The end of darkness?

02 June 2015

Interview with

Dr Kathryn Freese, NORDITA

Scientists have been looking for Dark Matter since Fritz Zwicky theorised it nearly A light at the end of the tunnel100 years ago! And whilst scientists have developed clever way that we could detect it, we're not much further forward that Zwicky: We don't know what it is, we don't know where it came from, and at a fundamental level, we're still figuring out what dark matter is and isn't. So why continue? Why is finding dark matter still so important? Graihagh Jackson put these questions to Dr Kathryn Freese, physicist from NORDITA...

Katherine - The dark matter problem is almost 100 years old. So, this is maybe the longest outstanding problem in all of modern physics. So, this is a big one and we really want to nail it. The good news is that we have ideas for what it could be and we think that discovery is around the corner. So, I'm predicting in the next 10 years that we'll know.

Graihagh - That's the good news.

Katherine - That's the good news.

Graihagh - What don't we know? What's the bad news?

Katherine - Well, the only thing we really know is that it has some kind of gravitational pull, It yanks things around, You can see a lot of that going on, but we don't know what it's made of. The fear in the back of our minds is always, what if we're just really heading in the wrong direction? What if we are just completely missing the point?

Graihagh - If we are wrong, that sounds like a pretty scary idea because surely, this underpins many phenomenon we observe in the universe.

Katherine - Yeah. Well, so, the nightmare scenario is - let's go back to Aristotle and Ptolemy where they had the idea that everything is revolving around Earth. But the picture was kind of all wrong and it took thousands of years to correct that. So, our worst nightmare is we're somehow making an epicycle mistake and that some brilliant kid - I don't know - 20 years from now or 50 years from now is going to come along and say, "Hey, rethink this entirely". If it's 50 years from now, I won't be around. So, that's the worst nightmare, the worst fear. But the reason I say I don't believe that about dark matter is because we have so many pieces of evidence from so many different directions that it would be very hard to explain in terms of anything else. So, I'm pretty convinced about the dark matter that it's real.

Graihagh - You say you're pretty confident that we'll be able to find it in 10 years time, what makes you so confident that that's a possibility?

Katherine - We have really good candidates, these WIMPs and we have experiments that are doing a really good job of searching for them. In fact, I played a role in pioneering these studies in the first place and that was 25 years ago. We did some calculations if the WIMPs that are in the galaxy, the calculations of how they interact with ordinary matter and we made predictions for what the detector might be able to see. In fact, because of our work, they started building these detectors all over the world, these underground direct detection experiments. And the sensitivity that we initially said you have to have is, wow! They are a thousand times better at this point than we ever imagined they would be. So, these experiments are getting really good! They're really sensitive! And some of them are seeing strange anomalous results. I don't know. Maybe that's nothing. Maybe it's just background, but I'm hoping that there's something to some of these strange anomalies and maybe they're hinting that we're resolving this problem. So, I guess I believe in this type of candidate as being really well-motivated. The experiments are really capable at this point of seeing something and some of them maybe already are. So, I'm hopeful for the near future.

Graihagh - Given that there is so much evidence for it and it would obviously be a very exciting prospect to find it - 100 years in the making - how would it affect our knowledge of the universe?

Katherine - So, imagine the ancients be ancient Greek, go back to cave days. They must've wondered what is out there. I mean, that's what makes us humans. That's who we are as a species. We're curious and we want to understand our surroundings. That's why we've been successful as a species. So, I think this is kind of the burning desire to understand - my God! - the bulk of what is around us, the bulk of the universe. So, I think answering this big giant question, that's revolutionary and that's super important all by itself.

Now, on the practical side of things and this is why they pay us, it's likely that there will be some consequences for our daily lives. Traditionally, science is funded at the fundamental level because people think there can be serendipitous discovery of something that will change society. That could happen either from the detectors. In building the detectors, you might find some new technology that is really important for, I don't know, curing cancer or something. Who knows? Or once we know what the dark matter is, I don't know what the consequences will be. Will we get some new kind of heat source better than sending more carbon dioxide up there? so, the beauty of fundamental science is that it's intrinsically important. It's intrinsically interesting, but it also tends to change our lives.

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