Physicists have succeeded for the first time in trapping atoms of anti-matter hydrogen, or antihydrogen. The feat takes researchers one step closer to seeing how antihydrogen might differ from normal hydrogen.
That, in turn, could reveal all sorts of things about gravity and perhaps shed light on what happened to all the antimatter that theoretically should be, but isn't, present in the universe.
Antimatter is the same as regular matter except that each particle has an opposite charge. So whereas an electron has a negative charge, its antimatter counterpart, a positron, has a positive charge and they annihilate each other when they get too close. According to the rules of particle physics, all matter should behave the same, even if you flip the charge (a.k.a. parity) of all particles.
That's the theory, anyway, but no one has been able to test it.
Any differences between antihydrogen and hydrogen, such as differences in the spectra of light they give off or how they experience the Earth's gravity, would overthrow the standard model of particle physics.
It could also be a clue to the mystery of why there is so little antimatter in the universe today.
"This is a big step," said Clifford Surko of the University of California at San Diego. Two groups have been working on trapping antihydrogen at the European Organization for Nuclear Research (CERN) in Geneva, Switzerland, he explained. "The big deal is that one group has succeeded."
Scientists have been able to make lots of antihydrogen atoms since 2002. However, the atoms have only lasted a microsecond before hitting normal matter and vanishing in a flash of gamma rays. The problem is that antihydrogen is a neutral atom, which means it has no strong electrical charge (positive or negative). That means it can't be held safely away from regular matter with the same magnetic "bottles" researchers have designed to keep anti-protons and anti-electrons (better known as positrons) away from regular matter.
And if you can't trap the atoms, they won't last long.
What the researchers on the ALPHA (Antihydrogen Laser PHysics Apparatus) team did was to exploit the tiny magnetic moment of antihydrogen, which makes it act like a very weak, very tiny bar magnet. They did this by using a container flanked by steeply increasing magnetic fields, called magnetic mirrors, that reflect the antihydrogen atoms back to the center of the container.
For this trap to work they had to also cool the antihydrogen to less and a half degree above absolute zero. That was a feat in itself, since the man-made antiprotons used to make antihydrogen are endowed with about 100 billion times more energy than needed to make this trap work.
"The trap that you make for this is very, very weak," explained Joel Fajans, a University of California professor of physics, Lawrence Berkeley National Laboratory scientist and ALPHA team member. The team has published a short report of their accomplishment in the Nov. 18 issue of the journal Nature.
The team know the trap worked because they made about 10 million antihydrogen atoms which promptly obliterated themselves. Then they turned off their new trap and saw 38 more obliterations -- meaning those 38 antihydrogens stuck in the trap.
"We produced 10 million and we trapped 38," Fajans said. That may not seem like a lot, but it's 38 more than have ever been trapped before.
As to what they hope to do with the trapped antihydrogen, the first experiment they are hoping to do is check the light spectrum it gives off when it glows. Theory suggests it should be exactly the same as hydrogen. But what if it isn't?
"You'd be naïve to think that the spectra of antihydrogen would be any different," said Fajans. But science can be surprising, he said. If differences are found, it could undermine some very basic ideas about how the universe works.
There's also the matter of all that missing antimatter all over the universe.
"At some level that's a fundamental mystery," said Fajans.
"There should be as much antimatter as matter," agreed Surko. "What that says is that there is some asymmetry that is making it the way it is. And we don't know what that is."
Finally, there is the matter of gravity. Could antihydrogen also exhibit anti-gravity properties?
"It's incredibly unlikely that it will fall up," said Fajans, "but it might fall at a different rate" which could tell us something about the nature of gravity.