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暗物质在哪里?|NaturePodcast

| 2019-06-24

 

又到了每周一次的 Nature Podcast 时间了!欢迎收听本周由Benjamin Thompson和Charlotte Stoddart带来的一周科学故事,本期播客片段讨论暗物质。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

For our first story this week we’re going to have a short history lesson. Now, not so long ago – in the 1980s in fact – it seemed like the big questions in physics would soon be tied up into a neat little bow. Astronomers had realised that the Universe must have a whole load of mysterious matter in it that we can’t see, which is called dark matter. At the same time, particle physicists were puzzling over why fundamental forces had such different strengths, and in particular why gravity was so weak. Handily, there seemed to be a solution to both problems in the form of hypothetical particles known as weakly interacting massive particles or WIMPs. So, researchers around the world set out in search of these WIMPs but more than 30 years later, every hunt for the wonder particles has returned empty-handed. Reporter Lizzie Gibney spoke to Gianfranco Bertone about the crisis that’s now unfolding in the field. She started by asking him what we’ve learnt so far about the elusive WIMPs.

 

Interviewee: Gianfranco Bertone

Well, we actually made an enormous progress in the sense that we’ve ruled out many, many possible models, and in particular there is a strong tension on the fundamental idea at the origin of the whole WIMP candidates, which was that these particles could explain at the same time the dark matter on very large scales in the Universe, but it could also address some of the most fundamental problems in particle physics. Now that we know that that connection is not that strong as we thought, we can generalise our searches, you know, search for particles which are much larger or much more massive than the particles we’ve searched for so far.

 

Interviewer: Lizzie Gibney

And so, the searches themselves have in a way been successful. They did what they were supposed to do, it’s just that what we were looking for isn’t there.

 

Interviewee: Gianfranco Bertone

Exactly, it was a very interesting hypothesis and we are testing that hypothesis. The fact that we’re not confirming the existence of these particles is not a failure of science, but it’s actually a triumph of the scientific method. We know that these particles do not exist in that particular form, and we know how to extend our searches in order to test the different hypotheses about the nature of dark matter.

 

Interviewer: Lizzie Gibney

Okay, so weakly interacting massive particles seemed like, theoretically at least, a wonderful idea. All the results have come out negative. Where do we go from here?

 

Interviewee: Gianfranco Bertone

Well, there’s a plethora of other possible explanations for the nature of dark matter. Very popular alternatives are so-called axions – particles that rise in the context of the physics of quantum chromodynamics. Then there are other particles called sterile neutrinos. So, these are again similar toneutrinos but have different types of interactions and they don’t interact almost at all with standard model particles. So again, these would be a perfect dark matter candidates.

 

Interviewer: Lizzie Gibney

What are some of the experiments that we should be doing to look for some of these new kinds of candidates? How will the hunt change as a result of that?

 

Interviewee: Gianfranco Bertone

I think we’re going to learn a lot in the next decade by exploring astronomical and cosmological surveys so just by looking at how matter behaves on very large scales. Does it interact with itself? Does it interact with other particles in the Universe? The other field of research that we can exploit is that of gravitational waves, and we can actually test really some fundamental ideas, for instance, is it possible that dark matter is made of black holes?

 

Interviewer: Lizzie Gibney

And there’s another slightly more radical explanation for dark matter that, certainly from a journalist perspective, seems like it’s been growing in prominence, which is that maybe dark matter doesn’t exist at all and we’ve just misunderstood how gravity works somehow. Is that an idea – I think they call it modified gravity – is that something that you’ve seen grow in prominence in the scientific world as well?

 

Interviewee: Gianfranco Bertone

Modified gravity is an excellent idea, as a matter of fact, in principle. Modified gravity was invoked as an explanation for the dark matter problem in the early 80s, at the same time when weakly interacting massive particles were proposed as an explanation for the very same type of phenomenology. The problem is though, a lot of additional evidence has accumulated and in particular we use the cosmic microwave background, this kind of relic radiation that is produced in the early Universe, and unfortunately modified gravity theories have very little to say about it.

 

Interviewer: Lizzie Gibney

So it does seem like dark matter is still likely to be out there somewhere, but we’ve been looking for it for 30 years now. What’s the mood like among physicists when negative results just keep coming up? How do people feel at the moment?

 

Interviewee: Gianfranco Bertone

I would say that there’s a growing sense of crisis in the field of dark matter studies, especially because we haven’t found the most popular candidates that we have searched for, for a number of years, for 30 years now, but I would argue actually that that’s a good thing for physics. The word ‘crisis’ has a very different meaning in science, in particular in physics, than it has in other fields, in economy and so on because it is precisely when there are crises that new opportunities arise and there’s room for big breakthroughs. I’m personally quite optimistic that we’re going to learn much more on the nature of dark matter in the next decade because we’re going to have a lot of new information and new experimental efforts that will provide complimentary information about the nature of dark matter.

 

Host: Benjamin Thompson

That was Gianfranco Bertone from the University of Amsterdam talking to Lizzie Gibney. Gianfranco recently co-wrote a Review about the search for darkmatter which you can find over at nature.com/nature.

 

Nature Podcast每周为您带来科学世界的全球新闻故事,覆盖众多科研领域,重点讲述Nature期刊上激动人心的研究故事。我们将话筒递给研究背后的科学家,呈现来自Nature记者和编辑的深度分析。在2017年,来自中国的收听和下载超过50万次,居全球第二。

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