quite a simple one, that basically allowed you to get the best approximate solution. So, never the exact best solution, but the best approximate solution, that was only ever 50% longer than the actual optimal solution, and this has stood since 1976, so for 44 years.

Host: Shamini Bundell

Wait, 50% longer than the most efficient one? That's a lot. Doesn't seem that great. But okay, I will, accept that that was super impressive. So, you started off by saying some researchers have beaten the algorithm, but presumably not with the power of their brains. Presumably, they've designed another algorithm, a better algorithm?

Host: Nick Howe

Yeah, so it's a modification of the original algorithm, and the details of it are quite complex. But essentially, it comes down to not thinking of it as a map. So, actually, what they're doing is they’re designating different aspects of this as polynomials. So, for people who aren't familiar, a polynomial is where you have things like 3x^4 or something like that, so you have different variables that can represent different things. So, in this case, they could represent different distances between cities or they could represent how many different routes in and out of a city there were and things like that. And so, by simplifying in this way, researchers have managed to develop an algorithm that is 0.2 billionth of a trillionth of a percent better than the algorithm from 1976.

Host: Shamini Bundell

Oh, wow, wait, so this 1976 algorithm hasn't been beaten for however many years, and they're now they've got a, wait, did you say a 0.2% improvement?

Host: Nick Howe

0.2 billionth of a trillionth of a percent. So, a tiny, tiny, tiny percent.

Host: Shamini Bundell

So, it’s still basically the same? Wow, I'm less impressed now. Sorry. Sorry science.

Host: Nick Howe

It doesn't sound like much. But as I said, this algorithm has been unbeaten for 44 years. So, the fact that it was beaten at all shows that it's possible to beat it. And I think for many researchers, that will unlock almost a psychological block because a lot of people just won't even bother trying because it’s stood the test of time for so long. And now it's been shown that it's possible, then maybe there are other ways to do and maybe this polynomial method is one that will open up a bunch of new possibilities and allow researchers to improve it yet further. But we'll have to wait and see.

Host: Shamini Bundell

And then the significance of this is not just I think you mentioned for travelling sales people, but there's all sorts of genetic calculations and things like that that could be useful if we can get even more accurate.

Host: Nick Howe

Yeah, there were whole sorts of different things. So, a good example is if you have like a ride-sharing app, so like the Ubers and Lyfts of the world or something like that, and you're trying to decide where you want to go but also which cab is closest and that sort of thing. This can be really helpful for that. But because it's sort of like you could exchange cities for a whole range of different things and use it just to try and estimate the shortest route between any sorts of things. So, it's useful for a whole range of applications, and if it can be improved, the things that this previous algorithm is used for will also be improved.

Host: Shamini Bundell

Well, I shall wait to hear the next trillionth of a percent improvement that I'm sure we'll discuss on a future Briefing. So, the story I've been looking at today is also about a journey but a journey on foot and a journey made quite a long time ago, a particular journey which was made over 11,000 years ago.

Host: Nick Howe

Okay, so who was making this journey? What do we know about it?

Host: Shamini Bundell

Well, so, this is one of various footprint trackways that we found and, in particular, these are footprints made by humans. And these tracks were found in the White Sands National Park in New Mexico. So, what it is, is basically a surface, a huge, long, flat surface, that was mud and then has now been sort of hardened and preserved, preserving these amazing footprints. And all we have is footprints, but you can tell quite a few things about the person who might have made them and what they were doing at this time thousands of years ago.

Host: Nick Howe

Yeah, I mean, I'm guessing there's something else to this story because a human going for a walk 11,000 years ago doesn't sound particularly breaking. So, what was the story behind these footprints?

Host: Shamini Bundell

I cannot believe that you would say that. It is absolutely fascinating. So, the reason I love this story, and there's a paper and it's written up in The Conversation, and the reason I love it is actually because it is such a mystery. So, the main newsworthiness is that it's the longest known trackway of this kind. It goes over one and a half kilometres in a like practically dead straight line. Looking at the footprints, they can see that it was quite small, probably a woman, maybe like an adolescent male. They can tell from like the shape of the tracks, and how the foot has sort of landed, that the person was carrying something. There's a sort of characteristic outward rotation that your feet do when you're carrying a heavy load. And the clue as to what they were carrying – this is my favourite part of the story – is because every so often, you've got these sort of adult footprints going along and then a couple of times, you just get these two little small child footprints where this person was clearly put down the toddler that they were carrying, maybe to like shift position and stuff, and then picked them up again and carried on.

Host: Nick Howe

Wow, so they were taking this toddler quite a long distance. Do we know why? Were they running from something?

Host: Shamini Bundell

Well, they were going quite fast. So, again, they like to try to estimate the speed that the person was walking at, and they estimated that they were going around 1.7 metres per second, maybe more and apparently, a comfortable walking speed is like 1.2 or 1.5. So, someone like deliberately making quite a fast journey and by themselves as well. You've got this track outwards. You've also got some tracks of other creatures that sort of lived at this time. So, at one point, there's a track of a giant sloth that approached the tracks and then you can see had sort of like reared up maybe to like sniff the air and make sure there were no dangerous humans around before going back and sort of crossing over the tracks. You've got a mammoth track crossing over them as well. Then you've got a set of footprints coming back the same way, but without the child. So, what looks like the same outward footprints after the other animals have crossed over, coming back the same way again. And I just love the mystery of that, of trying to imagine what was going on in these people's lives so long ago.

Host: Nick Howe

So, they think it was the same person coming back without the child?

Host: Shamini Bundell

Yeah.

Host: Nick Howe

Wow, so yeah, it’s quite the journey to make and under mysterious circumstances. Does anyone have any theories?

Host: Shamini Bundell

Oh, lots of theories, but I think they're trying not to have too many theories. So, this article hypothesises that were they going to a particular village or community of people that they needed to maybe like return the child to? Maybe its mother was there or maybe it was ill and they had to go somewhere. Did something happen? The fact that they were walking through sort of slick mud, was there some sort of like horrible weather that made them like want to go really quickly? But there's no possible way to really tell.

Host: Nick Howe

Wow, so real mystery just in footprints. But I think it’s also time for us to make tracks, Shamini, because it’s the end of the Briefing chat. But thank you for talking to me and listeners, if you'd like to know more about the stories we discussed then make sure you check out the show notes. We'll put a link to all the articles we discussed. And if that's just wet your whistle for interesting science updates, then make sure you check out the Nature Briefing as well, where there's plenty more where that came from. We'll put a link of where to sign up in the show notes.

Host: Shamini Bundell

That's all for this week. But don't forget, you can get in touch with us either on Twitter – @NaturePodcast – or by email – podcast@nature.com. Send us a message and we might even read out on the show. You can also check out our YouTube channel. We had a video out last week about science under Trump and some of the things that he's done over the last four years that have influenced science. So, check that out and we'll put a link to that in the show notes. I'm Shamini Bundell.

Host: Nick Howe

And I'm Nick Howe. Thanks for listening.