‘One of the biggest discoveries in science’: have scientists found dark matter?
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It's one of the biggest mysteries in science, an elusive substance which has been hunted by physicists for decades, and now a tantalising piece of evidence. Maybe a finding that could unlock a new understanding of our universe. So today, have scientists finally caught a glimpse of dark matter? From The Guardian, I'm Madeleine Finlay, and this is Science Weekly.
Ian, we're here to talk about a potentially very exciting finding for physics about dark matter. But before we get onto the finding itself, let's talk about the background. What do we need to know about dark matter?
Dark matter is this mysterious, invisible substance that seems to clump around galaxies. Now, it doesn't emit, absorb or reflect light or any other electromagnetic radiation. That makes it really difficult to see. It's invisible, but it makes it also very hard to detect. And the way we really know about dark matter is through observations of the sort of gravitational effects it has on other things. And what we can tell is that dark matter seems to form this... It's often called a cosmic web. It sort of seems to form a kind of structure for the universe, okay? Now... Two people who are really key in getting some understanding of dark matter out there. The first is a guy called Fritz Zwicky. He was a Swiss-born astronomer.
And in 1933, he started looking at clusters of galaxies. And he noticed that there wasn't enough visible matter in these clusters of galaxies to prevent the galaxies from just flying apart. And he said, oh, maybe there's this stuff called, he called it dunkle materiae. That didn't have a massive impact at the time. But about 40 years later, in the 70s, a US astronomer called Vera Rubin, she looked at individual galaxies. So she zoomed in on individual galaxies and looked at the speeds of the stars, especially around the periphery of those galaxies. And she worked out that the speeds of those stars at the edges of those galaxies just didn't make sense unless there was... some other matter there that wasn't visible, but that was exerting a gravitational force on those particles.
And so now the sort of thinking is that galaxies are forming and exist within these kind of clouds of dark matter.
So you could say that right now dark matter is a set of observations with a sort of enigma at their heart. But why is figuring this out such a holy grail for physicists and people who study the universe?
Dark matter is thought to make up about 85% of the matter of the universe, okay? That would leave, you know, what we call normal matter, the stuff of you and me, making up about 15%. It's extraordinary that we don't know what makes up the vast majority of the matter of the universe. That is staggering. And so to understand this is an enormous question in physics. It's all clearly a bunch of particles that are unobservable to us, at least directly, but we don't know what's there. And that is super intriguing.
So you said they're unobservable, they're non-interacting. Presumably this is why it's been so hard to find out what exactly dark matter is.
Yeah, so not only is dark matter invisible, It also sort of barely interacts with other matter. So it streams directly through you and me, the stuff of normal matter. And so it's really hard to detect. The other thing that makes it tough to find is that if you're looking in a detector for dark matter, you know, you're looking for incredibly rare collisions or interactions between particles. The thing is, particles are interacting all the time. And so you have these huge, physicists call them backgrounds. You have background noise, essentially, from other particles interacting. Radioactive decays, particles coming in from the solar wind, from space.
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