Holger Motzkau · CC BY-SA 3.0

Shared the 2011 Nobel Prize in Physics with Saul Perlmutter and Brian Schmidt for using distant supernovae to show that the universe's expansion is not slowing down, as had been assumed, but accelerating. An astrophysicist at Johns Hopkins and the Space Telescope Science Institute, he has since become a central figure in the "Hubble tension" debate — a persistent mismatch between the expansion rate measured from nearby supernovae and the rate inferred from the cosmic microwave background.