positronium

From Forbes, Dec. 14, 2020: Fermilab scientist Don Lincoln explains a new measurement performed by scientists at University College London that has the potential to cause researchers to look again at theories of electromagnetism. The team studied the behavior of an exotic atom called “positronium” and found a surprising difference between the prediction and measurement energy level of a specific energy transition. Positronium is an atom that consists solely of an electron and an antimatter electron.