When the Big Bang occurred roughly 13.8 billion years ago, equal quantities of matter and antimatter were created — at least that’s what our current theoretical models tell us. The problem is, matter and antimatter particles annihilate each other when they come in contact. This means if our understanding of the universe is correct, it should not exist at all.
Obviously, as is attested by the fact that the universe exists, there is something fundamentally incomplete — if not outright wrong — in our theories that describe reality. Either significantly more matter was created by the Big Bang, or there is an as-of-yet-undiscovered asymmetry between matter particles and their antimatter counterparts.
If this asymmetry — known as Charge, Parity, Time Reversal (CPT) violation in physics jargon — does exist, the only way to detect it would be to create and observe antimatter particles.
For several decades, scientists across the world, including those at the European Organization for Nuclear Research (CERN), have been looking for signs of this asymmetry — so far, unsuccessfully.
In another effort aimed at understanding the difference between matter and antimatter, researchers at CERN announced the installation of a new experiment Friday. Gravitational Behaviour of Antihydrogen at Rest (GBAR), which is designed to study how gravity affects antimatter particles, is the first of the five experiments that will be connected to the Extra Low Energy Antiproton (ELENA) ruing — an instrument that would slow antimatter particles.
“Einstein’s Equivalence Principle states that the trajectory of a particle is independent of its composition and internal structure when it is only submitted to gravitational forces,” Patrice Pérez, GBAR spokesperson, said in a statement. “If we find out that gravity has a different effect on antimatter, this would mean that we still have a lot to learn about the universe.”
The GBAR experiment will use antiprotons and positrons — the antimatter equivalent of protons and electrons, respectively — to create antihydrogen ions, which contain one antiproton and two positrons. The velocity of these ions would then be reduced to roughly half a metre per second (1.6 feet per second).
“Then, trapped by an electric field, one of their positrons will be removed with a laser, which will make them neutral again,” CERN said in the statement. “The only force acting on them at this point will be gravity and they will be free to make a 20-centimetre fall, during which researchers will observe their behaviour.”
Several experiments at CERN are already dedicated to the study of antimatter and its properties. Two other experiments — AEGIS and ALPHA — are also studying the effect of gravity on antimatter.
The installation GBAR comes just months after researchers associated with the ASACUSA, or the Atomic Spectroscopy And Collisions Using Slow Antiprotons, collaboration at CERN reported a new precision measurement of the mass of an antiproton relative to that of an electron.