The galaxy cluster MACSJ0717.5+3745, must be made of matter just like we are, or there would be evidence of matter-antimatter annihilation along the line of sight. Image credit: NASA, ESA and the HST Frontier Fields team (STScI).

Why measuring antimatter is the key to our Universe

The laws of physics are symmetric, but the Universe isn’t. Something’s gotta give.

“If antimatter and matter make contact, both are destroyed instantly. Physicists call the process ‘annihilation.” -Dan Brown

When aliens come to our Solar System, hail us and send us their very first message, it likely won’t be, “take us to your leader,” but rather, “are you made of matter or antimatter?” Based on all the observations we’ve ever made, it appears that all the structures we know of in the Universe — planets, stars, gas, galaxies and more — are made of matter and not antimatter. There are signs of matter/antimatter annihilation, but the antimatter we see is less than 0.1% of the matter in all locations. One the one hand, we know our Universe is dominated by matter and not antimatter; we might be so confident in this fact that we’d be willing to shake hands with an alien without even asking the key question.

An artist’s conception of the planetary system Kepler-42. We have every reason to believe it’s all made of matter, and not antimatter. Image credit: NASA/JPL-Caltech.

But on the other hand, every interaction that creates or destroys matter also creates or destroys an equal amount of antimatter. So how do we reconcile these two things? How do we have a…