The episode features Adam Riess, Bloomberg Distinguished Professor at Johns Hopkins University and 2011 Nobel laureate in physics, alongside host Neil deGrasse Tyson and comedian Paul Mercurio at the Hayden Planetarium.

Riess shared the Nobel Prize with Brian Schmidt and Saul Perlmutter for discovering the accelerating expansion of the universe through observations of distant Type 1a supernovae in the late 1990s.

The conversation explores the cutting edge of cosmology, focusing on the Hubble tension - a persistent disagreement between measurements of the universe's expansion rate from the early universe versus local observations.

Discussion covers the cosmic distance ladder, standard candles in astronomy, the nature of Dark Energy, and whether this tension signals new physics or reveals gaps in our understanding of cosmology's standard model.

The Nobel Prize Discovery: Accelerating Universe

Riess won the 2011 Nobel Prize with Brian Schmidt and Saul Perlmutter specifically for discovering the accelerating expansion of the universe, not for explaining what Dark Energy is.

Einstein's cosmological constant was originally introduced to balance gravity and keep the universe static, then abandoned when Hubble showed the universe was expanding, but remained mathematically legitimate.

"Once something is possible in physics, it is always there unless you have evidence that it doesn't exist" - Tyson

In the 1920s, astronomers thought the universe was just the Milky Way galaxy

The Nobel Prize medal itself is 18-carat gold, heavy enough that TSA agents questioned Brian Schmidt when it appeared as a hole in x-ray scans of his backpack.

Type 1a Supernovae as Standard Candles

Type 1a supernovae occur when a white dwarf star reaches the Chandrasekhar limit through mass transfer from a companion star, triggering a thermonuclear explosion at approximately the same mass every time.

These explosions reach billions of times the luminosity of the sun

They're visible halfway across the universe

Only one occurs per galaxy like ours per century

The key advantage over other supernovae is reliability - they always explode at just about the same mass, making them true standard candles unlike core-collapse supernovae which vary widely.

"We would propose for time and say, oh, we'll tell you exactly where the supernova is on Tuesday so you could start observing it Thursday" - Riess describing the revolutionary ability to find supernovae on demand in the 1990s.

Dust contamination was solved by measuring reddening - dust makes objects dimmer and redder, similar to sunsets, allowing correction by measuring how much redder a supernova appears compared to dust-free examples.

The Cosmic Distance Ladder and Measurement Techniques

Parallax uses Earth's orbital diameter as a baseline to measure nearby star distances geometrically, with the Gaia telescope providing exquisite measurements beyond Earth-based capabilities.

Cepheid variable stars, about 100,000 times the luminosity of the sun, served as the second rung but couldn't reach cosmological distances where the universe's expansion history becomes measurable.

Type 1a supernovae provided the breakthrough - billions of times more luminous than the sun, allowing measurements billions of light years back when the universe was younger and expanding differently.

Wide-field cameras on large telescopes in the 1990s enabled simultaneous observation of 100,000 galaxies, making it possible to find supernovae on demand rather than waiting for chance discoveries.

The Hubble Tension: 73 vs 67

The Hubble tension emerged about 10 years ago as a 9% disagreement between local measurements (70-75 km/s/Mpc) and early universe predictions (66-67 km/s/Mpc) from cosmic microwave background observations.

"When people were measuring 50 or 100, they were measuring the same thing. The big difference here is we are measuring opposite ends of the universe and using our story of the universe to connect them" - Riess explaining why this disagreement is profound.

James Webb Space Telescope provides 10 times higher signal-to-noise ratio than Hubble but confirms the same answer, strengthening confidence the tension is real rather than measurement error.

Recent independent teams using JWST and the tip of the red giant branch method measured 74 and 75, further validating local measurements cluster around 73 while early universe predictions remain at 66-67.

"We can rule out a measurement error as a cause of the Hubble tension with very high confidence" - Riess after 10 years of scrutiny with all data publicly archived and cross-checked by independent teams.

Lambda CDM Model and Dark Energy

The Lambda CDM model represents the standard model of cosmology, with Lambda referring to Dark Energy (Einstein's cosmological constant) and CDM meaning cold dark matter.

96% of the universe consists of dark matter and Dark Energy combined

The model successfully describes the universe's inventory but most components remain fundamentally unknown

Dark Energy may be a general phenomenon occurring throughout cosmic history - invoked during inflation shortly after the Big Bang and observed accelerating expansion today.

The Higgs field demonstrates that invisible energy fields in space are regular features of physics, and in Einstein's theory of gravity, such fields automatically produce a push on the universe.

"We are sort of watching the universe to see if there are episodes of Dark Energy" - Riess suggesting there may be multiple episodes beyond inflation and current acceleration.

Possible Explanations and Future Observations

Early Dark Energy theory posits a third episode of Dark Energy between inflation and current acceleration, potentially reconciling the Hubble tension by affecting how we connect early and late universe measurements.

Modifications to early universe physics could include new particles, magnetic fields in the plasma soup, or subtle changes in how energy was distributed before cosmic microwave background radiation escaped.

Thomas Burkert's theory suggests calculations through chunky space using general relativity won't match calculations through smoothly distributed matter, though numerical simulations by others don't replicate his analytical results.

The Nancy Grace Roman Space Telescope launches next year specifically designed to study Dark Energy.

The Vera Rubin Observatory will cover most of the sky every three to four days from the ground, already discovering thousands of asteroids and expected to find a million supernovae.

New facilities including Simons Observatory for CMB measurements, continued LIGO observations, and new Gaia results provide multiple independent approaches to resolving the tension.

Historical Context and Scientific Process

In graduate school during the 1990s, astronomers debated whether the Hubble constant was 50 or 100 - uncertain about the size of the universe by a factor of two, making current 9% disagreement seem precise by comparison.

"Back in the day, half the battle was people had their secret photographic plates in their drawer" - Tyson contrasting past secrecy with modern public data archives enabling democratic cross-checking.

The discovery of Dark Energy solved the age crisis where stars appeared older than the universe - accounting for acceleration pushed the universe's age from young estimates to 13-15 billion years.

Historical parallels to Copernicus show how fundamental ideas (sun-centered universe) can be correct while requiring adjustments (elliptical orbits) - the Big Bang likely remains secure while details need refinement.

"Cosmology used to be considered closer to philosophy than physics" with only two and a half facts, but now has extensive data making it a rigorous laboratory for testing fundamental physics.

Classical physics appeared complete 130 years ago with just a few clouds on the horizon like Mercury's precession, but those cracks led to quantum mechanics and relativity - current tensions may herald similar revolution.