One of the persistent mysteries about our Universe is the extreme imbalance between matter and antimatter. Antimatter and matter were both generated during the Big Bang, but the Universe is now dominated by ordinary matter, and we don't know why that should be the case. To solve that mystery, an obvious place to look for clues would be in antimatter itself. If researchers could find something different about antimatter’s behavior, it might hint at an explanation for the extreme disparity.
To that end, a team of researchers decided to test whether hydrogen and antihydrogen have the same spectrum—do they absorb and emit light at the same wavelengths. They generated the first-ever laser-spectroscopic measurement of an antimatter atom, but the results look an awful lot like a regular hydrogen atom.
Antimatter is the same as matter but has the opposite electrical charge. So, while an ordinary hydrogen atom is made of a proton (positive charge) and a much smaller electron (negative charge), an anti-hydrogen atom is composed of an anti-proton (negative) and an anti-electron, or “positron” (positive).