Antimatter mysteries: Can we make an anti-world?

Making anti-atoms is incredibly time-consuming; making complex ones could take a billion years (Image: NASA)
Making anti-atoms is incredibly time-consuming; making complex ones could take a billion years (Image: NASA)

At the moment physicists are having enough difficulty just taming antihydrogen, the simplest possible anti-atom. Can we ever expect them to make antihelium, and then organic antimolecules made from anticarbon and a whole anti-periodic table, too?

The problem here is that every anti-atom has to be built one subatomic antiparticle at a time. For example, if you want to make antideuterium - like antihydrogen, but with an added antineutron - you first have to make the antineutron. Antineutrons are neutral, making them impossible to steer in the conventional way with electromagnetic fields, so you just have to make great numbers of them and hope that for every million or so antineutrons you make, one ends up in the right place to make an antideuterium atom. "And for every further antineutron or antiproton you add, you lose another factor of a million," says Michael Doser, spokesman for CERN's AEGIS experiment studying the properties of antimatter.
While no one's cracked that problem yet, one experiment at CERN is making use of a neat short cut to at least make something other than antihydrogen. ASACUSA has created atoms of "antiprotonic helium", in which one of the electrons orbiting a helium nucleus is replaced by an antiproton. By studying the light spectra emitted by this composite matter-antimatter atom, the electrical and magnetic properties of the antiproton can be measured with great precision - and compared with those of a regular proton.
As for our chances of making anything more complex, Frank Close, a particle physicist at the University of Oxford, is pessimistic, saying it will take a billion years, give or take. "It depends on how long the human race lasts," he says. It seems that our best bet for spying more exotic elements of the anti-periodic table is to look up at the sky - and hope that somewhere antistars are busy churning them out for us.

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