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Interviewer: Adam Levy
Hello and welcome to this week’s Nature Podcastwhere we’ll be trying to demystify the complex subject of topology. My head hurts already in anticipation.
Interviewer: Shamini Bundell
Plus we’ll find out what determines how fast animals are.
Interviewer: Adam Levy
Oh yeah, what does determine how fast animals are?
Interviewer: Shamini Bundell
We’ll find out. This is the Nature Podcastfor July the 20th2017. I’m Shamini Bundell.
Interviewer: Adam Levy
And I’m Adam Levy.
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Interviewer: Adam Levy
One word in particular has been echoing around Naturetowers this week: topology. Topology is the mathematical study of shapes but it isn’t just a subject for pure mathematicians. It’s helping physicists understand bizarre behaviours in all sorts of materials. Last year’s Nobel Prize for Physics was awarded for work in this field and this week Natureis publishing two research papers and a feature on the subject. But what exactly is topology and why is it useful? The more I’ve been asking that question the more confused I’ve become. It turns out that I’m not the only one. Topology is a notoriously complex and difficult concept. To add to the confusion, physicists and mathematicians think about topology in very different ways. Even so, thinking in terms of abstract shapes hidden in some materials is helping physicists to describe new states of matter. So, we’re dedicating a good chunk of this week’s podcast to getting a handle on the topic of topology. To help me make sense of it all, I’m joined in the studio by not one but two physics geeks. Davide Castelvecchi has just written a feature on the topic so if he can’t help us, no-one can. Hello Davide.
Interviewee: Davide Castelvecchi
Hello.
Interviewer: Adam Levy
And to help explain we are also joined by physics reporter, Lizzie Gibney. Hi Lizzie.
Interviewee: Lizzie Gibney
Hi Adam.
Interviewer: Adam Levy
Lizzie, how confident are you feeling about explaining topology?
Interviewee: Lizzie Gibney
I think I would do an alright job of describing what we are talking about when it comes to the mathematical side of topology. I could also give some good examples as to where topology is relevant in physics. I would say the line between the two is a lot harder and the kind of thing that I’m very happy Davide has taken on in this feature.
Interviewer: Adam Levy
Davide is that the stuff that you were previously unsure of – the link between the maths and the physics – and was that where you had to brush up for writing this feature.
Interviewee: Davide Castelvecchi
Absolutely and I think brush up is a kind of understated way of putting it. It took several months of remedial lessons from our colleagues, the manuscript editors, not only of Naturebut all the Naturejournals that helped me understand and navigate this field. I think that maybe Lizzie remembers when the Nobel Prizes last year were announced, the terrified look in our faces we exchanged because it was a topic that obviously we had heard about and read about a lot. It’s one of the hottest trends in physics – these topological materials – and I had never really understood what that meant and so it was kind of the worst possible topic to have to explain on deadline, the day that Nobels were announced.
Interviewer: Adam Levy
And you had to write that together? How long did you have?
Interviewee: Lizzie Gibney
So, yeah, it’s annoying that every year that the Physics Nobel is announced on a Tuesday morning and we go to press at Tuesday lunchtime so we usually get about, I would say, about an hour and a half to write the piece and there’s about an hour and a half for it to be edited and sub-edited, and then go into print.
Interviewer: Adam Levy
To put that scramble into some context: I think this, for many people might have been the first time they heard about topology and well, this is what they would have heard if they were listening to the announcement…
Audio Clip: Physics Nobel Prize announcement
So I brought my lunch. Here you see, it’s a cinnamon bun. Here I have another thing: I have a bagel, okay. And here I have a pretzel. Now, for us these things are very different but if you are a topologist there is only one thing that is really interesting with these things: the number of holes.
Interviewer: Adam Levy
Davide, what did you make of this explanation?
Interviewee: Davide Castelvecchi
Well, it felt like they were waving their hands and not really… They were describing a topological idea that I was very familiar with. How that applied to states of matter was completely obscure.
Interviewer: Adam Levy
We should say that it wasn’t just hand-waving figuratively; he was literally waving his hands around while holding these objects in them. So now you’ve been given a few months to think about it, what would your explanation be for what the award was for?
Interviewee: Davide Castelvecchi
The Nobels rewarded the study of new and unexpected states of matter where the properties of the state of matter are determined by some topological effects. And the way that topology pops up is in these abstract spaces made of energy levels of the electrons in the material.
Interviewer: Adam Levy
So when we say topological effect, are we saying that these doughnuts and pretzels are somehow appearing in solid objects? What are we physically saying is going on?
Interviewee: Davide Castelvecchi
Absolutely there are doughnuts and pretzels in solid objects except that they are not physically in the object; they are in this abstract space made of energy levels…
Interviewee: Lizzie Gibney
… that describes the object,
Interviewer: Adam Levy
I think this is why this subject goes from being something I can think about quite easily, like a doughnut or a pretzel, to something more difficult because it is so close to being something tangible and then you say the words ‘it exists in an abstract space’.
Interviewee: Lizzie Gibney
When we talk about phases of matter or states of matter there are some where it’s very easy, like a solid, a crystal. You have this order which is in space. Everyone can see that. Everyone knows what’s going on. When you have something like a magnet it’s about the ordering of the spins of the atoms. You can’t see it but they have some kind of association and we call that a different type of phase: that’s magnetic. You have something like a liquid, or at least a quantum liquid, and it’s really not obvious – it looks like everything’s going everywhere. But actually you might have some order you can’t see in terms of, there might be order in the momentum in which all of these different particles are moving. So when I think about topological effects, topological order, it’s about some kind of property that, like the direction of spins in a magnet, unites a material. But it’s something that is very abstract which is kind of a hidden kind of order and then what’s interesting about it for physicists is that if you have this particular kind of order, it’s very useful because it’s very, very hard to change from that state to another one.
Interviewer: Adam Levy
When I was reading your feature, Davide, I found the example of the electron and the Möbius strip pretty intriguing. A Möbius strip, it’s like a ring made out of paper with a half twist in it so if you start on the outside of the ring, you go around once, you find yourself on the inside of the ring. Now what does that have to do with electrons?
Interviewee: Davide Castelvecchi
So the fact that when you take the spin of an electron and you make it go around a full circle, the electron doesn’t come back to the same state, and instead it has its wave function – this mathematical object that expresses its quantum state, becomes flipped and you have to rotate the electron all around once more to take it back to the original place and this is – there is actually topology in there in the quantum state of the electron. There is a little Möbius strip that does this and the idea is the quantum state gets flipped just the way that an ant crawling all around a Möbius strip finds itself upside down and then has to crawl around once more to find itself at the same place.
Interviewee: Lizzie Gibney
And the thing is when we’re talking about an electron, that’s a system physicists understand very well and can describe ad infinitum, but when we are talking about much bigger systems, then thinking about them in terms of their topology becomes very, very useful because it might not be as easy to describe as a single electron.
Interviewer: Adam Levy
So an example of a more complicated phenomenon that topology helps explain is topological insulators: materials that don’t conduct electricity except on their surface. How does topology end up being useful to describe materials like this? And is it to do with baked goods?
Interviewee: Lizzie Gibney
The one way in which I think the pretzels and the doughnuts were useful – or could have been useful if described a bit better – is, topologically speaking, a bowl is the same as a plate, so you can deform one into another. There are an awful lot of things about this system we just don’t care about. It’s actually a very simplistic way of describing it. There are a few key things that are important, that lots of others aren’t. So you can stretch to form it, twist it, but you cannot put a hole in it. That gives you a sense of when we are talking about some kind of topological phase. It takes an awful lot to change from one topological phase to another and what if you’re trying to store information, say, in that phase? That can be really useful because in that case you can do an awful lot to that system and you’re still not going to lose that information. That information is only lost, in this example, if you somehow manage to punch a hole through it.
Interviewer: Adam Levy
And is that robustness the only reason that physicists care about topology.
Interviewee: Lizzie Gibney
I wouldn’t say it’s the only reason. I’d say that’s the reason why there may be quite a few interesting applications of it.
Interviewer: Adam Levy
What do you think are the things to watch out for in topology? Either new applications that might come to fruition or whole new fundamental physics?
Interviewee: Davide Castelvecchi
Yeah , so what Lizzie was just describing about robustness of information, so this is one of the hottest, or most exciting potential applications, is the idea of quantum bits and the idea of building a quantum computer where you could run certain quantum algorithms that can do things that ordinary computers can’t do or can only do very slowly. There are multiple approaches to building a quantum computer but the biggest problem is that the information stored in these quantum bits or qubits is typically very fragile. And in principle these topological states could lead to building quantum computers that are easier or simpler to manage.
Interviewer: Adam Levy
There are two topology papers out this week by different groups. One is looking at an exotic material that looks like its breaking a conservation law of physics and Davide, what’s the second paper focused on?
Interviewee: Davide Castelvecchi
This team has looked at this catalogue of possible crystals and has said based on the symmetry; we know that there is potentially a topological state of matter in any material that has a structure.
Interviewer: Adam Levy
So it’s kind of telling people where to look for these topological phenomena?
Interviewee: Davide Castelvecchi
Yes exactly and experimentalists seem to be quite excited because it could be a shortcut to discovering many more, potentially thousands, of new topological materials.
Interviewer: Adam Levy
Even more complex than pretzels?
Interviewee: Davide Castelvecchi
Potentially, yes.
Interviewer: Adam Levy
Thank you Davide Castelvecchi and Lizzie Gibney for helping me find my way around this bemusing but interesting subject a little better. If this has given you a taste for topology, do make sure to check out Davide’s feature at nature.com/news as well as the two new topology papers there at nature.com/nature.
Interviewer: Shamini Bundell
Still to come, we’re taking a look at the state of the climate in the News Chat, featuring accelerating sea level rise, and, how France is wooing US climate scientists. Now though, it’s time for the Research Highlights.
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Interviewer: Shamini Bundell
Sea spiders have been harbouring a secret, well, besides not being actual spiders. These crustacean pretenders use their guts to pump their blood-like fluid. The crabby critters do still have hearts but it seems these aren’t pumping down their long limbs. Fortunately, the spiders’ sprawling guts have taken on that extra leg work. Researchers studied respiration in a range of sea spider species. They found that the guts which branch out into the spiders’ legs were pulsating. These gut contractions get the oxygen all around the beast’s entire body. And if that isn’t weird enough, sea spiders breathe in through their legs. Dive into that respiration revelation now at Current Biology.
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Interviewer: Shamini Bundell
In the on-going arms race between bacteria and viruses, some bacteria invented a system called CRISPR Cas-9 to chop up viral DNA. In response, some viruses invented CRISPR inhibiting proteins to defend themselves. These days scientists use CRISPR to snip particular bits of DNA and it’s become a game changing gene-editing technique. But now researchers are turning to CRISPR inhibiting proteins to help improve their gene-editing accuracy. An anti-CRISPR protein which usually prevents CRISPR Cas-9 from targeting DNA is added to the system after the gene-editing had begun. This reduces the number of CRISPR cuts in the wrong parts of the DNA. Read more on this cutting edge find in Science Advances.
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Interviewer: Adam Levy
At the 2016 Rio Olympics, Usain Bolt continued his winning spree and won 3 gold medals. Seeing him towered over his competitors, you could be forgiven for wondering whether his size was key to his victory, if you managed to get a good look at him before he whizzed off into the distance, that is.
Interviewer: Shamini Bundell
But bigger doesn’t always mean faster, especially across the whole animal kingdom. If it did, cheetahs racing across the Savannah would find themselves being overtaken by high speed elephants, and blue whales would be zooming through the ocean out-swimming pretty much everything. Biologists have puzzled over what determines animals’maximum speeds for decades, but none have yet come up with an explanation that works on land, in water and in flight. Now, Myriam Hirt and her team seem to have had a Eureka moment and created a model that works for everything. Well, almost. Reporter Geoff Marsh was brought up to speed.
Interviewer: Geoff Marsh
This question about what limits an animal’s top speed, it’s funny because it sort of seems like a really simple question doesn’t it?
Interviewee: Myriam Hirt
Yeah it’s a really simple question and surprisingly the answer is also really simple.
Interviewer: Geoff Marsh
So generally then, when we look at animals, as they get bigger, they tend to get faster? That’s a general principle?
Interviewee: Myriam Hirt
Yeah, that was the general principle because in ecology I think we first of all always think of things increasing or decreasing continuously with body mass and with maximum speed, people already came across this phenomenon that the largest species tend to get slower again.
Interviewer: Geoff Marsh
It’s sort of intuitive why the smallest animals are slower, you know, because they’ve got shorter legs, fins, wings or flippers, but what have been the previous theories for why the biggest animals are not the fastest?
Interviewee: Myriam Hirt
Most of the time it was morphologically or biomechanically explained.
Interviewer: Geoff Marsh
So if an elephant were to run as fast as a cheetah proportionally to its body size, it would just break its own legs with the force of hitting the ground?
Interviewee: Myriam Hirt
Yeah.
Interviewer: Geoff Marsh
What’s wrong with that theory?
Interviewee: Myriam Hirt
I think it just doesn’t explain the pattern very well. So, you can’t predict maximum speeds correctly with that, which our model can.
Interviewer: Geoff Marsh
Let’s just try and visualise this for our listeners. If you’ve got body size plotted against maximum speed, what does the curve look like?
Interviewee: Myriam Hirt
So the maximum speed increases from the smallest animals to the intermediately sized ones. So, this is the size class of the cheetah and then the speed starts to decrease again.
Interviewer: Geoff Marsh
Right so it’s sort of like an upside down ‘U’?
Interviewee: Myriam Hirt
Yeah.
Interviewer: Geoff Marsh
You and your team then have tried to create a mathematical model which can explain the shape of that curve basically and then go on to predict animals’ top speeds.
Interviewee: Myriam Hirt
The important point is that larger animals need more time to accelerate their larger bodies to high speeds. And at the moment to get up to full speed, they already run out of energy, so if they had infinite time available to accelerate, then they could reach their theoretical maximum possible speed, which would be faster than the intermediately sized animals.
Interviewer: Geoff Marsh
It’s so striking that you’ve come up with this very sort of basic idea and we’ve been thinking about this question for, is it, centuries?
Interviewee: Myriam Hirt
Yeah, it is.
Interviewer: Geoff Marsh
Were you in the bath? Was this a Eureka moment? What happened?
Interviewee: Myriam Hirt
No, it was not in the bath. It was just when we were standing in front of the whiteboard: a very important moment but not very spectacular.
Interviewer: Geoff Marsh
The other nice thing about this model is that it works for animals flying in the air and swimming in water as well. Is this the first model that manages to encapsulate all of these different modalities of movement?
Interviewee: Myriam Hirt
Yes it is. So, we compiled a really large database which contains more than 450 species. We then fitted our model predictions to that so it fitted perfectly which surprised us. And I also included swimming and flying animals. And then I realised that this pattern also holds for the other movement types which makes it even more interesting.
Interviewer: Geoff Marsh
But there are outliers aren’t there because one jumped out at me and that was us. We as humans sit in the real peak of this body mass range where we should actually be almost at cheetah level but good luck to anyone who tries to outrun a big cat.
Interviewee: Myriam Hirt
But I think it kind of makes sense because we’re just not adept at high speed movement because there’s no need to be.
Interviewer: Geoff Marsh
So I guess this model then is interesting because it raises interesting questions when a species deviates from that pattern.
Interviewee: Myriam Hirt
Yeah exactly, so, with the positive deviations we can see, for example, how co-evolution between predator and prey, or negative deviations. It just shows that there is no need to develop high speed movement.
Interviewer: Geoff Marsh
Now that you’ve got this model, I suppose that it’s also going to be useful for palaeontologists, for example. They can go back and ask questions about the movement capabilities of long extinct species?
Interviewee: Myriam Hirt
Yeah, that’s one cool part about our model, that it also makes adequate predictions of maximum speeds of dinosaurs for example.
Interviewer: Geoff Marsh
Yeah, because there’s always been a big debate raging about T-Rex, hasn’t there? How fast was Tyrannosaurus Rex?
Interviewee: Myriam Hirt
So our model will predict the maximum speed of 27 kilometres per hour, so it’s not that fast.
Interviewer: Geoff Marsh
Right, okay, so they’d have to update that scene in the first Jurassic Park.
Interviewee: Myriam Hirt
Definitely, but I think the smaller ones, Velociraptors, they were really fast so you should probably not try to run away from them. That won’t work.
Interviewer: Shamini Bundell
Interviewer: Adam Levy
Interviewee: Jeff Tollefson
Hello Adam.
Interviewer: Adam Levy
Now, firstly, sea levels are going up. There’s no big news there. But we now understand the rates of sea level rise much clearer than we did before. What was actually holding us back from seeing this picture?
Interviewee: Jeff Tollefson
So we’ve only learnt about this problem recently. We’ve had this record for 25 years and scientists have been looking at it and for a long time they really couldn’t see any acceleration in the rate of sea level rise which raises some questions because we’ve got more heat going into the ocean. We’ve got more greenhouse gas emissions going into the atmosphere. The original satellite that went up to begin taking measurements of sea levels in 1992, it had two sensors on it and we switched over from one sensor to the other in 1999. What scientists have now determined is that there was a calibration on that first sensor that was applied and once they removed that calibration then you could begin to see this acceleration in the rate of sea level rise between 1992 and today.
Interviewer: Adam Levy
So does this correction bring things much closer in line with what we’d expect from other sources of data?
Interviewee: Jeff Tollefson
That’s exactly right. I mean, there were a few papers out there several years ago that said if you look at the rate of sea level rise in the 1990s, the early years, and then you look at the rate later they show perhaps even a decline in the rate of sea level rise which is a bit of a mystery. Two teams tackled this with different approaches over the last 2 or 3 years and those teams raised questions. They said looking at the tide gauges, we would expect to see an acceleration of sea level rise and another team took a budget approach. They looked at all the sources of sea level rise from expanding water due to heat uptake, to melt from Greenland and Antarctica and when they added these things up they saw an acceleration that wasn’t visible in the satellite record. So that led a team of scientists to start looking at what was wrong with the record and once they discovered this calibration then, all of a sudden the acceleration rate became more apparent.
Interviewer: Adam Levy
It must seem like an I-told-you-so moment for those groups who were saying there must be something wrong with this satellite data.
Interviewee: Jeff Tollefson
I suppose so but I think the bigger issue here is now we’ve got multiple groups coming at it from multiple angles and they’re all coming to the same conclusions so it sounds like we’ve resolved this minor mystery in the climate world.
Interviewer: Adam Levy
And in terms of what we now understand is happening with sea levels, how rapid is this acceleration?
Interviewee: Jeff Tollefson
So there are still some uncertainties. We can’t say precisely but if we look at the central values what we see is a rise from 1.9 millimetres in 1993 to 3.9 millimetres in 2016. And that calculation also requires removing other confounding factors and that’s where some of the uncertainty comes in.
Interviewer: Adam Levy
And is the expectation that this acceleration will continue into the future?
Interviewee: Jeff Tollefson
Well, we don’t know. The way it was described to me is that it’s probably safe to think about this as kind of a flaw. If you project forward over one hundred years you get 75 centimetres of sea level rise and maybe we can think about that as a likely minimum. Nobody sees why you’d see a deceleration of sea level rise unless we, we being humanity, substantially reduce greenhouse gas emissions but if things continue as normal you would expect that to continue. So the question looking out many decades is whether you’ll see a sudden acceleration of melting in say, Greenland or West Antarctica or even East Antarctica. If you get a big change in the rate of ice melt those areas then it could be even larger.
Interviewer: Adam Levy
A lot of future climate research is now in doubt because of changes to the US administration but President Macron of France is trying quite hard to woo climate scientists over across the Atlantic and it seems like it’s working.
Interviewee: Jeff Tollefson
Yeah, so, President Macron has created a 60 million Euro plan to basically fund some scientists and lure scientists from other countries to France and apparently the way this works is you can get grants up to four years’ worth, up to 1.5 million Euros. That’s a substantial sum of money and apparently they are attracting quite a bit of interest from the US and presumably other countries. I guess the question here is whether this is an anti-Trump vote by US scientists who opt to apply for this programme or whether it’s a pro-opportunity type of choice. There’s always limited funding in science. If you throw up a new programme that has a bunch of money, scientists are going to pursue that and this is a very International sphere and probably you’ve got a lot of scientists that’d be more than happy to go and pursue a big opportunity in France.
Interviewer: Adam Levy
How many scientists can they actually hire through this scheme and how many people are applying?
Interviewee: Jeff Tollefson
Well it sounds like they’ve got 4500 applications in so far. Apparently the goal is to whittle that down to around 50 winners and I guess that decision will be made later this year in November.
Interviewer: Adam Levy
Is France really as research friendly as this makes it seem? This makes it sort of seem like a Utopia for troubled American researchers.
Interviewee: Jeff Tollefson
Yeah, well, that’s the irony and some French scientists have honed in on exactly that point. At the same time that they’re proposing this big programme to lure people from outside, the French government is also proposing to scale back funding for research and higher education at home. So, one way to look at this is that it’s really kind of about optics and perhaps it’s just a poke in the eye of the Trump administration because if France isn’t funding science at home then it’s hard to make the case that they’re really serious about advancing research and development.
Interviewer: Adam Levy
And it’s not a huge number of climate scientists that they will be able to hire. Is there any hope for American climate scientists who don’t make it onto this French programme?
Interviewee: Jeff Tollefson
Well, I think American climate scientists just have a big question mark hanging over their heads right now. Probably the majority are going to try and stick it out here and the question that we can’t answer at this point is what the budgets are going to look like going forward for climate research, for energy ‘R’ and ‘D’. But it’s entirely possible and perhaps even likely that budgets are going to go down and that does signal bad news for the research community.
Interviewer: Adam Levy
Thank you. Jeff. To keep up with all things climate and of course all other science news, make sure to head to nature.com/news.
Interviewer: Shamini Bundell
That’s all for this week but make sure to follow us on Twitter @NaturePodcast. Or if you want more personal tweets, I’m @sbundell.
Interviewer: Adam Levy
And my witterings can be found @ClimateAdam. Thanks for listening. I’m Adam Levy.
Interviewer: Shamini Bundell
And I’m Shamini Bundell.
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