An international research team has successfully conducted ultra-precise X-ray spectroscopic measurements of helium-like uranium. The team, which includes researchers from Friedrich Schiller University Jena and the Helmholtz Institute Jena (both in Germany), has achieved results demonstrating their success in disentangling and separately testing one-electron two-loop and two-electron quantum electrodynamic effects for extremely strong Coulomb fields of the heaviest nuclei for the first time.