Are we any closer to detecting dark matter?

0:00Dark matter is one of the strangest puzzles of modern science. This invisible substance makes up about 85% of the total matter in the universe much, much more than the stuff we can see, yet despite dark matter's abundance, scientists still have not directly detected it after decades of searching. One of the experiments built to detect it sits in an old gold mine about a mile underground in South Dakota. And scientists there just announced a strange event they cannot explain, renewing excitement around the hunt for dark matter. Here, to unpack it all with us is Priyambada Natarajan, chair of the Department of Astronomy at Yale University. She's a dark matter expert, but wasn't part of the experiment. Welcome. Thank you, delighted to be here. What is it like to be an expert in something nobody has ever verified? Well, you know, all my work is relevant to the invisible universe. So you can ask what does one do with a lifetime dedicated to the things that are not seen?

1:03Well, they're not directly seen, right? So that's what's amazing about dark matter. Even though dark matter itself does not emit absorb or reflect light, which is how we actually light is the cosmic messenger. And because it doesn't interact with light, we don't actually directly see it. But we see it indirectly. Dark matter, for example, because it's matter, it has gravity. And so it impacts the motions of objects, right, of stars that are visible matter. And that's how we infer its presence. And the challenge has always been, like, we see this on astronomical scales, right? It's smeared lightly everywhere in the universe, but lumps in many places, like around galaxies. Yeah. But making the connection to what particle it might be, what subatomic particle it might be, that has been the challenge. So you were not directly part of this experiment, but I have to imagine you were paying very close attention. Can you briefly explain what they saw in this underground dark matter detector?

2:04Yeah, the experiment itself is quite remarkable, right? It's the Lux Zeppelin. It's one of the world's most sensitive dark matter detectors. And basically, it's a vat of xenon. So xenon is one of those inert gases that can also exist in liquid form. And one particle, something, seems to have struck xenon nucleus. And the operator word is one, right? So it's just one event. But it hit it unusually hard. And so they cannot explain this with radioactive particles, neutrons, neutrinos, you know, all the other kinds of effects, you know, detector effects, etc. So they found this event, but it's not significant, statistically, at the level that scientists feel convinced that it's actually a discovery. It's not a discovery. Why is it so intriguing, though? Like, what is it about something, struck something in here that has everybody so curious?

3:08The thing is, it's completely unexpected. This kind of interaction. So we have a lot of models. There's a landscape of models of what all dark matter could be, right? You know, and we have a zoo of particle candidates, and we have made predictions for what, if at all, and ever we would see them, how they would interact. And so this was a real plaque. So the simplest dark matter models, right? They predict a lot of gentle collisions and a fewer real hard, you know, high energy twacks. But here, we didn't find any gentle collisions. We just found one plaque. Okay. So that's really, really bizarre because that tells you that this is a very special kind of particle. So what happens next? So I guess we all get busy, both experimentalists and theorists. The experimentalists actually have a lot more data that they haven't analyzed yet.

4:08So this event was detected about two years ago. So they have that data in hand, and they're going to continue running the experiment. And all of us model builders and those interested in theoretical ideas are going to get really busy coming up with new ideas. Let me ask you to theorize hypothetically if we were to crack the code and figure out what dark matter is made up, which I know is like 80 steps down the line from what we're talking about right now. How would that change our understanding as best as we can guess of how the universe is constructed? I think it would be utterly transformative. It would be the most radical discovery of not just this century, because dark matter dominates the matter inventory of our universe, right? And as you mentioned, right, only about 85% of all the matter in the universe is dark matter. And the stuff that we are made of is 16%. Everything in the periodic table, right? We're like, you know, we're a bit player in the matter game, right? So this is what everything else in the universe is. This is like suddenly knowing what the universe is really made of, right?

5:14I mean, it really would give us some much better grounding on our place in the universe, right? Like how we really came to be. Priyambada Naderajan of Yale University. Thanks so much. Thank you so much, God.