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Lasers produce slow, cold antiatoms

2 min read

So where has all the antimatter gone?

A new way to make colder atoms of antimatter has been found. It could help bring scientists closer to understanding why we, and everything else, are made out of matter instead of antimatter.

According to the best theories, ordinary matter and its shadowy twin were created in approximately equal amounts when the universe came into existence some 14 billion years ago. If that’s true, then where has all the antimatter gone?

“The imbalance is an embarrassing thing in physics, something we don’t talk about,” admits Gerald Gabrielse, Leverett Professor of Physics at Harvard University. To solve this universal mystery, researchers want to get a good look at antimatter atoms. To get such a view, they need a good way to slow them down.

To start with, this stuff is extremely difficult to make. Antimatter moves much faster than a speeding bullet and it annihilates itself when it hits ordinary matter, like air or the walls of a container. The problems involved in overcoming this were solved in 2002 by using supercold vacuum traps that keep antimatter suspended away from the walls with magnetic fields. Using such “traps,” as they are called, antiprotons can be combined with antielectrons to make atoms of antihydrogen.

The process is vastly more difficult than electrons and protons coming together naturally to make plain hydrogen. And added to all the expense and exotic engineering is the fact that such custom-made antiatoms move too fast to get a good look at them.

One way to slow them down is to collide the heavier antiprotons with lighter antielectrons. Gabrielse compares this to “slowing a car by driving it through a garage full of Ping-Pong balls.” Two groups have successfully done such experiments, but the antihydrogen atoms they make still move too fast to see if they are fundamentally different from ordinary hydrogen.

In the antimatter business, slow means cold. The colder the atom, the less energy it has and the slower it moves. These experiments are conducted at temperatures hovering around 455 degrees below zero Fahrenheit.

“We need really cold atoms before we can grab onto them tightly enough to keep them from getting away,” Gabrielse explains. “So far this is as close as we’ve come.”