Why This Universe? 93 - The Moment Dark Energy Appeared (Ft. Adam Riess)
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Sep 15, 2025 
Adam Riess, a Nobel Prize-winning astronomer and professor at Johns Hopkins University, shares the thrilling moments of his pivotal discovery about dark energy. He delves into how dark energy fuels the rapid expansion of our universe, revealing the intense competition between research teams in the 90s to measure cosmic expansion. Riess discusses the challenges of reconciling observational data with theoretical physics and reflects on the initial skepticism that surrounded the announcement of dark energy, reshaping our understanding of the cosmos.
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Missing Mass Tension In The 1990s
- In the early 1990s observers measured only ~20–30% of the critical mass density of the universe.
- This tension challenged inflationary expectations that predicted a critical density of matter.
How Distant Supernovae Were Found
- Riess describes how teams used wide-field imaging, image subtraction, and follow-up spectra to find distant Type Ia supernovae.
- The process required new software, coordinated telescopes, and rapid identification to measure redshifts and distances.
Acceleration Revealed By Fitting Mistake
- Initial fits to the supernova data returned impossible values until acceleration was allowed in the model.
- Once acceleration was included, the data demanded an extra repulsive component beyond matter.