Throw a baseball up and gravity brings it back. For decades astrophysicists assumed the whole universe behaved that way, slowly decelerating after the Big Bang. Then Saul Perlmutter and his rivals discovered the cosmic baseball is actually accelerating away, driven by an invisible repulsive force, and forced a complete rewrite of cosmology.

This deep dive traces how a scientist who set out to find a single hypothetical hidden star ended up measuring the expansion of the entire universe and winning a Nobel Prize. It is a master class in the unintended consequences of rigorous science, from automated 1980s telescopes to dark energy to validating global warming.

• How his failed PhD hunt for the star Nemesis built the image-subtraction pipeline that later detected distant supernovae
• Why Type Ia supernovae make perfect standard candles thanks to the 1.44 solar mass Chandrasekhar limit
• The paradox of supernovae 25 percent dimmer than expected, implying acceleration and reviving Einstein’s cosmological constant
• How a fierce rivalry with the High-Z team led both groups to announce dark energy within weeks in 1998
• How he applied astrophysical noise-filtering methods to the Berkeley Earth project to validate global warming data