社交媒体虚假信息可导致严重后果，平台可以遏制其传播吗？制作分子玻色-爱因斯坦凝聚体 | Nature Podcast

本期Nature Podcast为您带来，制作分子玻色-爱因斯坦凝聚体、社交媒体错误信息的传播、一种能杀死有害细菌而不破坏肠道微生物群的新型抗生素、拥有世界上最大基因组的小小植物，欢迎收听本期内容！

铷原子气体在玻色-爱因斯坦凝聚态出现之前、期间和之后的速度分布数据。峰值是在所有原子都占据最低量子能态时形成的。图片来源：National Institute of Standards and Technology/Science Photo Library

网上的错误信息导致了2021年1月6日的美国国会大厦骚乱。图片来源：Samuel Corum/Getty

Tmesipteris oblanceolata是一种罕见的叉蕨，这种植物没有真根和真叶。来源：Pol Fernandez

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Lizzie Gibney

Welcome back to the Nature Podcast, this week, creating a new kind of quantum matter…

Benjamin Thompson

…and how deep platforming users after the US Capitol riot stemmed misinformation on Twitter. I'm Benjamin Thompson.

Lizzie Gibney

And I'm Lizzie Gibney.

The quantum world is pretty mysterious. Not only do quantum rules seem so weird, but everything happens on a miniscule scale. One way to study this world is to make it balloon in size – using a Bose–Einstein condensate.

These condensates happen when atoms get really, really cold. If you remember the Heisenberg Uncertainty principle, you’ll know that the more we know about a particle's momentum, the less we know about where it is.

So if you cool down a bunch of atoms to close to absolute zero, what we know about their momentum becomes precise, but the boundaries of where the atoms could be get so big and blurry that they eventually overlap. You end up with indistinguishable atoms, all sitting in the lowest energy state – acting like one giant atom which follows quantum laws but is visible at a macroscopic scale and is precisely controllable.

These Bose–Einstein condensates — sometimes called BECs — can be used to study weird phenomena and create quantum technologies. But so far, physicists have mainly made them from atoms. They long to make them from molecules, stable molecules and ones that interact — which would massively expand the kinds of studies they can do.

Now physicists have done that for the first time. I spoke to Sebastian Will, a physicist on the team at Columbia University in New York and asked him what researchers can already do with Bose Einstein condensates.

Sebastian Will

Bose–Einstein condensates have been used to study quantum phenomena on a macroscopic scale. For example, it was possible to study superfluidity extremely well and also in the early 2000s, atomic Bose–Einstein condensates open the field of quantum simulation, for example, efforts have been made to study superconductivity in great detail using these systems. And again, we benefit a lot from the fact that, you know, everything is on an atomic scale in these systems, instead of an electron scale, electrons are a lot smaller. And this increased size, or these increased length scales help us to really look at the system in much more detail and try to understand it both better experimentally and theoretically.

Lizzie Gibney

So why do we then want to do this with not just atoms, but with molecules? How does that make this quantum playground even better?

Sebastian Will

You know, atoms are beautiful, you can cool them very well. But it also turns out that the interactions between atoms are fairly simple. Basically, atoms at these cold temperatures only interact when they are really sitting on top of each other. That is beautiful and straightforward to model theoretically. But in real life, you know, many systems, many, many-body, many-particle systems interact via long-range interactions. So for example, magnets interact at a distance, there is a sort of invisible force between them electromagnetic force between them. Or also in materials, electrons interact with ionic cores of the crystal lattice in which they are moving, which is a long-range of interaction. So long-range interactions are actually everywhere but in cold atomic BECs, they were not there. And one way to actually introduce long-range interactions into a system would be to cool molecules, and in particular polar molecules. Polar molecules are molecules which have a plus charge on one end and the minus charge on the other end. So there is electromagnetic interaction between the molecules. And this interaction happens at long-range. And if we were able to both condense molecules, we could really tap into this potential of realising fully quantum many-body systems with long-range interactions that we can use to simulate more interesting quantum phenomena. That was the dream already in the late 90s, early 2000s.

Lizzie Gibney

Seems like there's a really rich array of things that you'd be able to study if you had these super cold molecules in a Bose–Einstein condensate. So what's so hard about creating this state for molecules?

Sebastian Will

There is a saying in atomic and molecular physics, which is a diatomic molecule — a molecule with two atoms — is one atom too many. The internal structure of a molecule that's made out of two atoms is already so much more complicated. And when you make clouds of molecules, the molecules collide, and stick together upon colliding, and get lost from the sample. So in a cooling process, where you always need collisions between particles, so the temperature gets uniform in the sample, you actually start losing molecules and you lose the molecules faster than you can cool. And in the end, it wasn't possible to approach in temperatures that would lead to Bose–Einstein condensation.

Lizzie Gibney

And what kind of temperatures do you need? How cold are we talking about here?

Sebastian Will

We are talking about very close to absolute zero. It turned out now in our work that to get to a Bose-Einstein condensate, we needed to cool to below 10 nanokelvin. So that's just, you know, what is it–billions of a degree above absolute zero.

Lizzie Gibney

That is very, very cold. And so how do you manage to overcome that problem then? You needed to stop these collisions happening that created these reactions between the molecules.

Sebastian Will

So there we borrowed tricks that are possible once you are using molecules. We all know a very popular polar molecule, and that is the water molecule. We use microwaves very often in connection to water, basically, in our cup of coffee that we want to heat, we shine in intense microwave fields and they set the water molecules into rotation, which in this case, heat the coffee. So we can do this in a somewhat more precise and more sophisticated way. In our case, we are setting our molecules — in our case it's sodium caesium molecules — into rotation by exposing them to a microwave field that rotates and also expose them to a microwave field that oscillates. So this combination set the molecules for rotation in a very particular way, such that whenever two molecules collide, they start repelling each other. And this prevented the lossy collisions that have been a challenge to the field really for the last two decades. And really, that was the key to enable efficient cooling via evaporation, via evaporative cooling.

Lizzie Gibney

And how does that cooling work? What is evaporative cooling?

Sebastian Will

In our sample, we have a way how to selectively remove the hottest molecules in the sample. And we do this evaporative cooling process, and what remains is something much colder. And first, you may think, gosh, you need to throw away all your stuff to get cold and are you left with anything? Well, that is absolutely true. And that's why you know, you need these collisions between the molecules to be not lossy, because if you have these additional losses, you will never end up with a Bose-Einstein condensate. So preventing these collisions, these chemical reactions between the molecules is crucial to be left with cold molecules in the very end of evaporative cooling.

Lizzie Gibney

And how many molecules were you left with at the end of this process?

Sebastian Will

So we saw the onset of Bose–Einstein condensation when we had a cloud of 2,000 molecules and pure Bose–Einstein condensates we got was 200 molecules and these we can image.

Lizzie Gibney

And so that's something that just wasn't possible before to make this kind of condensate out of molecules?

Sebastian Will

Yeah, this was the first time this was observed.

Lizzie Gibney

So do you have any plans now of what you think you might like to do and what ways you might like to explore this system or the kinds of other quantum system you might simulate? It sounds like there are lots of options.

Sebastian Will

Basically, we now have a new system that really opens the door to a lot of new explorations. We would really like to leverage these long-range interactions between the molecules. And in analogy with water, we would actually be very excited to study crystallization in the quantum regime. Also, we expect the formation of so-called “quantum droplets”, where actually the droplets in contrast of water would be a superfluid. But there may also be technical applications that may come now into range. Because of Bose-Einstein condensate is sort of a pristine form of matter where we know what each molecule is doing, each molecule is actually completely identical in the same quantum state. So that is also an entry point to really get full single molecule control. And with single molecules, there have been already theoretical proposals for 20 years that you could actually use single molecules as qubits in quantum computing. And before I said, diatomic molecules are already one atom too many, but once you are actually able to control the internal quantum states of a molecule, it turns out that there are internal quantum states that are extremely long lived. That's exactly what you need for good quantum computing systems and that would be another really exciting direction to explore.

Lizzy Gibney

That was Sebastian Will from Columbia University in the US. Head over to the show notes for a link where you can find his paper.

Benjamin Thompson

2024 is a huge year for democracy, with around four billion people around the world able to vote in major elections. But the threat posed by the sharing of incorrect information — misinformation — looms large. These falsehoods, quickly and easily shared on social media, have been described as a serious threat to democratic integrity. But there are huge gaps in researchers’ understanding of how and why misinformation spreads online. This week, Nature is publishing a series of articles dedicated to those topics. One research paper looks at whether interventions by social media companies can actually stem the tide of misinformation. And to find out, the team investigated the events around a particularly troubling moment in recent US history. Adam Levy reports.

Adam Levy

These are the sounds of the US Capitol on January 6 2021, a day when US American politics changed for ever. It was the aftermath of the 2020 election, an election that Donald Trump had lost to Joe Biden. But Trump had been vehemently and without evidence, arguing that the election had been stolen. On January 6, this rhetoric turned to violent action as Trump's supporters stormed the capitol in an attempt to prevent the certification of the election results.

Chuck Schumer

I have never lived through or even imagined the experience like the one we have just witnessed in this Capitol.

Adam Levy

This is Chuck Schumer, leader of the Senate Democratic Caucus, commenting on the events of January 6 later that same day after the insurrection had been overcome.

Chuck Schumer

This temple to democracy was desecrated: its windows smashed, our offices vandalised. The world saw Americans elected officials hurriedly ushered out because they were in harm's way.

Adam Levy

And for political scientist David Lazer of Northeastern University in the United States, these events had profound implications well beyond the day in question.

David Lazer

So that gets to the very core of what democracy is about if people don't believe election results, and you can't really have a legitimate transfer of power. Really, as an American citizen, I was–I was shocked by the events of the day as they were unfolding.

Adam Levy

And while many factors and events led up to January 6, a lot of attention turned to social media, and in particular, Twitter. Although less widely used than some other social media, Twitter had established itself as having something of a town square function, with many politicians and journalists using the platform. And researchers like David saw Twitter as playing a pivotal role in building momentum towards the attack on the Capitol, in the way that it was used both by Trump's supporters, and by Trump himself.

David Lazer

He had called for a rally on January 6, he used the language in that tweet “will be wild.”

Adam Levy

A major cause for concern was the sharing of misinformation on Twitter, in particular around the validity of the election results. And so, in the days after the storming of the Capitol, Twitter took active steps to combat misinformation spreading on the platform.

David Lazer

It eventually culminated in a decision to deplatform a fairly large number of accounts, I think around 70,000 accounts that were central in sharing election misinformation. You know, the question I was asking myself was, how big of an effect did it really have?

Adam Levy

These actions at Twitter gave David and his team a unique opportunity to peer behind the curtain and attempt to answer this question.

David Lazer

You know, what platforms do is often pretty opaque, they're doing stuff, but you don't know what buttons they're pressing, and you don't know what days they're pressing them on. In this case, we knew what days and we knew what button.

Adam Levy

To find out what effect pushing the button had, David and the team analysed the activity of over half-a-million Twitter users during the election period. This showed that misinformation sharing had indeed followed an unusual pattern during the 2020 election cycle. In contrast to the 2016 election, it remained high even after Americans went to the polls, as claims that the election had been stolen circulated. Within the group of users the team investigated, just over 1,000 were deplatformed following January the 6th. While a small number, they were responsible for almost a quarter of the misinformation links shared in the total sample group the previous month. Twitter's sudden deplatforming of a small group of major misinformation sharers was followed by a dramatic drop in misinformation on the platform. In part, this was due to those spreaders no longer being able to tweet. But that wasn't all.

David Lazer

There had a secondary effect that the accounts that followed those deplatformed accounts shared less misinformation. And then the third effect was that a lot of the people who behaved a lot like the deplatformed accounts left and one can guess that their inference was that Twitter was no longer a friendly platform to them.

Adam Levy

Overall these three processes saw the share of misinformation roughly halve among the sample group. But how can we be confident that these effects were caused by Twitter's moderation decision? After all, even at the best of times, there are confounding factors. And the period following January 6, was by many definitions, not the best of times. And so the author's tried to unpick why followers of deplatformed accounts ended up spreading less misinformation.

David Lazer

They did share less misinformation. But that could have just been the events after January 6, right? Everyone was shocked and maybe they said, oh, you know, I shouldn't share stuff like this. So what we did was we compared those individuals who follow the deplatformed accounts to other individuals who did not follow those accounts and what we saw was for the first group that followed those deplatformed accounts, the amount of misinformation that they shared dropped quite a lot relative to the accounts that did not follow the deplatformed accounts,which suggests that the change we observe is indeed causal.

Adam Levy

For Emily Thorson, a political scientist from Syracuse University in the United States, it's important to be cautious about how strong a causal link we can draw between the deplatforming and the drop in misinformation. Still, though, the results could help guide decisions that social media platforms make in the future.

Emily Thorson

This does give us some evidence that if platforms wanted to, they could decrease the amount of misinformation or other types of harmful content on their sites.

Adam Levy

Emily, who didn't work on this study, although she does collaborate with David, feels that there are still huge unanswered questions on how social media interventions work, or could work in the future.

Emily Thorson

I think it would be potentially more effective to look at who are the people who are either spreading or seeing lots of misinformation? And how do we target interventions at them? So who are these people and what's driving them, right? What are the factors, the offline factors that are pushing them to share more misinformation? Whether that's media exposure elsewhere, like on television or radio, whether that's interpersonal contact, et cetera.

Adam Levy

Whatever we learn about the spread of misinformation on social media, our societies still need to decide what to do with that information. For now, in many contexts, decisions are left up to the management of social media companies. And since the events investigated by this study, Twitter's processes have changed dramatically. Now overseen by Elon Musk, the platform has rebranded as X and has dramatically scaled back moderation efforts. How to strike the balance between protecting users and safeguarding free speech remains a topic of fierce debate.

David Lazer

The question really should be: where does society step in? And, you know, that's a hard one. I think this is one that modern policymakers are wrestling with.

Adam Levy

Of course, different policymakers will come to different conclusions in different contexts. But Emily warns that we shouldn't assume that social media is the only, or even the primary, way that people encounter misinformation.

Emily Thorson

It is still the case that most of the information that people get about politics does not come through social media, it is coming through television, it is coming through radio, it is coming through interpersonal conversation.

Adam Levy

This chimes with the view that overall exposure to, and sharing of, misinformation online may be overstated. For example, in this work, only 7.5% of users shared any misinformation during the study period. Even so, social media does still play an important role in our lives, a role that is constantly evolving. And research like this could help sculpt the decisions we make about what our social media looks like in the future.

David Lazer

I am still concerned about the future. That we haven't as a society really figured out how to manage the whole content moderation. It is a legitimately difficult question, but I don't think we've come up with an answer that protects us going for forward.

Benjamin Thompson

That was David Lazer, from Northeastern University. You also heard from Emily Thorson from Syracuse University. To read David’s paper and more Nature’s articles investigating misinformation, head over to the show notes for some links.

Lizzie Gibney

Finally on the show, it's time for the Briefing Chat where we discuss a couple of articles from the Nature Briefing. Benjamin, what have you been reading this week?

Benjamin Thompson

Well, Lizzie I've got a story about a new antibiotic, okay. And it's one that kills deadly bacteria, but potentially spares the gut microbiome, and I read about it in Nature.

Lizzie Gibney

That sounds really important, because that's a massive problem right with antibiotics is they do a great job when you need them, but they end up destroying your microbiome.

Benjamin Thompson

Absolutely right. So they are a medical marvel antibiotics. But yeah, on the podcast a few weeks ago, we heard someone describe the gut microbiome as like a “jungle”. And sadly, antibiotics are kind of indiscriminate. They're kind of a forest fire and that can really upset the gut microbiome that's so important for so many different things, for digesting food and for the integrity and health of organs, and even potentially, for the health of immediate offspring, right. So really, really important.

Lizzie Gibney

I find we have like a story every week on something new about the microbiome and how important it is. So we might only know half of what’s essential about it.

Benjamin Thompson

The list is getting longer and longer. But what happens then, so we need to treat pathogenic bacteria, bad bacteria, okay, we do that with antibiotics. And in particular, there’s this one broad group of bacteria called Gram-negatives, okay, Gram-negs they're sometimes called. And within this group, there are some really nasty bacteria. E. coli, Klebsiellas, your pseudomonads and some of these are resistant to common antibiotics, and very troublingly, some are resistant to multiple antibiotics. So we really need to work out, you know, new ways to treat these bacteria and Gram-negatives are particularly tricky, and that's where this new work comes in.

Lizzie Gibney

Okay, so what is it that they've done or found?

Benjamin Thompson

Well, in this particular case, they've developed an antibiotic that they call Lolamicin. Okay, now, ‘lol’ doesn't mean ‘laugh out loud’ in this case, it means ‘localization of lipoproteins’. Okay now, the ‘lol’ pathway is really, really important to Gram-negative bacteria, okay, it’s what they use to put these things called lipoproteins in their outer cell membrane, okay, so without it, they can't make the membrane properly. And so what Lolamicin does is it kind of selectively targets this pathway and it seems to be quite effective at killing, inverted commas, bad bacteria.

Lizzie Gibney

So in that way, it targets just the bacteria we want it to target.

Benjamin Thompson

Yeah, that's right. So they tested it against, well, over 130, multi-drug resistant strains in a dish, and it seemed to kill those. And in mice that developed bloodstream infection after exposure to these antibiotic resistant bacteria. All these mice survived after been given Lolamicin while 87% of those who didn't, died within three days. So quite effective, but in mice double underline at this point. And also, lolamicin treatment didn't seem to cause any observable changes in the gut microbiome and spared mice from C. difficile infection. And this is of course, an opportunistic pathogen that can sometimes takes hold– take hold in the guts after antibiotics are used.

Lizzie Gibney

Wow. So I guess we still need to figure out if there are other side effects, you know, there's a long journey to it being used clinically?

Benjamin Thompson

Oh 100%. And I think the gap between you know, mice and humans is a pretty big one. And of course, it's a long road to understand exactly how effective it is, if any resistance arises. But I think it's worth saying there is a desperate need for new antibiotics, particularly ones that target these Gram-negatives. Okay, now, the golden era of antibiotic discovery was in like the 40s, and 50s, and 60s, and since then, even recently, it's really sort of a trickle of new ones that have come through. And partially, you know, that's because it's quite tough to bring these things to market. And also, there's not a huge amount of incentive for companies because resistance to antibiotics develops. So if your drug becomes ineffective within a couple of years, there's no point spending countless millions of dollars. So I think this is an interesting one, like, it's really important that we have these candidates, and there are others that are sort of working their way through the preclinical studies. And so it remains to be seen how far this one will go. But say, you know, potentially a good news story.

Lizzie Gibney

Wow, it's nice to have a good news story from time to time. I think I've got what is kind of a good news story, an interesting news story. Mine is also in biology so I'm well outside of my comfort zone here. This is about discovering, this is a record breaker, very tiny record breaker, the organism with the biggest genome ever discovered.

Benjamin Thompson

Alright, okay so when we talk about genomes, then we're talking about its genetic A's, T's, G's and C's. I suppose we've talked about bacteria there, they've got pretty small genomes, humans have got a pretty big one. But what's the record holder then?

Lizzie Gibney

It’s a plant, which, I mean, even just that kind of astounded me in the first place. So we're talking about 160 billion base pairs. So that's bigger than the human genome, do you know how much bigger?

Benjamin Thompson

Oh, I'm gonna say that's got to be an order of magnitude bigger?

Lizzie Gibney

50 times bigger.

Benjamin Thompson

Right.

Lizzie Gibney

So that's a lot bigger. So this is also a record so it's 11 million more base pairs even than the previous record holder, which was also another plant. Which no dissing plants, but I haven't even written down that plant’s name. But it's really fascinating to study because, of course, this plant you know, it looks if people know rosemary, it looks like a little spree of rosemary, but its actually native to New Caledonia and surrounding areas in the South Pacific. But it's just a little fern. And only a very small proportion of its DNA is actually used to code proteins. And so there are a couple of big questions that scientists have, you know, how does it find the bits it needs when it's got a rifle through 160 billion base pairs?

Benjamin Thompson

Right.

Lizzie Gibney

And how is it ended up with so many if it doesn't use them? You know it normally it takes a lot of resources, it takes effort to keep replicating your genome. And why does it do it? If it doesn't need it?

Benjamin Thompson

I guess in a bunch of organisms, there is some redundancy in terms of genes and pseudogenes and what have you, but this looks like there is an awful lot of it.

Lizzie Gibney

Absolutely loads. And so the answer is we don't know yet. But there's some speculation and the answer is great, but also as Max Kozlov, my colleague here at Nature, wrote in this story, it might be quite boring answer. Which is that it might be that it's just not very detrimental to this particular plant, because it maybe doesn't have a lot of competition. It’s in this quite stable environment and so maybe it can just get by replicating this enormous genome because it doesn't really have that much pressure on its resources in that way. So it's just accumulated over time, and it hasn't had the evolutionary pressure to get rid of it.

Benjamin Thompson

And so, we have this record breaker then, is this just one of these like, well, that's a strange thing okay, cool, let's move on, or is there more to be done with this genome?

Lizzie Gibney

Well, there is definitely more to be done. So I think one thing is they– they would love to sequence it.

Benjamin Thompson

So, I mean, I guess they know how long it is then, but they actually want to know the exact order of where the different bases are. And that's gonna be a big job, right? Because that's a big genome?

Lizzie Gibney

Well, that's it, you've got 160 billion of these things, and it's just sounds like an enormous puzzle. So current methods just aren't up to scratch, we think. So, you know, finding an enormous genome like this helps us to think well, maybe we should be finding better ways to sequence. And also, researchers want to understand, does having an enormous genome like this have an effect on organism? Does it help it grow, flourish, deal with climate change, maybe be resilient, that's independent of your natural DNA sequence? It raises a lot of questions, and just sounds like a fascinating, if teeny, tiny plant to study.

Benjamin Thompson

Well, always lovely to have a record breaker on the show, and congratulations to that plant, I suppose. Let's leave it there for this week's briefing chat. And listeners, for more on those stories and for where you can sign up to the Nature Briefing to get more like them delivered directly to your inbox, check out the show notes for some links.

Lizzie Gibney

And that’s all for this week, as always keep in touch with us on X, we’re @NaturePodcast, or send an email to [email protected]. I’m Lizzie Gibney.

Benjamin Thompson

And I'm Benjamin Thompson. Thanks for listening.

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