Running Out of Matter with Michelle Thaller

July 21, 2026

AI Summary

5 min read

In September 2015, two detectors in Louisiana and Oregon registered the same pattern at the speed of light—a "boom" in the data that turned out to be two black holes, each about thirty times the mass of the Sun, spiraling together and merging 1.4 billion light-years away. In the final two-tenths of a second before they merged, they accelerated from 30% to 60% the speed of light and converted about two solar masses into pure energy. That moment, captured by the Laser Interferometer Gravitational-Wave Observatory (LIGO), remains one of the most energetic events ever measured. For astrophysicist Michelle Thaller, who was a postdoc at Caltech when LIGO was being built, the detection was a vindication of something she once doubted would ever work.

The photon’s strange journey

A listener asked whether a photon that is absorbed and re-emitted or reflected is the same photon or an entirely new one. Thaller and Tyson agreed that the answer is not straightforward. Photons traveling at the speed of light do not experience time or distance—from a photon’s perspective, the universe is a point and no expansion has ever happened. Yet the same photon gets red-shifted as the universe expands, meaning its energy changes, which implies something about its identity has changed too.

Continue reading the full summary in the app — free to try.

Read Full Summary →

Free • No credit card required

Listen to Audio Summary Open in App

Never miss an episode of StarTalk Radio

Get every new episode summarized in your inbox — free, ~5 minutes to read.

No spam. Unsubscribe anytime.

What you'll learn

1 (02:28) **Welcome & Guest Introduction** - Neil introduces Michelle Thaller, fellow astrophysicist and science communicator, recently retired from NASA Goddard Space Flight Center.
2 (06:54) **Warning Sign: Consequences of NASA Budget Cuts** - Michelle describes the impact of recent budget cuts on NASA’s science workforce.
3 (10:42) **Diagnosis: NASA’s Tiny Budget** - Science missions run on under $6 billion/year out of NASA’s ~$30 billion total budget.
4 (17:48) **Cosmic Query #1: Photon Identity Crisis** - Ross asks if a photon absorbed and re-emitted or reflected becomes a new photon with a new quantum history.
5 (22:31) **Mechanism: How Light Slows in a Medium** - Discussion of why light appears slower in air, water, or glass.
6 (26:56) **Cosmic Query #2: Running Out of Matter** - Costa asks if the universe will eventually run out of matter to create new stars, and how we’d notice.
7 (30:46) **Recovery/Application: Greenhouse Effect Connection** - Chuck links the energy degradation process to planetary warming.

+ Full timestamped outline available in the app

Guests on this episode

Michelle Thaller

Show Notes

Could spacetime curve in the opposite direction and produce a repulsive field instead of gravity? Neil deGrasse Tyson and comic co-host Chuck Nice tackle fan questions about photons, heat death, gravitational waves, neutron stars and more with astrophysicist Michelle Thaller.

NOTE: StarTalk+ Patrons can listen to this entire episode commercial-free.

Thanks to our Patrons Richard Asante, Zan Barrage, Nekoda, Charles O'Neal, Fred FredericM, Douglas Torrance, Barbara Ziola, Nightangelj91, Leslie Woodward, Bryan Jones, Lori Tchen, Walter Lockhart, Paul Walker, Brian Kemp, ismael valdés, Pasquale Perrotta, Xavier LaVigne, nova 🧚🏼‍♀️, Everett Corniel, Ron Herman, Ox, Emile Rougeau, Tony Scaringi, Ceedubya, Michael Bohonek, RS, Jeong Lee, YourCousinRicky, Jesse Wassner, Brett, Agustin Cabanas, James Pack, Dave Baxter, Clarence wirley, Sketchy McDoodles, Chris W, clayton clarkson, David Furth, charles price, Robbie Wells, Gilbert Garcia, Pitbull6098, Ashtyn2022, Kate eftink, Charles Sterner, Liz Dub, Rin Dragon, Liviu N. Spiroiu, Elle Belle, John DiNonno, Researcher Siks, Socal, James Adamson, B Mikhail, Dom Tedeschi, Estella Linthicum, Zionic God, Aye Koe, and Robert Galan for supporting us this week.

Subscribe to SiriusXM Podcasts+ to listen to new episodes of StarTalk Radio ad-free and a whole week early.
Start a free trial now on Apple Podcasts or by visiting siriusxm.com/podcastsplus.

Hosted by Simplecast, an AdsWizz company. See pcm.adswizz.com for information about our collection and use of personal data for advertising.