Lab report

Research into antimatter, the mirror image of ordinary matter, comes closer to telling us why the universe isn’t empty
December 15, 2010
Nobel prize winners Andre Geim (left) and Konstantin Novoselov




Physicists working on a project called Alpha at Cern, the European centre for particle physics near Geneva, recently announced they have made and trapped 38 atoms of antihydrogen, the antimatter counterpart of ordinary hydrogen. Antimatter is the “mirror image” of the ordinary matter that makes up stars, planets and people. The two forms of matter annihilate on contact, converting their mass to energy in a pure expression of the dictum E=mc2. Alpha aims to understand why there is so much more ordinary matter than antimatter. If there weren’t, the two would have annihilated each other perfectly in the early stages of the big bang, and the universe would be empty of matter. So the question is really: why are we here at all? To which the answer surely involves as yet undiscovered physical laws.

But with the media hype came confusion. This is not the first time antihydrogen has been made. And this experiment is distinct from the Large Hadron Collider, a reminder that the world of high-energy physics does not revolve around that accelerator. The latest findings emerge from an instrument called the Antiproton Decelerator. Just as a hydrogen atom is a proton orbited by an electron, antihydrogen consists of an antiproton orbited by an antielectron (called a positron). The decelerator makes antiprotons by colliding atoms into a metal target at high energy, and then cools them using magnetic and electric fields. To make antihydrogen, the antiprotons are mixed with positrons. An earlier project, Athena, made thousands of antihydrogen atoms this way in 2002. But the Alpha antiatoms are trapped in a magnetic field, so they don’t as quickly drift against the walls of the apparatus and annihilate when they hit ordinary atoms. Detained in this way, antiatoms can be studied at leisure. The results so far tell us nothing about why they are outnumbered by regular atoms, but show we are ready to start looking.

HIS DARK MATERIAL

Progress in fundamental physics doesn’t always need Herculean engineering on the scale of Cern. Graphene, the material garlanded in October by the Nobel prize in physics, shows there is still room for bench-top exploration too. Accounts of the prize-winning research by Manchester University’s Andre Geim and Konstantin Novoselov have tended to focus on the practical uses of graphene. It is a candidate fabric for a new, carbon-based microelectronics—whether in computers, cookers or satellites—that is faster, smaller and perhaps cheaper than silicon. Samsung predicts graphene’s first commercial applications are two to three years away, among them touch-sensitive display screens. But it could plumb more recondite theoretical questions too.

It is basically the same substance as plain old graphite, the crystalline form of pure carbon familiar as pencil “lead” and a lubricant. It consists of a single sheet of carbon atoms joined into a honeycomb of hexagons; in graphite, countless such sheets are stacked atop each other. Geim and Novoselov found that the sheets can be separated by using sticky tape to strip away the layers. Although just one atom thick, a graphene sheet is strong and flexible. Graphene is just the latest in a succession of new carbon-based materials. Swap some hexagons for pentagons and the sheets curl into bowl shapes, which can close up on themselves in cage-shaped molecules called fullerenes, the subject of a chemistry Nobel in 1996. Curl the sheets into tiny cylinders and you have carbon nanotubes, the ultimate carbon fibres with potential applications ranging from aerospace engineering to cell biology. What’s more, researchers were already exploring the folding of graphene sheets before Geim and Novoselov worked out how to make them so easily. That’s one reason why there have been grumblings about the Swedish Academy’s award, which seemed to ascribe too much novelty to the pair.

But what distinguished the work of Geim and Novoselov was their focus on the electronic properties of graphene. Graphite itself is a semiconductor, but the currents in graphene are constrained to two dimensions—they have to stay “on the sheet”—and that makes its electronic behaviour weird. The electrons appear to move at the speed of light and as though they have no mass. As a result, graphene electronics is governed by quantum rules, and strips of the material could act as components of a quantum computer, which would be potentially more powerful than current devices. Graphene might also provide a medium for investigating bizarre quantum behaviour. In short, it may be as a playground for fundamental physics, as much as a technological game-changer, that the material will flourish.