CERN experiments investigate whether antimatter falls up or down
Physicists at CERN have discovered that antimatter falls down. Sure, it sounds like an obvious thing, but scientists haven’t yet been able to confirm that it responds to gravity in exactly the same way as regular matter does. A new experiment provides the best answer so far.
Antimatter is much like the matter that makes up everything around us, with one important difference: its particles have the opposite electric charge. And that simple difference has some major implications – whenever a particle and its antiparticle meet, they annihilate each other.
Thankfully for us matter-based beings, antimatter is extremely rare in the universe, but nobody really knows why. The Big Bang should have produced equal amounts of matter and antimatter, which would have ended up annihilating the entire contents of the universe billions of years ago. The fact that we’re here today to ask the question shows that some unknown factor created an imbalance.
So physicists are studying antimatter closely to see if there are any other differences between it and regular matter, besides charge, which could account for the imbalance. The Standard Model says that there shouldn’t be any other difference, so if scientists find something, it could open a whole new world of physics.
That means going right back to basics to examine antimatter. For instance, every element absorbs and emits different wavelengths of light, producing a unique fingerprint called an emission spectrum. Antimatter should have the same spectrum as its matter counterpart, but it wasn’t until 2016 that CERN scientists finally checked. Sure enough, antihydrogen was found to have the same spectrum as hydrogen.
How antimatter reacts to gravity is another seemingly simple question that’s taken years of study. It may sound like something we should know already, but most of the time antimatter is suspended in electromagnetic traps to keep it from annihilating with containers. It’s expected that antimatter should respond to gravity the same way as regular matter – but there is a tiny chance that it doesn’t, and may actually fall upwards instead.
To test the idea, the team placed antiprotons and negatively charged hydrogen ions into an electromagnetic device called a Penning trap. Once inside, the particles follow a cyclical trajectory, and by measuring their frequency scientists can calculate their charge-to-mass ratio. This ratio should hold the same for both the matter and antimatter particles, but any difference would be attributed to variations in their interactions with gravity.
And sure enough, the team found that matter and antimatter respond to gravity the same way. At least, within the uncertainty of the experiment, which is within 97 percent of the gravitational acceleration the particles experienced. That’s four times more precise than previous experiments, the team says.
However, that does still leave room for new physics to sneak in. Other experiments are testing antimatter’s interactions with gravity through what sounds like a far more simple approach – dropping antimatter particles and seeing where they go. If these teams find different results to the current experiment, it could hint at physics beyond the Standard Model.
The research was published in the journal Nature.