Our best theories of physics imply we shouldn’t be here. The Big Bang ought to have produced equal amounts of matter and antimatter particles, which would almost immediately annihilate each other, leaving nothing but light.
So the reality that we are here – and there seems to be very little antimatter around – is one of the biggest unsolved mysteries in physics.
In 2001, Tanmay Vachaspati from Arizona State University offered a purely theoretical solution. Even if matter and antimatter were created in equal amounts, he suggested that as they annihilated each other, they would have briefly created monopoles and antimonopolesMovie Camera – hypothetical particles with just one magnetic pole, north or south.
As the monopoles and antimonopoles in turn annihilated each other, they would produce matter and antimatter. But because of a quirk in nature called CP violation, that process would be biased towards matter, leaving the matter-filled world we see today.
If that happened, Vachaspati showed that there should be a sign of it today: twisted magnetic fields permeating the universe – a fossil of the magnetic monopoles that briefly dominated. And he showed they should look like left-handed screws rather than right-handed screws.
So Vachaspati and his colleagues went looking for them in data from NASA’s Fermi Gamma ray Space Telescope. As gamma rays shoot through the cosmos, they should be bent by any magnetic field they pass through, so if there are helical magnetic fields permeating the universe, that should leave a visible mark on those gamma rays.
All of a twist
Lo and behold, that’s just what they found – well, maybe. “What we found is consistent with them all being left-handed,” says Vachaspati. “But we can’t be sure.” He says there’s less than a one per cent chance that what they see in the Fermi data happened by chance. “That’s being conservative,” he says.
They also found that the twists in the field are a bit bigger than they predicted. “So there is some mystery there,” says Vachaspati. He says more data from Fermi, which is expected this year, will help narrow down the odds.
Nicole Bell from the University of Melbourne in Australia warns that magnetic fields could have been caused in other ways, including from inflation. What’s more, for CP-violation to provide enough matter in the universe you usually need “new physics” – stuff beyond the standard model of particle physics – which hasn’t been confirmed experimentally yet. “But it is a very interesting idea,” she says.
Journal reference: Monthly Notices of the Royal Astronomical Society, DOI: 10.1093/mnras/stv308
Michael Slezak – www.newscientist.com