StarTalk Radio – Cosmic Queries: Stoner Edition with Janna Levin
Hosted by Neil deGrasse Tyson
Release Date: February 14, 2025

Overview

In the "Cosmic Queries – Stoner Edition" episode of StarTalk Radio, astrophysicist Neil deGrasse Tyson teams up with co-host Matt Kirschen and renowned physicist Janna Levin to delve into some of the most intriguing questions about black holes, the fabric of space-time, and the very nature of the universe. This episode combines deep scientific insights with a relaxed, conversational tone, making complex topics accessible and engaging for listeners.

1. Gravitational Waves and the Concept of Repulsive Gravity

Timestamp: [04:18]

The episode kicks off with a fascinating question from Matthew Power in New Jersey: “If there were two black holes orbiting one another and generating powerful gravitational waves, is there a possibility that a small object, perhaps a ping pong ball, could actually be carried away by the waves, thus making gravity a repulsive force in this particular case?”

Neil deGrasse Tyson responded enthusiastically, saying, “Wow. This is like a surfing ping pong ball. I love it.” This metaphor sparked a detailed discussion about the nature of gravitational waves and their effects on objects.

Janna Levin elaborated, explaining that while gravitational waves do indeed cause stretching and squeezing in space-time, their effect on small objects like a ping pong ball would be negligible. She clarified, “I don't think it would have enough power to actually carry you along.” However, she also introduced the concept of dark energy, which acts as a repulsive force on cosmic scales, causing the accelerated expansion of the universe.

2. The Universe's Expansion: Into What Are We Expanding?

Timestamp: [09:32]

Matt Kirschen presented another thought-provoking question: “What is the universe expanding into?” This age-old query challenges our understanding of the universe's boundaries and the very concept of "outside" the universe.

Neil deGrasse Tyson humorously remarked, “Everybody wants to know that,” setting the stage for a deeper exploration.

Janna Levin provided clarity by stating, “The universe is the whole space. There’s really no logic to thinking of it expanding into something else.” She emphasized that the universe's expansion doesn't require an external space; instead, space itself is stretching.

Levin further explained, “We are moving with the expansion of the space. We are not moving with respect to our local area.” This analogy likens the universe's expansion to "a surfer riding the wave," helping listeners visualize this abstract concept.

3. Time: A Human Invention or a Fundamental Aspect of the Universe?

Timestamp: [15:17]

One of the more philosophical questions posed by listener Scott Allen was: “Is time just a human invention?” Combining ideas about energy and the perception of time leads to profound discussions about existence and reality.

Janna Levin addressed this by differentiating between time as a dimension and time as a perception. She noted, “If we want to meet, we don’t just specify a point in space. We have to say a moment in time.” This underscores that while our perception of time is influenced by human cognition, time itself operates as a fundamental dimension within the fabric of the universe.

Conversely, Neil deGrasse Tyson referenced a quote by John Archibald Wheeler: “Time is what keeps everything from happening at once.” This highlights the necessity of time in organizing events and processes in the universe.

4. Time Dilation and Its Practical Implications

Timestamp: [23:50]

The discussion shifted to the practical applications of Einstein's theory of relativity, specifically time dilation. Matt Kirschen relayed a question from Jeff Johnson: “Why does gravity or high speed cause an entity to move faster through time?”

Janna Levin clarified that it's actually gravity and high speeds that cause time to slow down relative to an observer in a different frame of reference. She illustrated this with the example of astronauts on the International Space Station (ISS) compared to those on Earth, explaining how both gravitational potential and velocity affect their experience of time.

Neil deGrasse Tyson added, “If we didn’t correct for the time dilation, we would never be able to catch our Uber because it wouldn’t be in the right location.” This underscores the real-world necessity of accounting for time dilation in technologies like GPS, which rely on precise time measurements to function accurately.

5. Black Holes: Temperature, Composition, and Hawking Radiation

Timestamp: [36:01]

A listener from the Czech Republic, Jindric Procupek, asked: “I read that black holes are almost zero Kelvin inside. Why are they so cold and not very hot? Is there a temperature gradient between a black hole center and its event horizon?”

Janna Levin responded by explaining that black holes are cold because they are essentially empty; the dense matter that once formed them has collapsed beyond the event horizon. She emphasized, “Black holes are cold because they're empty.”

She further discussed Hawking radiation, detailing that smaller black holes emit more radiation and are thus hotter, while larger ones emit less and are colder. This emission leads to the eventual evaporation of black holes over incredibly long timescales.

Neil deGrasse Tyson connected this to popular culture, mentioning how the final stages of black hole evaporation would result in explosive bursts of gamma rays, akin to high-energy fireworks in the cosmos.

6. Dark Matter and Black Holes

Timestamp: [43:55]

Gonzalo Castilla from Mexico posed an intriguing question about dark matter: “If dark matter can interact gravitationally with normal matter, it is attracted and eaten by a black hole just like normal matter. What happens with the dark matter as the black hole evaporates? Could there be a dark matter version of Hawking radiation?”

Janna Levin affirmed that Hawking radiation doesn't discriminate between types of matter. She stated, “The black hole will figure out how to radiate all of the information that went into it. That includes dark matter information.” This implies that dark matter would also be emitted through Hawking radiation if it interacts gravitationally.

7. Wormholes and the Possibility of Time Travel

Timestamp: [44:56]

Dylan raised a speculative question about wormholes: “How would we open up a wormhole? Hypothetically speaking, what steps are taken? How much energy would it take?”

Janna Levin addressed the theoretical challenges, explaining that while wormholes can be described mathematically, they require negative energy to remain open—something not observed in nature. She mentioned, “People at KipThorn were writing down wormhole solutions decades ago, and they just looked around and said, well, we don't see any matter like that in the universe.”

Neil deGrasse Tyson humorously referenced the famous "1.21 gigawatts" from Back to the Future, highlighting the immense energy requirements and the current impracticality of creating or sustaining wormholes.

8. Concluding Thoughts and The Stoner Edition Naming

Timestamp: [49:14]

As the episode wrapped up, the hosts playfully debated the appropriateness of labeling this episode the "Stoner Edition." Janna Levin humorously noted, “Anybody who knows me knows if I'm stoned, I'm asleep.” Ultimately, the playful spirit prevailed, acknowledging the relaxed and whimsical nature of the discussions.

Neil deGrasse Tyson concluded with, “This has been StarTalk. Cosmic Queries, black holes, space-time continuum, which we dubbed the Stoner Edition. I'm Neil deGrasse Tyson, your personal astrophysicist. Keep looking up.”

Notable Quotes:

• Matt Kirschen [04:18]: “If there were two black holes orbiting one another and generating powerful gravitational waves, is there a possibility that a small object, perhaps a ping pong ball, could actually be carried away by the waves, thus making gravity a repulsive force in this particular case?”

• Neil deGrasse Tyson [15:17]: “Time is what keeps everything from happening at once.”

• Janna Levin [36:01]: “Black holes are cold because they're empty. There's no dense object left once matter has collapsed beyond the event horizon.”

• Neil deGrasse Tyson [30:57]: “If we didn’t correct for the time dilation, we would never be able to catch our Uber because it wouldn’t be in the right location.”

Final Thoughts

This episode of StarTalk Radio masterfully blends complex astrophysical concepts with relatable analogies and humor. Neil deGrasse Tyson, along with Matt Kirschen and Janna Levin, navigate through listeners' cosmic queries, providing clarity on topics ranging from the enigmatic nature of black holes to the fundamental aspects of time and space. Whether you're a seasoned science enthusiast or a curious newcomer, this "Stoner Edition" offers a captivating journey through the wonders of the universe.

Stay Connected:

• Matt Kirschen on Twitter: @Makirshan
• Janna Levin on Twitter: @JanaLevin
• StarTalk Radio: Subscribe on SiriusXM Podcasts+, Apple Podcasts, and other major platforms for more enlightening discussions.

Keep Looking Up!