The wonder particle: How axions could solve more than just dark matter


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Colin Reid

IN 1977, physicist Frank Wilczek took a walk that would change the course of particle physics forever. “On that walk, I had the germs of two really good ideas,” he recalls. The first was how a theoretical particle, later dubbed the Higgs boson, might interact with other particles. This would be how the Higgs was found decades later. The second idea, however, has taken a little longer to catch on.

Wilczek had imagined a way that very light – essentially massless – particles could be made. He talked to his colleague, the late Steven Weinberg, who had been thinking along the same lines. Together, they predicted a class of particles we now call axions.

Weinberg was optimistic, convincing Wilczek, now at the Massachusetts Institute of Technology, that axions would be easy to find. But nearly half a century later, we are still looking. In the intervening years, interest in axions – largely fuelled because they could be the hard-to-find dark matter that makes up 85 per cent of the matter in the universe – dwindled in favour of other explanations.

Today, amid our failure to track down dark matter and a slew of theoretical and experimental breakthroughs, axions are resurgent. “They’re very much back in fashion,” says Wilczek.

And now, there is far more than the mysterious nature of dark matter up for grabs, because axions offer a solution to a whole host of cosmological mysteries, including the elusive dark energy thought to drive the universe’s expansion. They are, in short, the particles that could solve the universe.…

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