Podcast: The quantum space lab

Host: Shamini Bundell

Welcome back to the Nature Podcast. This week, quantum experiments in space…

Host: Nick Howe

And what determines the height of a mountain. I’m Nick Howe.

Host: Shamini Bundell

And I’m Shamini Bundell.

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Host: Shamini Bundell

Before we start today’s show, you might have noticed that it’s a day later than normal. That’s because we – and Nature as a whole – spent yesterday taking part in the #ShutDownSTEM movement. So, instead of business as usual, we tried to dedicate the time to educating ourselves and defining actions that we can take to eradicate anti-black racism in academia and in STEM.

Host: Nick Howe

We’ll put some links in the show notes with more information about that, and we’ll chat more about that in next week’s show. Returning to this week, though, Shamini, what have we got first in the show?

Host: Shamini Bundell

Well, first up, you might have had to make some changes in your day-to-day life because of having to work remotely. Well, a number of scientists at the Jet Propulsion Laboratory at NASA have taken remote work to the extreme, controlling a physics experiment on the International Space Station from the ground. Here’s remote podcaster, Geoff Marsh, with the story.

Interviewer: Geoff Marsh

Have you pressed record on the voice memos?

Interviewee: Rob Thompson

Okay, now, yeah.

Interviewer: Geoff Marsh

By the looks of this video call, you’re not at NASA. You’re in your basement.

Interviewee: Rob Thompson

Yeah, we’ve been operating the Cold Atom Lab remotely from our homes since the middle of March. So, it’s a little bit strange with everything going on in the world to sit down in front of a computer and be talking to an instrument that’s on the International Space Station, kind of zipping around over our heads at 17,000 miles an hour and so on. It took a little getting used to. My name’s Rob Thompson. I’m a scientist working on a project called the Cold Atom Lab that’s on board the International Space Station. It is a multi-user facility to study ultra-cold matter at temperatures very close to absolute zero. It traps atoms with magnetic fields on something called an atom chip and uses techniques of evaporative cooling to cool those atoms down to very cold temperatures so that they form a Bose condensate.

Interviewer: Geoff Marsh

Why are physicists so keen to create these little clouds of this kind of unique quantum state of matter?

Interviewee: Rob Thompson

One of the things that sort of fascinates me about them is that we can think of it as kind of a magnifying glass for the quantum world.

Interviewer: Geoff Marsh

No one is helping with the instrumentation up there on the Space Station, are they?

Interviewee: Rob Thompson

Yeah, we operate it completely remotely from the ground, so there’s no day-to-day operations. The astronauts don’t help us. One of the things that we’re fairly proud about this mission is that it really does demonstrate that you can do, I think, some very sophisticated science that previously could only be done in a laboratory setting on Earth. We do rely on the astronauts for the initial installation, but the system is also designed to be repairable and upgradable, and so we just recently have had an upgrade where the astronauts kind of replaced the heart of the instrument, which is the science module that contains the vacuum system and atom chip and those kinds of things.

Interviewer: Geoff Marsh

As you’ve said, nowadays, these Bose-Einstein condensates are created quite routinely in hundreds of labs around the world. Why go to all the effort to perform these experiments in microgravity on the Space Station?

Interviewee: Rob Thompson

So, one thing is we just get to look at the atoms for a longer amount of time if they’re just kind of floating, and that means that, for certain very sensitive measurements, you get a much more powerful enhancement. In fact, if you’re trying to measure accelerations or, alternatively, gravity using an atom interferometer, you get a really big improvement in the sensitivity. So, we ultimately think that a lot of these types of quantum sensors, they belong in space. There’s lots of things out in space that we might want to measure, things like tests of general relativity. People have proposed searches for candidates for dark energy and dark matter. People have proposed using these as a tool to search for gravitational waves as well. Beyond that, there’s actually just a lot more basic science that can be done with ultra-cold atoms. One of our principal investigators is doing an experiment where he is trying to make what we call quantum bubbles – spherical-shaped condensates – and they’re just impossible to make on the ground where gravity would pull the atoms down to the bottom of whatever trap that you put them in. In the absence of gravity, they can spread around and form this sort of bubble. One of the things that we will be trying to do in the near future is look at mixtures of different types of cold atoms – rubidium and potassium – at the same time. If you try to do those types of experiments on Earth, you do have to worry about the fact that the rubidium is heavier so it tends to pull down to the bottom of the trap compared to potassium, so you don’t get these perfectly overlapping mixtures and clouds.

Interviewer: Geoff Marsh

And the Cold Atom Lab also allows you to achieve colder atoms.

Interviewee: Rob Thompson

Yeah, one of the sort of standard ways that we get these gases colder once we’ve produced a Bose condensate is simply to relax the trap and make it weaker and weaker. As it gets weaker, the atomic cloud expands and as we do that, the atoms get cooler and cooler and cooler. You can do that on Earth, but eventually, the tug of gravity will make the atoms kind of spill out of your trap, so there’s kind of a limit to how weak you can make a trap on Earth. In space, you don’t have that limitation. There’s no fundamental limit to how cold we could get them.

Interviewer: Geoff Marsh

Presumably, just the restrictions of having to be an instrument that was transported up to space and operate unmanned in space poses lots of its own limitations?

Interviewee: Rob Thompson

Yeah, that’s absolutely true, and just in terms of how big a condensate you can make, it’s nice that for the magnetic field, things sort of scale pretty nicely. The trap strengths actually get a little bit stronger. But that’s not true for the laser cooling and for laser cooling you want the biggest beams you can have to collect the most atoms in the fastest way, and so there is a trade-off there between size and weight and how many atoms you can collect.

Interviewer: Geoff Marsh

Is it a bit like a synchrotron or a big telescope where like lots of different research groups can book in some time?

Interviewee: Rob Thompson

Yeah, and this is actually very interesting because this is, of course, the particle physicists and the astronomers have been working on this paradigm for decades, right? But it’s not the way atomic physicists work, that we’re used to building our own instruments and turn knobs as we see fit.

Interviewer: Geoff Marsh

I wonder what that will do to the science output? In some ways, you might think that having a diversity of minds using such a sophisticated instrument could bear more fruit.

Interviewee: Rob Thompson

Well, yes, I think so because we do weekly meetings with the PIs and they talk about their results and they share back and forth. It’s going to be an interesting new paradigm.

Host: Shamini Bundell

That was Rob Thompson from the Jet Propulsion Laboratory at NASA in the US. You can find the full paper in the show notes.

Host: Nick Howe

Coming up, we’ll be hearing about the debate surrounding the height of mountains. Before that, though, it’s time for the Research Highlights, read by Dan Fox.

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Dan Fox

Researchers have developed a new way to trace goods from suppliers all the way to your home – barcode microbes. The team have inserted short DNA sequences into the genomes of a harmless bacteria and a yeast. These sequences then serve as biological barcodes that can be used in different combinations and identified with several DNA-detecting tools. The barcoded microbes were sprayed onto sand, soil, carpet and wood, and remained detectible for months, even after exposure to wind, rain and vacuuming. Using the DNA-tagged bacteria, the researchers were able to trace a leafy plant all the way back to the specific pot in which it was grown. The microbes are resilient enough to persist on produce, even after washing and cooking. So, the approach could provide a new way to track food back to its source should any problems arise. Trace that full research back to its origin in the pages of Science.

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Dan Fox

Physicists have made the most realistic calculations yet of what a cyclist would look like as they moved towards you, if they were travelling close to the speed of light. Einstein’s special theory of relativity implies that the dimensions of a fast-moving object are squashed along the direction of motion. For an observer, this would mean the cyclist would be grotesquely distorted, with their back visible even when they were approaching, something the team have visualised. And the researchers speculate that because our two eyes would receive different distortions as the light-speed cyclist passed, a human observer might even suffer from motions sickness just by looking at them. It’s hoped that this work could help astronomers to design sensors for future high-speed interstellar probes. Observe that research, close to the speed of sitting down, at Proceedings of the Royal Society A.

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Interviewer: Nick Howe

Next up, what controls mountain height? The tectonic plates of our planet drift slowly over the liquid rock beneath. When two plates collide, the land buckles like a crinkled sheet of paper and mountains are pushed upwards, sometimes to incredible heights. But once these mountains are formed, what keeps them so high? It’s likely a combination of factors, such as erosion and ongoing tectonic movement, but a key question in geoscience is to identify the main driving force behind mountain height.

Interviewee: Armin Dielforder

So, the one idea would be it is erosion, that it is outpacing the tectonic control, or is the dominant effect tectonic control outpacing the erosional effect?

Interviewer: Nick Howe

This is Armin Dielforder. It’s a widely held view among scientists that erosion is the main controller of mountain height. But this week in Nature, Armin and his colleagues suggest the opposite – that tectonic forces are in the driving seat. To start, Armin calculated the tectonic forces that act on mountains as two plates are colliding at so-called convergent plate margins. From this, he could get an estimate of how high mountains could theoretically be. Now, if erosion was the main factor determining mountains’ heights, then you’d expect these estimates to be much higher than the actual height – the mountain would have been eroded away – but this wasn’t the case in Armin’s analysis.

Interviewee: Armin Dielforder

It matched quite well, and that was also a big surprise for us to see that all around the globe we find that the match between the true height and the theoretical height, which could be supported by the forces, matched so well.

Interviewer: Nick Howe

This doesn’t mean that erosion has no effect on mountain height. It’s just that Armin’s analysis suggests that the effect of erosion is dwarfed by that of tectonic influences. And this held true across the world in different climatic zones which have different rates of erosion. Now, like I said before, it has been a widely held view that erosion has been the main factor in controlling mountain height, and many papers have shown this, so I asked Armin how he reconciles this past data with his new finding.

Interviewee: Armin Dielforder

That is a very central question. So, one key aspect that I see is that in previous studies that either address the erosional control or also the tectonic control, we had always the problem that the magnitude of absolute forces were not clear and by that, it was always very difficult to say what is the height a mountain range could theoretically have if it were controlled by tectonics, but we were lacking this kind of information. What we followed in our study is to provide exactly this kind of information.

Interviewer: Nick Howe

As understanding of tectonic forces has grown significantly over the past few years, Armin says they are now able to calculate the forces that are relevant to mountain height with much more accuracy. Their conclusion that tectonics is the dominant factor may not hold for every mountain though. Armin’s analysis was dominated by mountains formed at subduction zones – places where one tectonic plate dives under the other as they move together. So, do tectonic forces still dominate when mountains are formed in other ways?

Interviewee: Armin Dielforder

This is an aspect that needs to be further investigated. From the findings that we have so far, which also includes the Himalayas, our understanding is that this finding is applicable to most mountain ranges at convergent plate margins. Mountain ranges can also form within the interior of continents. The tectonic framework differs a little bit from what we are looking at and at present, we couldn’t perform our analysis for this setting, and this would be something that would be very interesting to address in future, to see if we find a similar control or if maybe there, erosion can have a stronger effect compared to subduction and standard collision zones.

Interviewer: Nick Howe

There’s likely still a lot more work to be done in order to solve the mountain height debate. Erosion could be more of a factor for certain types of mountains, and the forces at play may change throughout time as well. For Armin, that is the key question.

Interviewee: Armin Dielforder

And this is actually an aspect that is, at present, very poorly understood in geoscience – how does the topography of mountain ranges change through time? And these findings that we have now may provide another important aspect to better address, in the future, the temporal evolution and the dynamic evolution of mountain ranges, and there I see a lot of open questions.

Interviewer: Nick Howe

That was Armin Dielforder from the Helmholtz Centre Potsdam in Germany. You can learn more about mountains by checking out the paper and an accompanying News and Views article in the show notes.

Host: Shamini Bundell

Last up, it’s time for a look at some other non-corona science news highlighted in the Nature Briefing – that’s Nature’s daily pick of science news and stories. So, Nick, what have you chosen this week?

Host: Nick Howe

Well, I’ve been looking into why sleep deprivation kills.

Host: Shamini Bundell

That is something that I very much welcome. I am a big fan of sleep, so any excuse to have more of it.

Host: Nick Howe

Well, this is definitely a good excuse. So, for a long time, scientists have understood that if you have no sleep at all, 100% sleep deprivation, then various studies have shown that animals die, but the question has always been why? It’s not really been clear. But now, new research has suggested that it might be something that’s going on in the gut.

Host: Shamini Bundell

So, you mean how if you eat lots of cheese, you’re supposed to have weird dreams?

Host: Nick Howe

Laughs. Well, it’s not really concerning that. This is about what happens in your intestines if you have a lot of sleep deprivation. So, there’s been some studies that have been depriving flies of sleep by shaking them about so they can never sleep or genetically engineering them so they won’t sleep either, and what seems to happen with these flies is there’s a build-up of molecules in the gut that destroy DNA – these so-called reactive oxygen species – and it seems like from their studies, that’s what’s actually causing the destruction of organs and death from sleep deprivation.

Host: Shamini Bundell

So, when the flies couldn’t sleep, which is really mean by the way, but when they were sleep deprived, these molecules were building up and when you let them sleep, the molecules go away again.

Host: Nick Howe

Yeah, and what was really fascinating about these studies is it was a build-up of reactive oxygen species and so the researchers said, ‘What if we give the flies antioxidants?’ And so, they did, and the flies lived as long as flies that slept normally, and the researchers said they even looked good as well. So, it seems like that is a key factor for it. Although, I must say, this is flies. It’s not humans. We’re a little bit more complicated than that. But still, super interesting finding.

Host: Shamini Bundell

Can I just query just your casual throwing in there of – ‘the researchers even said the flies looked good.’ That seems inappropriate.

Host: Nick Howe

It was a direct quote from one of the researchers. Laughs.

Host: Shamini Bundell

What does that mean? Like they looked healthy, I guess?

Host: Nick Howe

I guess they mean they looked healthy. The article didn’t expand on that quote. I think they just put it in there because it’s a brilliant quote, but they didn’t actually expand on what that meant. The flies looked good. They were good-looking flies. So, Shamini, what have you found this week?

Host: Shamini Bundell

So, my pick from this week is a discovery from Mexico of this huge structure built 3,000 years ago by the early Maya civilisation that is kind of huge and out in the open, but no one had ever realised it was there before.

Host: Nick Howe

So, I guess my first question is how did they not notice it was there if it’s huge?

Host: Shamini Bundell

Laughs. Well, so we’re not talking giant stone pyramid that was just loitering around. It’s under the earth, but it’s 13-feet-high and half-a-kilometre-long. It’s this huge basically square platform, and the reason it’s sort of hard to spot is that if you look at a photo of sort of where it is, it’s covered by patches of forest, there’s ranch land sort of breaking up the sort of like clear shape, and in a way, it’s sort of so huge that it was sort of impossible to see from close up. But they were doing a sweep with LiDAR from a plane that’s intended to look sort of through trees and things to actually sort of see the shape of the ground underneath, and when you look at the LiDAR image, suddenly there’s this really clear sort of rectangular, tall platform, and it’s even got a little pyramid on it as well. I say little – a 13-foot-tall pyramid on it as well and various other buildings associated with it.

Host: Nick Howe

Wow, and so, what is the sort of significance of this? The Maya were building stuff all the time, weren’t they? Is it too surprising that they built this structure?

Host: Shamini Bundell

So, there are a couple of unique things about this. One is that it’s huge and it’s sort of the biggest thing like this that we know from the Maya, and the other is that it’s actually really old and it’s the oldest of these sort of big structures that they built. And the archaeologists think that this was from when they were just moving into a sort of more sedentary lifestyle, and maybe this was actually built why they weren’t living permanently in one place and they were still moving around, which is also amazing because it’s so big, there’s so much earth that would have had to have been moved to create this tall platform that would have taken thousands of people several years to actually build it.

Host: Nick Howe

And do we know why they built it?

Host: Shamini Bundell

Well, the archaeologists say that this would have been a sort of cultural centre, a place for ceremonies, gatherings, maybe processions, rituals. But to be honest, we don’t know. We only have the sort of bare bones of what they left behind, which is kind of part of the excitement and the mystery of it. But that was what I found interesting this week. So, there’s a link to that one in the show notes, and if anyone wants more science stories but instead delivered as a daily email, you can check out the Nature Briefing, and there’s a link to that in the show notes as well.

Host: Nick Howe

That’s all for this week. If you want to get in touch with us then you can reach us on Twitter – we’re @NaturePodcast – or send us an email – we’re podcast@nature.com. I’m Nick Howe.

Host: Shamini Bundell

And I’m Shamini Bundell. Thanks for listening.