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十年前，瑞士欧洲核子研究中心（CERN）的科学家们宣布他们发现了希格斯玻色子存在的证据。希格斯玻色子是早在约60年前就被认为存在的一种基本粒子，由研究人员在大型强子对撞机（LHC）中通过粒子碰撞发现的，是构成标准模型的关键部分。而标准模型是物理学家对构成宇宙的基本亚原子粒子以及它们之间的基本力的最佳描述。为了庆祝这个粒子的十岁“生日”，Benjamin Thompson采访了两位对粒子物理非常了解的人——《自然》的记者Lizzie Gibney和物理学主编Federico Levi——以了解这一发现在当时意味着什么，以及关于这一神秘粒子还有哪些问题有待回答。欢迎前往iTunes或你喜欢的其他播客平台下载完整版，随时随地收听一周科研新鲜事🎧。 音频文本： Host: Benjamin Thompson This week marks a momentous milestone for physics. Ten years ago this week, scientists at CERN in Switzerland announced that they’d found evidence of the existence of the Higgs boson – a fundamental particle first theorised to exist nearly 60 years earlier. Discovered by researchers smashing particles together in the Large Hadron Collider (LHC), the Higgs boson is a key part of the standard model – physicists’ best description of the elementary subatomic particles, and the fundamental forces between them, that make up the Universe. To celebrate the particle’s tenth birthday party, we got two people together who know an awful lot about particle physics – Lizzie Gibney, a senior reporter for Nature, and Federico Levi a senior physics editor for the Nature journal. We sat them down to reminisce about what the discovery meant at the time, and what questions are left to be answered about this mysterious particle. 《自然》Editorial：Particle physics isn’t going to die — even if the LHC finds no new particles 长按并识别右方二维码，阅读全文→ Lizzie Gibney Fede, can you remember where you were, what you were doing when the Higgs was discovered? Federico Levi I definitely do. Yeah, I was still doing my PhD, actually. We crowded the main room of the physics department to look at broadcast in real time because people knew that something was in the air. And we were all there and it was amazing. Lizzie Gibney I heard people camped outside the lecture theatre at CERN, like from the night before, to be able to actually fit into that room. Federico Levi That must have been incredibly exciting to be there on site. I wasn't in Geneva, but the buzz was palpable. And everybody was texting one another going like, 'This is incredible.’ So, it was quite a momentous moment. Lizzie Gibney Yeah, I was a reporter at the time, but not here at Nature, and I was writing for a publication that was more about policy rather than like research itself. But I remember, I was actually at a scientific event at the Royal Society in London, and there was so much buzz that evening. And because I had actually worked previously at CERN as a kind of staff writer as an intern, I had lots of questions from my friends and family, so they were being pinged at me all the time. It was great. It was kind of the first moment really that particle physics felt like it had broken through in that way. It was a subject for people on the street to talk about. But I do remember as well that, when they made the announcement, I just said now that it was a discovery, but they were quite cautious at first, weren’t they? They said we found a Higgs-like particle or something like that. They didn't say, 'We've definitely got the Higgs boson.’ Why were they so cautious? Federico Levi As you know well, physicists tend to be quite cautious, right. And I think that deep inside their hearts, many people felt differently than what they actually said. But the evidence that was presented on that day was the presence of a particle with a certain mass. And it was a particle that was definitely off the chart. It was not corresponding to any particles that we knew already. Lizzie Gibney It was new. Federico Levi It was a new particle, exactly, with a mass that was exactly in the range that people expected the Higgs boson to be. And so, people were like, 'That seems to be the thing we're looking for but clearly there is so much more to characterise about this,’ and definitely people have been busy since. Lizzie Gibney Yeah, so maybe we should tackle a bit of what it actually is because we've heard about how grand a discovery it was, but why was it so important to find the Higgs? Federico Levi Well, first of all, I wasn't around back when other particles conjectured by the standard model had been detected, and I could imagine that the excitement was similar. But in a way, the Higgs is so fundamental that it has almost a different status. It was sort of like something that had to be there for everything else that we've seen to make sense. It was really sort of the keystone that holds together a big mathematical construction – that is the theory of the standard model. And so, it's amazing that that particular thing, which comes from a very sort of human idea, which is the maths behind it, actually exists. To me, it’s mind blowing, right, and I think that many people felt that way. Lizzie Gibney I mean, people might have heard of a boson being something like a photon, but photons don't have mass, and that's the electromagnetic force. And then we've got the weak nuclear force, which has bosons, which do have a mass – they’re the W and Z bosons. And so, if I'm right, this is what the Higgs mechanism was doing, was giving some maths that would explain those two phenomena and how they could both equally fit in the standard model. Federico Levi Yeah, that's exactly it. Basically, how these two different forces could be different representations of a bigger structure, despite them being so different from a physical perspective. Lizzie Gibney And for that we need the Higgs field, which is this idea that Peter Higgs, but also a whole alphabet of other physicists, helped to discover and to theorise. So, this field exists that gives other particles mass, and the boson then, how does that relate? The boson isn't what's giving the mass, right? It's the field. Federico Levi The boson is the excitation of the field. So, in a way, if the field is there, the way you see it is through the corresponding boson. So, the Higgs boson is what you can use to actually sort of probe the field, which is, as you said, the fundamental entity that gives then masses to the rest. Lizzie Gibney And the way then that it works is that the more a particle interacts with the field, the more mass it has. Is that the general idea? So, when you have a really heavy particle, it's because it's reacting in a strong way with the field. Federico Levi Yeah, that's exactly it. I think that, like a mathematical perspective, what we call mass is effectively a drag that the particle feels through the Higgs field. Lizzie Gibney That's cool thing to mess with your brain, isn't it? So, as you said, Peter Higgs came up with this idea 50-60 years ago, a long time ago. And in terms of what we’ve learnt so far, I mean, the main thing is just how well it does fit with the standard model. Federico Levi It is fitting perfectly. And I think that that's, yet again, a moment that you almost want to pause and consider how incredible it is that something that was theorised 60 years ago, it's exactly been revealed in experiments. So, our description of reality is perfectly matching what nature is throwing at us. Nobody said that this should happen. Lizzie Gibney And so, we're ten years in. What did it mean for you in terms of papers and publishing? And how did it change physics in that way? Federico Levi It's an interesting question because, at some level, there is something about these huge discoveries that seem to change everything, but they don't really change that much in the end because, if you browse particle physics journals or articles, you will see articles that are very similar to the articles that used to be around, just with the Higgs in it, right. And that's actually, it's so deep, the difference, and yet so almost unnoticeable because, basically, most of the research these years has been focused on understanding the Higgs’ interaction with particles. And so, several results are how can we measure this better? What have we measured so far? Here's an idea on how to increase the precision on measuring this interaction with that. Essentially, particle physics got down to it and like they really kind of get going applying the expertise accumulated over decades of work with other particles to the Higgs. Lizzie Gibney So, the discovery was kind of like a starting gun and then you're like, 'Oh, actually, we have to pin down all its properties and all the Higgs’ interactions and figure out how all those results then fit with theory.’ But I assume there are still a lot more questions that physicists want answered. Federico Levi Absolutely. To start with, given that the Higgs interacts more with heavier particles, we have seen only the interaction with the heaviest particles, whereas the interaction between the Higgs boson and the lighter particles, such as the ones that actually make up the world, such as electrons, protons and neutrons, it is much harder to realise this experimentally. And so, this has not been really observed yet with enough statistics to make any estimates. So, that's definitely something that the community would like to explore next. And this is clearly an effort to, first of all, check whether the standard model, as annoyingly accurate as it's been so far, keeps being so annoyingly accurate, if you want. But also, the Higgs boson is one of the many possibilities that could be happening to explain what we've seen. So, there are a number of conjectures that, if you want to set the stage for beyond the standard model physics, that involve the Higgs boson in some way. There could be more Higgs bosons or some conjectures are whether the Higgs boson is a composite particle, so whether it's made of something else. Lizzie Gibney So, it's not fundamental. Federico Levi We have no idea. There are basically theories for everything you can imagine, right? But then the experimental evidence needs to be accrued. So, there is so much that we need to understand. Lizzie Gibney And so, how big a deal is the discovery of the Higgs? if we look at, like the history of physics, of science, how far up there is it? Of course, it's part of the standard model. There have been lots of different inputs to the standard model over the years, but it is also that last missing piece that was discovered. Federico Levi Well, I was hoping you wouldn't ask me this question, but here I am. Lizzie Gibney Maybe personally because that’s the other thing is for you in your life, it probably has been a bigger deal than the discovery of relativity was because you weren't around. Federico Levi That is fair. That is accurate. No, I think it's basically up there to be honest because, to an extent, this is the equivalent of one of those first, early experiments that actually confirmed the theory of relativity. Because at some level, the standard model, the paper by Peter Higgs and all the other researchers of that time, remain quite bound to the realm of physics literature, until an experiment, bang on, realises that these people were right. And this is something so fundamental about the workings of nature, similar to relativity in a way, that is really like, 'Okay, this is how the world works.’ So, these moments come very rarely in human history, so I would say that it's definitely up there. Don't ask me to put it before or after relativity, but I would say it's up there. Lizzie Gibney We were quite lucky to be around to see it. Federico Levi Absolutely, absolutely. Well, let's hope there is something else coming. Lizzie Gibney That's true. This might not be the end of the story. Host: Benjamin Thompson Lizzie Gibney and Federico Levi there, discussing the Higgs’ tenth anniversary. 《自然》Editorial：Particle physics isn’t going to die — even if the LHC finds no new particles |
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