Why This Universe? 94 - Inside the Hubble Tension With Adam Riess
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Sep 29, 2025 
Nobel Prize-winning cosmologist Adam Riess dives into the fascinating world of cosmic expansion and the notorious Hubble Tension. He explains how two measurements of the universe's expansion rate yield wildly different results, exploring the intricacies of measuring the Hubble constant using Type Ia supernovae and Cepheid variables. Riess discusses statistical significance and the implications of potential new physics to resolve these discrepancies. With a mix of precision science and engaging insights, he sheds light on the challenges facing modern cosmology.
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Hubble Constant Needs Distances
- The Hubble constant measures the present expansion rate by combining redshift and distance measurements.
- Measuring redshift is easy, but accurate distances are the hard and crucial part.
Anchor The Ladder With Parallax
- Use geometric parallax as the foundational first rung of the distance ladder whenever possible.
- Calibrate farther steps (Cepheids, supernovae) to parallax to reduce systematic errors.
Cepheids Bridge To Supernovae
- Cepheid variable stars provide a predictable luminosity via their period-luminosity relation.
- Calibrated Cepheids in nearby galaxies let you infer type Ia supernova luminosities and extend distances outward.