Yesterday my son and I were driving through Pennsylvania when we stopped for gas. As I drained my wallet filling the tank, he went to the Quickie Mart and returned with $10 worth of 'poppers'. A popper, for those who don't know, is small paper-wrapped wad of explosive. Throw one down on a hard surface and it cracks with the report of a .22, leaving only a few paper shreds behind. Within about two minutes my son had gone through the entire box. Poppers don't last long in the hands of a teenage boy and that makes them a good analogy for antimatter — the universe's strange and elusive "twin" version of mass.
For decades physicists have been trying to trap enough antimatter to perform detailed experiments on its properties. But, like my son's poppers, the antimatter always disappeared quickly, annihilating itself on first contact with any speck of "real" matter in a burst of energy.
Those elusive, antimatter hunting days appear to be over. Yesterday, a team of researchers at CERN managed to trap a significant chunk of antimatter for a full quarter-hour. That's a world record and it means an era of regular antimatter experiments may be just ahead of us.
Antimatter came as a surprise to physicists when it was discovered 80 years ago. Back then scientists had only just started getting used to the idea that all matter was made up of a zoo of particles like the electrically charged electrons (negative charge) and protons (positive charge). Then in 1928 Paul Dirac predicted that electrons must have an oppositely charged "antimatter" twin.
Dirac saw that when an electron meets an oppositely charged antielectron (called a positron) they would annihilate each other in a flash of energy (light). The positron's existence was verified in experiments just a few years later and scientists soon came to realize that every matter particle had an antimatter version as well. An entire periodic chart of antielements should, in principle, be possible, starting with simple antiatoms like antihydrogen (a positron orbiting an antiproton). But they quickly ran headlong into a dilemma.
Where is all the universe's antimatter?
For cosmologists studying the origin of the universe it was pretty clear that equal amounts of matter and antimatter must have spewed out from the fireball at the beginning of creation. But the universe we live in, thankfully, is not made of equal parts matter and antimatter (if it was, every move we made would lead to terrible explosions). There must be some subtle difference between matter and antimatter that blew away the "anti-stuff" early in cosmic history, leaving only our matter-dominated Universe.
In our current epoch antimatter makes only fleeting appearances in man-made particle accelerators or in very high-energy natural events.
The problem for physicists is they have never been able to collect large enough quantities of antimatter to study its properties in detail. Antielements such as antihydrogen just disappear too quickly through collisions with matter. What they needed was a means of producing stable blobs of antimatter to poke, probe and prod in experiments that would allow us to understand its properties on the deepest level.
Now, it appears, they have found the means.
Last year scientists at CERN, the main European particle physics laboratory (also the home of the LHC), were able to form antihydrogen and keep it around for a whopping two-tenths of a second. That was a world record. They achieved their milestone by finding novel ways to keep the antihydrogen from hitting the walls of the container and annihilating itself.
Now the same team (called the ALPHA antimatter experiment) has extended their antimatter trapping out to 16 minutes and 40 seconds. That is a 5,000-fold increase in confinement time. After decades of getting nothing more than a fleeting glimpse of the stuff, keeping a treasure trove of antihydrogen captive for that long is both very impressive and very important.
The strange existence of antimatter and its radical imbalance as a cosmic constituent is a fundamental mystery that has persisted for eight decades. With the ALPHA team's achievement, we may finally be poised to understand not only the universe that is but also the universe that might have been.