The hunt for dark matter: The universe’s mysterious gravitational glue

In pursuit of dark matter, researchers are doing everything from burying vats of xenon deep underground to sending a balloon floating above the Antarctic. When will their creativity pay off?

Physics 8 February 2023

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Michael Kirkham

IF YOU happen to pass through Antarctica later this year, you could be greeted with a peculiar sight. Peel your eyes away from the penguins and you might spot something unusual floating in the sky: a balloon the size of a stadium. Trailing below it will be the latest mad-sounding experiment designed to look for the most maddening thing scientists have ever dreamed up – dark matter.

We reckon around 85 per cent of the universe’s matter is exotic stuff that doesn’t reflect, emit or absorb light, which is why it is called dark matter. The only force that this hypothetical stuff definitely deigns to interact with is gravity, as far as we know, which makes it incredibly difficult to detect. “When I gave talks on this in the 80s, I was telling people, ‘Oh, we’re going to figure this out in 10 years’,” says Katherine Freese, an astrophysicist at the University of Texas at Austin. Decades later, we are still waiting. “It’s obviously a harder problem than we realised.”

In the face of that hard truth, dark matter hunters have become ever more inventive. Attempts over the years to pin down what it is made of include burying vats of liquid xenon deep underground, measuring the straightness of lightning bolts, a plan to detect nanoscale explosions in minerals, examining ancient rocks for dark matter scars and checking the James Webb Space Telescope’s observations for “dark stars”. All of which raises the question: are some suggestions for dark matter searches a long shot too far? And at what point would we consider giving up the chase?

The first hints that …

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