• NATURE PODCAST

The smallest measurement of gravity ever recorded

Hear the latest from the world of science, with Nick Petrić Howe and Shamini Bundell.

In this episode:

00:47 Gravity, on the small scale

This week, researchers have captured the smallest measurement of gravity on record, by measuring the pull between two tiny gold spheres. This experiment opens the door for future experiments to investigate the fundamental forces of nature and the quantum nature of gravity.

Research Article: Westphal et al.

News and Views: Ultra-weak gravitational field detected

07:37 Research Highlights

Research shows that people often don’t know when a conversation should end, and the cuttlefish that show remarkable self control.

Research Highlight: How long should a conversation last? The people involved haven’t a clue

Research Highlight: Arms control: cuttlefish can pass the ‘marshmallow test’

10:18 Lamprey evolution

The larval stage of lamprey growth has long been thought to resemble the kind of early animal that all vertebrates evolved from. However, new research looking at the fossils of lamprey species suggests that this popular hypothesis may be incorrect.

Research Article: Miyashita et al.

17:38 Briefing Chat

We discuss some highlights from the Nature Briefing. This time, glow-in-the-dark sharks, and scientists’ reflections on the nuclear industry 10 years on from Fukushima.

The Guardian: 'Giant luminous shark': researchers discover three deep-sea sharks glow in the dark

Nature Comment: Nuclear energy, ten years after Fukushima

Subscribe to Nature Briefing, an unmissable daily round-up of science news, opinion and analysis free in your inbox every weekday.

Video: Deep-sea soft robots

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Transcript

Hear the latest from the world of science, with Nick Petrić Howe and Shamini Bundell.

Host: Nick Petrić Howe

Welcome back to the Nature Podcast. This week, observing gravity on a tiny scale…

Host: Shamini Bundell

And what lampreys can tell us about vertebrate evolution. I’m Shamini Bundell.

Host: Nick Petrić Howe

And I’m Nick Petrić Howe.

[Jingle]

Host: Nick Petrić Howe

First up on this week’s show, reporter Adam Levy has been looking into how an experiment on a very small scale could tell us a lot about the forces that govern the Universe.

Interviewer: Adam Levy

Gravity – to a non-physicist this force might seem pretty run of the mill, done and dusted. After all, we all know the story about Newton and the apple. But for physicists, this simple picture hides a wealth of mysteries about our Universe. There are four forces that govern the Universe – gravity, electromagnetism and the strong and weak nuclear forces. But gravity seems different from the other three. For one, it’s not clear whether it operates in a quantum way, which we know the others do. For another, there are the big unknowns of dark matter and dark energy which could point towards gaps in our understanding of gravity. So, physicists need a way of testing gravity.

Interviewee: Markus Aspelmeyer

And it turns out that gravity experiments on the very small scale can provide answers to all of these domains.

Interviewer: Adam Levy

This is Markus Aspelmeyer, a physicist who has done exactly that in a paper out in this week’s Nature – measure gravity on the very small scale. So, Markus and I had a weighty chat all about the experiment. We started by discussing the reason these experiments are so challenging – the fact that gravity is incredibly weak compared to the other forces.

Interviewee: Markus Aspelmeyer

If you have two very tiny particles, let’s say atoms, each of them just carries one charge. The electromagnetic force between them is 40 orders of magnitude larger than gravity between those two objects. That’s a 1 with 40 0s at the end. You can see how small this actually is. The reason why we experience gravity in our everyday life is that the Earth is so huge it contains so many atoms, and this is where the large gravitational force then builds up.

Interviewer: Adam Levy

So, you actually wanted to investigate gravity on very small scales between very small masses. What is your approach to investigate this?

Interviewee: Markus Aspelmeyer

So, our experiment builds on an idea that is quite old. It goes back more than 200 years. What we start off with is a small pendulum that is very sensitive to external forces. What we do now is we have a small gold mass, only a millimetre in size, that creates a gravitational field. And we shake the gold mass now back and forth and as a consequence our little pendulum also starts to shake, and we are measuring the tiny displacement now of the pendulum. And this is on the order of a millionth of a millimetre, and from this tiny movement we then learn about the force that acts on this pendulum.

Interviewer: Adam Levy

Now, just how much smaller are the masses that you’re looking at here compared to what has been done in previous experiments?

Interviewee: Markus Aspelmeyer

So, in most experiments to date, people are focusing on measuring gravity more and more precisely, and they typically do that with masses on the order of a kilogram. So, that’s like 10,000 times more massive than what we are using in our experiment. There are also experiments that measure gravity at very short distances and they use masses that are approximately ten times bigger than ours. What we have is now in our tiny gold sphere, which basically is the size of a beetle approximately, if we would be stand on the surface of that little planet and let something fall, it would actually fall something like 10 billion times slower than on the surface of the Earth.

Interviewer: Adam Levy

Now, the forces that this tiny mass generates are really, really tiny, so how do you go about this so you don’t just get signals from background noise, from other interference?

Interviewee: Markus Aspelmeyer

That was in fact the biggest challenge for this experiment. So, our experiment was so sensitive to external noises that we would see pedestrians walking outside on the street and we saw earthquakes all over Europe showing up in our data and so on and so on. The real challenge was to very carefully monitor the noise and also to restrict measurements to times where there was less noise. So, for example, the best data we could take was during the Christmas season which was extremely quiet where not so many people were on the street and so on.

Interviewer: Adam Levy

Okay, so this is how you actually set up the experiment and try and get the best possible result, but what were your results? What do they show about gravity?

Interviewee: Markus Aspelmeyer

The fact that we can measure the gravitational field generated by a tiny millimetre-sized gold mass is completely fascinating to me, and of course the very first question was, ‘How do we know it’s gravity?’ So, corroborating our results to being sure that we have seen gravity, this was another half a year of work.

Interviewer: Adam Levy

And do we see anything, I suppose, unexpected about how gravity is behaving at these tiny scales?

Interviewee: Markus Aspelmeyer

So, at this point in time, we have not seen anything unexpected and we also did not expect anything unexpected, I have to say. Even more interesting is now the path forward. So, we want to go to even much smaller masses. We think we already know how we can make our apparatus sensitive to the level of going down another factor of 1,000. If we are small enough then the hope is that we can manipulate these very small objects even in a way that they obey the laws of quantum physics. And if they do, then we can ask the question, ‘How does a quantum object gravitate?’ This is completely unexplored territory. Probing gravity in these small, small machines and in the very long run potentially combining it with questions and phenomena of quantum physics is very intriguing.

Host: Nick Petrić Howe

That was Markus Aspelmeyer from the University of Vienna in Austria. For more about tiny gravitational experiments, check out the show notes for a link to his paper and an accompanying News and Views article.

Host: Shamini Bundell

Talking about tiny things, later on we’ll hear about some relatively small ancient lampreys. Right now, though, it’s time for the Research Highlights with Dan Fox.

[Jingle]

Dan Fox

Would you say that I’ve been talking for too long? Because new data suggests that when two people talk, one party almost always wants the conversation to end before the other. Researchers asked over 800 people to complete an online survey about a recent conversation. The team also paired up 252 strangers in laboratory studies and asked them to chat for between 1 and 45 minutes. In both groups, around two thirds of participants felt ready for the conversation to end before it did, but one third wanted the chat to continue. In the lab studies, none had any idea when their partner wanted to stop talking and all underestimated how different their partners desires were from theirs. The researchers conclude that ending a conversation is a coordination problem caused by the fact that individuals keep information from each other and as a result, most conversations appear to end when no one wants them to. If you’re not ready for that research to end, you can read the paper in full at Proceedings of the National Academy of Sciences of the Unites States of America.

[Jingle]

Dan Fox

Researchers have found that cuttlefish can defer gratification and the ten-limbed molluscs that can hold out the longest also score best on learning performance. The ‘marshmallow test’ is a famous experiment in delayed gratification. A child receives a marshmallow and is given a choice – eat it straight away or wait 15 minutes and receive a second treat. Researchers devised a version of this test for common cuttlefish. They analysed how often the animals will wait to receive their favourite snack – a live grass shrimp – rather than eat a less preferred but already available prey. Some cuttlefish waited over two minutes for the shrimp and cuttlefish able to hold out for longer also performed better on tests that measured learning skills. The team think that this is the first evidence of a link between self-control and learning performance in a non-primate animal. Test your self-control by waiting until the end of the podcast to read that research in full at the Proceedings of the Royal Society B.

[Jingle]

Interviewer: Shamini Bundell

Next up, I’ve been looking into a paper about some fossil lampreys. The paper came with a lovely reconstruction of one of these lampreys, which Nick really appreciated me showing him the picture of.

Host: Nick Petrić Howe

Erm, I’m not quite sure those are the words I would use. I think the exact term I used to describe the image was ‘nightmare fuel’.

Interviewer: Shamini Bundell

It did prominently feature a sort of jawless mouth filled with teeth.

Host: Nick Petrić Howe

Many, many teeth.

Interviewer: Shamini Bundell

But lampreys are lovely. So, I remember when I was little, my dad would take us down the stream and we’d lift up stones and find little lampreys. And they’re basically little aquatic creatures that look kind of like eels, but they’re actually from a much more primitive branch of the evolutionary tree than eels are. It’s a branch that arose before vertebrates – so that’s all animals with backbones – before they had evolved jaws. What I didn’t know back then, however, was that there was more to these slippery little lampreys than initially met the eye. So, lamprey species actually often spend most of their life looking quite different. They have a filter-feeding larval stage, and scientists have long hypothesised that this simple larval creature could represent the kind of animal that all vertebrates evolved from. But this new paper suggests that theory might be wrong. Tetsuto Miyashita is the author of a new study on the fossils of ancient lamprey species. I called him up to find out more.

Interviewee: Tetsuto Miyashita

Lampreys have a preposterous life history. So, the lampreys that you saw are the adult phase, but they start out their life with this very humble origin because those larval stage of lampreys are called ammocoetes. They’re almost like a worm-like creature. They burrow in the sand and then they sort of do a filter feed. They’re not predatory at all. They’re just basically slopping up water for whatever food particles that are passing by. So, this larval phase is one of the main reasons why people thought that lampreys are very primitive and the window to that ancestral stage.

Interviewer: Shamini Bundell

The fact that this ammocoete larvae is so primitive and simple, was the idea that both lampreys and I guess all vertebrates would have evolved from something like that and lampreys have just hung on to the primitive state?

Interviewee: Tetsuto Miyashita

Yeah, so that was the conventional wisdom. They kind of look like the amphioxus, which is another filter-feeding organism that is not a vertebrate animal. They are just a branch just outside of vertebrates. So, for about a century and a half, ammocoetes are the primary model for people to reconstruct that deep ancestry of the vertebrates.

Interviewer: Shamini Bundell

And that does make sense to some extent because, for example in the human embryo development, there are sorts of gills that start to form at one point that are maybe a remnant, so there are cases where different developmental stages can reflect the evolutionary past. But actually, you’ve now discovered new information which suggests that’s not the case here.

Interviewee: Tetsuto Miyashita

If that was the case then you would expect one thing in a fossil record. If ammocoetes are really the retention of the ancestral state then if you go back all the way into the fossil record, you would still see that larval phase sticking around, right. So, that was the assumption that we really wanted to test with this new fossil evidence.

Interviewer: Shamini Bundell

So, looking into the fossil record must have been still quite tricky because you’re looking for animals that, even in the adult lamprey’s case, don’t have hard bones, they just have this sort of cartilaginous spine. What did you find?

Interviewee: Tetsuto Miyashita

What we report in this new paper is a whole bunch of fossils that look like adult lampreys but only very small. The smallest one is about one and a half centimetres long, so that’s basically about the size of the little fingernail. Now, the interesting thing about these tiny, small lamprey fossils is that some of them actually come with the little yolk sac still attached to the abdomen, so we know that they hatch in that form. So, we can sort of put them in a series, right, so the smallest one to the largest ones, and then we scratch our head because we can’t find the filter-feeding larval phase anywhere in this series.

Interviewer: Shamini Bundell

And this is multiple species of very primitive lampreys, enough to suggest that maybe none of the primitive lampreys started out with this larval stage at all, and that was something that evolved later.

Interviewee: Tetsuto Miyashita

Yeah, no we are getting quite excited about the prospect of this because we are testing that 150-year-old assumption that the ammocoete larval phase is a holdover from this ancestral stage. So, then we thought that okay, so maybe the ammocoete larval phase is actually a recently evolved condition, so it just completely removes or decouples the ammocoete larval phase from the ancestry of the vertebrates.

Interviewer: Shamini Bundell

And you said that for a long time that ammocoete has been kind of the model and that’s what we’ve sort of looked to when thinking about vertebrate ancestors, but there are other basal not-quite-vertebrates vertebrate relatives, like amphioxous that you mentioned, which are also filter-feeders, so does this suggest that we were completely wrong about the vertebrate ancestor?

Interviewee: Tetsuto Miyashita

There is good reason to think about the filter feeding as a dominant form of feeding leading up to the vertebrate group. But it’s a completely different thing when you talk about the sort of stem of the vertebrates as opposed to the last common ancestor of all living vertebrates. As far as we can tell, there is no evidence that this last common ancestor between us and lampreys was a filter feeder.

Interviewer: Shamini Bundell

And do you have any other theories about what this mysterious last common ancestor might have been doing if it wasn’t a filter feeder? Was it predatory?

Interviewee: Tetsuto Miyashita

Ah, right, so now that we don’t have to think about the ammocoete larval phase, we turned back to the fossil record and there was actually a pretty good candidate for what the last common ancestor of us and lampreys look like. This is the fossil jawless vertebrates. They have the hard scales and they are basically deposit feeders, so they basically go into the sediment and then scoop up the mud to get the food particles in there.

Interviewer: Shamini Bundell

So, what kind of impact do you think this new discovery in this paper is going to have on the field and on our understanding of vertebrate evolution?

Interviewee: Tetsuto Miyashita

I guess what we did was making everybody’s life a little bit difficult, as far as lampreys are concerned. Oftentimes, new insights actually complicate things. This might be a bit of a tribute to Thomas Henry Huxley. Huxley is known for that famous quote. I can’t really recite it word for word, but the history of science is a series of beautiful theories destroyed by ugly facts.

Interviewer: Shamini Bundell

That was Tetsuto Miyashita of the Canadian Museum of Nature, and you can find a link to his paper in the show notes.

Host: Nick Petrić Howe

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. Shamini, what have you got for me this time?

Host: Shamini Bundell

Well, Nick, I know how much you like aquatic creatures with lots of teeth, so when I saw a story about glow in the dark sharks I was like, ‘Yes, this is the story for the Briefing chat this week, no question.’

Host: Nick Petrić Howe

Okay, well I’m a lot more appreciative of these sorts of creatures because they’re glowing in the dark. What’s going on? Why are they glowing in the dark? Do sharks glow in the dark? What?

Host: Shamini Bundell

They do! I did not know that sharks glow in the dark either and actually this is all relatively newly sort of discovered and being investigated, but quite a lot of animals do glow in the dark. So, the area that we’re talking about is basically the ‘twilight’ zone of the ocean, so far enough down that there’s not a lot of light but it’s not quite sort of pitch dark. There’s not enough light for photosynthesis certainly. And there’s a lot of animals in this kind of region that have bioluminescence, that produce their own light for various reasons. And this paper in Frontiers in Marine Science which was reported in The Guardian describes the largest yet known luminous vertebrate.

Host: Nick Petrić Howe

Okay, so when I think of things glowing in the ocean, I don’t think of sharks because they don’t want things to know they’re there, they’re like hunting stuff, so why are they glowing?

Host: Shamini Bundell

Yeah, so some of the things down there are glowing for sort of dramatic signalling purposes and you occasionally see very pretty videos of sort of beautiful displays and lights. These sharks don’t seem to be flashing and signalling at each other. And in fact, a little bit of a clue as to why they’re probably glowing is that the bioluminescent cells on their body are almost all on their underneath, on the belly. Not entirely, which is interesting, but more on the bottom than on the top. And the reason for this is that in this twilight zone it is not completely dark, which means that if you’re swimming around and something is underneath you, you’re going to be silhouetted against the light from the surface. So, the theory is or sort of main idea is that a slight glow from underneath is actually going to help you camouflage from anything seeing you from beneath.

Host: Nick Petrić Howe

Ah, so I was kind of right then, they don’t want things to see them but actually glowing a bit is a way to do that. Cool, so how do they do it because it seems like a shark is quite big, and what sort of sharks are these?

Host: Shamini Bundell

So, this is a study on three particular deep sea species of shark, one of which, the kitefin shark, is now, as I said, the biggest luminous vertebrate known, and the method of bioluminescence is still a little bit puzzling. So, they have sort of gone down and collected samples of these sharks and studied them and studied the cells that are doing the glowing, and they know a little bit about the physiology. They know that it’s not, for example, bioluminescent bacteria that’s providing that light. But there’s still quite a lot left to sort of figure out about exactly how it works and actually about exactly why because, for some of these shark species, the sort of camouflage theory works quite well because they might be avoiding predators. For one of them, maybe it’s avoiding prey seeing it, as you sort of hypothesised there, but they also found glowing cells on some of the sharks on the dorsal fin on the back, which doesn’t fit in to what we were saying about being seen from below or not, so there are lot of questions left on this.

Host: Nick Petrić Howe

As is often the way, especially with research from the deep ocean. A lot more questions than answers, but I’ll be interested to hear more about this in the future. So, the story I’ve been looking at this week is a Comment article that is reflecting on where nuclear energy is ten years after the Fukushima incident, and what questions and challenges remain for this technology to be a useful part of tackling climate change.

Host: Shamini Bundell

Right, yeah, because, I mean, the debate about nuclear energy was going on for decades before Fukushima. Did that accident – I don’t recall exactly what happened – but did that change the way people are viewing nuclear power?

Host: Nick Petrić Howe

So, the Fukushima accident was caused by an earthquake and then a tsunami that happened in Japan, and this basically caused the reactors to shut down and the whole area to be evacuated and fortunately no one died in the incident but a lot of people had to be evacuated, a lot of people were displaced, and the whole area was sort of contaminated and there was a lot of contaminated water as well. And since this incident, it’s sort of stayed in the public’s psyche. There were a lot of places that have decided that nuclear was no longer an option for them. So, for example, in Germany, really shortly after this incident, they said by 2022 they were going to decommission all their nuclear power plants and not use nuclear at all, and this is sort of almost a bit of a recurring theme for nuclear energy. There is a bit of a boom and more people are interested, there’s more investment and more plants are built, and then it goes down, and sometimes this is because of an incident – think of Chernobyl and Three Mile Island – and sometimes it’s because of economic and political reasons as well. And so, where we are ten years on, like the technology is starting to pick up again, but the authors of this Comment article, they argue that so far, when we’ve been looking at nuclear as a solution to the climate crisis, most of the time people focus on the technological aspects of it and the economic aspects, but they haven’t done enough for the moral and ethical concerns that people have.

Host: Shamini Bundell

So, in trying to shift to green energy, in trying to find sources of energy which our planet needs that isn’t contributing to climate change, nuclear seems great. But there are obvious downsides, and I can understand why people have been focused on sort of technology to decrease the chances of something going wrong, but what are these sort of bigger moral questions?

Host: Nick Petrić Howe

So, part of the problem is that there are these sort of obvious things that people focus on a lot with these sort of technological things, and that’s trying to avoid future meltdowns, trying to avoid the sort of disasters that we’ve seen, the Chernobyls, the Three Mile Islands, and stopping contamination leaking out into the environment and radiation poisoning occurring for many people. And obviously, that’s a really important thing to do, but there are also many sort of less obvious problems, and one of these is it’s sort of unequal how the risk of these things is distributed. And that’s not just necessarily like some people live close to nuclear power plants and others don’t, it’s also things like mining of the uranium that’s required for nuclear reactors. So, there’s a statistic in this article that says that almost three quarters of the uranium production comes from mines in or around indigenous communities. And so, those mines, they can cause big problems, they can poison the landscape, and the risks are borne by these people who may not necessarily have as much of a political sway, and they’re probably not going to be the beneficiaries of the nuclear power as well. And there’s also the problem of nuclear waste as well, like where do you put this, how do you dispose of it, and there are technologies that can help with this but it’s got to go somewhere and who bears responsibility for that risk? And so, there’s a lot of these sort of like more nuanced, complicated things that the authors of this article argue that the nuclear industry really hasn’t done enough to tackle.

Host: Shamini Bundell

So, obviously people have been discussing these issues, so the authors are really saying that it’s the nuclear industry’s responsibility to have these discussions, but do they propose any solutions? Is this the kind of thing that there is a solution for?

Host: Nick Petrić Howe

I mean, the solution really, it sounds kind of obvious, but it’s getting people involved. It’s getting those communities involved from the ground up in these projects. So, talking to people way before you start commissioning a plant because one of the problems that they argue is recurrent is that people will educate the people who are going to be around the nuclear facility but basically when it’s almost already done. And I think there’s one sort of line in the article that kind of summed it up for me, and it’s that, ‘They need to listen to people, not just try and convince,’ because the authors argue that most of the time it’s been a focus on education and saying how safe it is and how statistically it’s less risky than driving or something like that, when really they’re not paying attention to people’s genuine concerns, and sometimes it’s not really about like how much risk there actually is but how much people perceive that risk to be. I mean, for example, probably the most dangerous thing I do is drive around London, and it doesn’t feel very dangerous because it’s very normalised, but it’s actually statistically the thing most likely to kill me.

Host: Shamini Bundell

But you said we need to listen to people rather than try and convince them, so if people think that nuclear power is riskier than it is or if people don’t mind nuclear power as long as it’s not in their backyard, say, what’s the value in sort of consulting and listening to them? Won’t we just end up with, ‘Oh, well, maybe go and build that somewhere else.’

Host: Nick Petrić Howe

So, there is value in so far as you get different perspectives involved and, for the most part, nuclear energy has been proposed and commissioned by a relatively small group of people, and so you need a more diverse range of people and opinions involved. And if you contrast this with something like solar panels, for instance, so the solar panel industry has been a lot better at getting people involved, and now they’ve developed technologies that really help people do what they want to do whilst also providing energy. So, for example, there are now semi-transparent solar panels that allow people to grow crops underneath the panels whilst still getting energy, and so this sort of helps people and it gets those local people involved because the thing is, you’re not going to get nuclear power at all if you don’t have the buy in from the communities, and that could be on a local scale, it could be on a country-wide scale, but you really have to get their ideas and opinions in there so you know what it is they want to do. And another thing they say you can do as well is give people ownership of these things. Don’t have it as one big industry in one big place. You want to have it so that people have some sort of shared ownership, it’s like that’s not the nuclear power plant, it’s our nuclear power plant, and that can be really helpful in getting the buy in from people. And it could be that getting buy in makes people go, ‘Ah, we just don’t want it here,’ but we won’t know until we get those perspectives involved.

Host: Shamini Bundell

Well, energy and sort of climate change and all of these issues are obviously things that do affect everyone on the planet. No easy solutions, but I’m sure we’ll be chatting much more about these in future podcasts and future Briefing chats. Thanks, Nick. 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: Nick Petrić Howe

Just before we wrap up, I wanted to mention that we’ve got a new video on our YouTube channel – youtube.com/NatureVideoChannel. It’s all about how robots have been made soft to explore the deep ocean depths, and it’s voiced by yours truly. If that doesn’t give you a sinking feeling, be sure to check it out. We’ll put a link to it in the show notes.

Host: Shamini Bundell

That’s all for this week’s show. If you want to get in touch with us, tell us something nice, then we’re on Twitter. We’re @NaturePodcast. Or if you prefer email we’re podcast@nature.com. I’m Shamini Bundell.

Host: Nick Petrić Howe

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

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