Artist’s impression of matter-antimatter collisions. Pete Linforth
The concept of antimatter has delighted sci-fi fans for years, but it also poses a real question for physicists. Mathematically speaking, it makes sense that for every type of particle in our universe there exists a corresponding antiparticle which is the same but with the opposite charge — so to correspond with the electron, for example, there should be an antielectron, also known as a positron. When antimatter and matter come into contact, they both destroy each other in a flash of energy.
When the Big Bang happened, it should have created equal amounts of both matter and antimatter. And yet matter is everywhere and there is hardly any antimatter in our universe today. Why is that?
A new experiment from CERN, the European Organization for Nuclear Research, has been tackling the question by looking at how matter and antimatter could react differently to Earth’s gravitational field. Physicists think that antimatter could fall at a different rate than matter, which would help to explain why it is less prevalent. But in order to test this, they need to create antimatter particles such as positronium atoms. These are pairs of one electron and one positron, but they only live for a fraction of a second — 142 nanoseconds to be exact — so there isn’t enough time to perform experiments on them.
CERN’s breakthrough is in creating positronium atoms which last much longer — 1140 nanoseconds each. They have also been able to track the velocity of the created positronium atoms, observing that they move at between 70 and 120 kilometers per second, which makes experimenting on them easier. They achieved this using the delightful-sounding “positron-to-positronium converter” which sends out a flash of ultraviolet laser to give positrons more energy so that they live longer.
Eventually scientists can use these longer-lived positronium atoms in experiments to see how they react to gravity, but first they need to check whether the atoms they create are electrically neutral. Fortunately, this can be done without the use of the CERN accelerator which is currently shut down for a two year upgrade program. Most experiments at CERN require the use of the accelerator to create a beam of protons, but this positronium experiment can go ahead even during the shutdown period.
The findings are published in the journal Physical Review A.
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