StarTalk Radio – Gravity’s Cosmic Symphony with Kelly Holley-Bockelmann

Host: Neil deGrasse Tyson
Co-host: Chuck Nice
Guest: Dr. Kelly Holley-Bockelmann (Vanderbilt University physicist, Chair of NASA's LISA Study Team)
Air date: September 16, 2025

Overview

This episode centers on the quest to detect gravitational waves with the next-generation space observatory LISA (Laser Interferometer Space Antenna). Dr. Kelly Holley-Bockelmann joins Neil deGrasse Tyson and Chuck Nice to explore how LISA will expand humanity’s grasp of the universe’s most massive, mysterious objects. The episode dives into the technology, science, and global collaboration behind LISA, as well as the urgent funding and political questions shaping its future.

Key Discussion Points and Insights

1. Introducing Kelly Holley-Bockelmann and the Bridge Program

[04:00–07:35]

• Kelly is a physics professor at Vanderbilt, recent chair of NASA's Astrophysics Advisory Committee, and leads the Fisk-Vanderbilt Bridge Program.
• The Bridge Program increases graduate opportunities for underrepresented students by valuing creativity and community-mindedness as much as standardized metrics:
  • “We need folks that have diversity of thought and background and who are creative to be able to tackle the big problems of today.” (Kelly, 05:48)

2. What Makes LISA Different from LIGO?

[07:34–13:14]

• LIGO detects gravitational waves from stellar-mass black holes with 4-km-long arms on Earth.
• LISA will look for more massive objects with much longer arms (2.5 million km per side in a triangle, stretching as wide as orbits around the Sun).
• The spacecraft are not physically connected but form a triangle by carefully measuring laser travel times between test masses floating in space.
  • “LISA…has arms…so long that they’re bigger than the entire Earth. You need to go into space.” (Kelly, 08:15)
  • “You want to let these test masses…map space time... looking for deviations from the lengths of the triangles. That is because a gravitational wave has passed by.” (Kelly, 09:54)
• Measurement relies on extremely precise lasers, using the speed of light as a reference.

3. The Science Goals: What Does LISA Hope to Detect?

[15:02–20:09]

• LIGO opened the window on gravitational waves from stellar-mass black holes. LISA is tuned for supermassive and massive black holes merging (millions to billions times solar mass).
• Kelly describes the anticipation:
  • “As soon as LISA turns on, you’re going to be able to detect all of the individual black hole stellar-mass binaries and neutron star binaries and white dwarf binaries. There’s supposed to be millions of these in our Milky Way.” (Kelly, 18:28)
• LISA will “hear” a background hum of the gravitational universe and catch rare, enormous mergers.
• “The wonderful thing about LISA is it’s opening this new window to the universe…And the most exciting thing is…there’s going to be something that we don’t know that is in that window. I can’t wait.” (Kelly, 20:40)

4. The Design and Technical Challenges

[21:04–31:10]

• The triangle configuration is optimal for cost and redundancy; three nodes (test masses) floating in space, equipped with lasers.
• “They’re the rubber duckies on the wave itself.” (Chuck, 21:58)
  • Precise cubes made of platinum and gold, not spheres, because cubes can be machined to exacting specs.
• Every source of disturbance, down to single air molecules or solar wind, must be accounted for.
• “The whole name of the game for LISA is to keep everything as still as possible…Individual air molecules hitting that test mass will fake a gravitational wave.” (Kelly, 48:38)

5. Detection Sensitivity, Signal Strengths, and Analogy

[28:31–31:10]

• LISA will not be as sensitive as LIGO in absolute distance but compensates by its huge scale—changes in separation of one part in 10^20.
• Larger astronomical sources produce much "louder" signals; detecting them is like catching a fly ball with an oversized glove.
• “You’re catching a fly ball with one of those novelty gloves.” (Chuck, 30:29)
• “These are really, really loud signals ... your instrument just has to work and then you’ll definitely catch the ... gravitational wave signal.” (Kelly, 30:54)

6. The Politics and Perils of Big Science Funding

[31:10–35:37]

• LISA is an ESA-led (European Space Agency) mission, with NASA as a junior partner.
• U.S. funding instability threatens participation:
  • “The latest president’s budget request has zeroed out LISA... If this request goes through, the US can no longer participate and give our technology to this mission.” (Kelly, 32:40)
• Neil and Chuck discuss the risk of the U.S. losing ground if China or others step in and the historical context of science funding booms and busts.
• “We are losing out. We’re not going to be able to have the technological know-how. We’re not going to have the stable of people who can solve big problems. And so we lose out. And that sucks for us.” (Kelly, 34:05)

7. Spinoffs and Broader Impact

[38:41–40:09]

• Technology for LISA may help future “Solar System Positioning Systems” (like GPS, but for interplanetary travel).
• Precision laser communication and navigation developed for LISA could become essential for Moon, Mars, and beyond.
  • “GPS is not going to be sufficient for where we need to go in the future. And LISA really helps us get there.” (Kelly, 39:59)

8. Systematic Errors, Pulsar Navigation, and the Nature of Scientific Advance

[41:36–43:42]

• Using pulsars for galactic navigation requires knowing our own solar system position with extreme precision—a challenge Lisa-related tech could help solve.
• The episode explores systematic vs. statistical errors and how those can mislead experiments.
• “The entire direction the experiment is going is wrong because of a systematic error.” (Neil, 41:38)
• LISA is structured collaboratively, with various nations (including the U.S. and Europe) responsible for different mission elements. Prior incidents of NASA withdrawing left ESA planning for full independence.

9. Explaining the Magic: What is an Interferometer?

[43:42–47:14]

• Neil prompts Kelly to explain interferometry succinctly:
  • “If the time it takes to go from one side of the arm to another is exactly the same, then the light will interfere with each other…If the arm lengths are a little bit different…you get to see a little bit of light still left over.” (Kelly, 44:19)
• Neil recounts Galileo’s early “lantern” attempts to measure the speed of light, contrasting with LISA’s laser precision.

10. Final Science Nuggets and The Joy of Being Wrong

[51:45–54:07]

• Lisa could detect gravitational waves from primordial black holes if they exist; Kelly is actively researching their signatures.
• She emphasizes the thrill of discovery when nature surprises scientists:
  • “I cannot wait to be wrong. That’s the coolest part.” (Kelly, 52:52)
  • Neil: “They have no idea how delighted we are when stuff breaks.”

Memorable Quotes & Moments

• On the scale of LISA:
  “It is so big that if you were to put it around the Sun… the Sun would fit right in it.” (Kelly, 09:26)
• On being prepared to discover the unexpected:
  “The most exciting thing is…there’s going to be something that we don’t know that is in that window. I can’t wait.” (Kelly, 20:40)
• On scientific joy in the face of surprises:
  “I cannot wait to be wrong. That’s the coolest part.” (Kelly, 52:52)
• On international collaboration and funding uncertainty:
  “We broke up with them once, and ESA said, ‘We’re going to have a contingency plan.’ And so now we could well be breaking up with them again.” (Kelly, 42:54)
• Cosmic perspective (Neil):
  “As we grow our area of knowledge, so too grows the perimeter of our ignorance. So that science indeed is an endless frontier.” (Neil, 55:50)

Timestamps for Important Segments

• [04:00] – Kelly Holley-Bockelmann’s intro & Bridge Program
• [07:34] – LISA basics and key differences from LIGO
• [08:15] – LISA’s colossal scale explained
• [09:54] – How LISA’s free-floating cubes “map spacetime”
• [15:02] – LISA’s science goals: massive black holes, galactic discoveries
• [18:28] – LISA's ability to hear a “din” of gravitational wave sources
• [20:40] – Excitement over opening a new observational window
• [21:58] – Test masses as “rubber duckies” on spacetime waves
• [28:31] – LISA’s detection sensitivity and scale analogy
• [32:40] – The threat of U.S. withdrawal from Lisa funding
• [38:41] – Solar system navigation and spinoff tech
• [44:19] – Kelly explains “interferometer” in plain language
• [52:52] – Joy of being wrong and scientific discovery

Conclusion

This episode offers a lively, wide-ranging window into how the next era of gravitational wave astronomy could reshape our view of the cosmos. It’s a nuanced mix of science, curiosity, engineering, and the human drama of international collaboration and scientific ambition, shot through with the playful, irreverent tone that makes StarTalk a fan favorite.

For those inspired to act, Kelly urges listeners to support the mission via SaveLISA.org and by contacting representatives, highlighting the stakes: “It’s going to be the best thing. It’s gonna make us all wrong, and it’s—” (Kelly, 53:39).

“Once again…we’re on the brink of opening up a new window to the universe…as we grow our area of knowledge, so too grows the perimeter of our ignorance.” — Neil deGrasse Tyson, [55:50]