StarTalk Radio Episode Summary: "Cosmic Queries – Negative Gravity"

Release Date: May 13, 2025
Host: Neil deGrasse Tyson
Co-Host: Paul Mercurio
Episode Title: Cosmic Queries – Negative Gravity

Introduction

In this engaging episode of StarTalk Radio, astrophysicist Neil deGrasse Tyson teams up with co-host Paul Mercurio to delve into listener-submitted cosmic queries. The duo combines science, pop culture, and humor to address complex astronomical and physical phenomena, making the universe accessible and entertaining for all listeners.

Listener Questions

1. Will Black Holes Outnumber Stars in the Future?

   Listener: Julian from Atlanta ([15:24])

   Discussion Highlights:

   • Black Hole Formation: Paul explains that only a small fraction of stars (approximately one in a thousand) are massive enough to end their lives as black holes.

     Paul Mercurio: “The initial mass function favors low mass stars. And high mass stars are just rare.” ([18:08])

   • Black Hole Evaporation: Referencing Stephen Hawking's theory, Paul notes that black holes evaporate extremely slowly over time, ensuring they won't dominate the cosmos immediately.

     Paul Mercurio: “They will outnumber stars in a trillion years, a few trillion years when the lowest mass stars burn out their fuel.” ([18:06])

   • Long-Term Outlook: While black holes will eventually outnumber stars billions of years in the future, the current universe still boasts a vast population of stars.

2. Is the Speed of Light's Value Arbitrary?

   Listener: Cesar Fradique from Bogota, Colombia ([15:30])

   Discussion Highlights:

   • Fundamental Constant: Paul emphasizes that the speed of light (c) is a fundamental constant in physics, precisely measured and integral to defining units like the meter.

     Paul Mercurio: “You're losing gravity anytime any matter or energy leaves the system.” ([49:21])

   • Arbitrariness of Units: Neil and Paul debate whether the value of c could be different, ultimately agreeing that while units are arbitrary, the speed itself remains a constant.

     Paul Mercurio: “The units are arbitrary, but the speed that we're measuring is not. That is real and it's fundamental.” ([21:03])

3. Would a Different Star Color Affect Our Planet’s Appearance?

   Listener: Captain Carl from St. Thomas, US Virgin Islands ([30:38])

   Discussion Highlights:

   • Color Perception: Paul explains that if Earth orbited a star emitting predominantly blue or red light, the colors perceived on the planet would shift accordingly.

     Paul Mercurio: “You have Roy G. Biv. Do you know Roy G. Biv? Red, orange, yellow, green, blue, indigo, violet.” ([31:23])

   • Evolutionary Adaptations: He suggests that life forms would likely evolve to perceive the prevalent wavelengths, altering our experience of color.

     Paul Mercurio: “If we evolved there, there's no reason why our evolutionary path wouldn't have divided up the blue light into different subcategories.” ([30:49])

4. Can the Cosmic Microwave Background Serve as a Universal Clock?

   Listener: John Mayhoy from Parkland, Florida ([35:30])

   Discussion Highlights:

   • Universality of the CMB: Paul confirms that the cosmic microwave background (CMB) can act as a universal clock, as it represents a uniform snapshot of the early universe, allowing accurate age determination.

     Paul Mercurio: “Yes, because every part of the universe was in the same place at the same time 13.8 billion years ago.” ([35:35])

   • Age Consistency: The age derived from the CMB would be consistent throughout the universe, given its uniform origin.

     Paul Mercurio: “They will outnumber stars in a trillion years, a few trillion years when the lowest mass stars burn out their fuel.” ([36:46])

5. How Does Time Function in Zero Gravity and Motionless Conditions?

   Listener: Joe Liparella from Pennsylvania ([37:11])

   Discussion Highlights:

   • Relativity and Time: Paul discusses Einstein's theory of relativity, explaining that in the absence of gravity, time would pass more quickly for an object.

     Paul Mercurio: “We are losing gravity anytime any matter or energy leaves the system.” ([49:21])

   • Tachyons and Time Travel: They explore the hypothetical particles called tachyons, which travel faster than light and could theoretically move backward in time, though none have been discovered.

     Paul Mercurio: “It's called the initial mass function specifically. And the initial mass function favors low mass stars.” ([37:39])

   • Practical Implications: Neil humorously muses about anti-aging and the complexities of time manipulation.

     Neil deGrasse Tyson: “Why can’t you presume that this life form is smarter and has the ability to see what we've been doing.” ([29:25])

6. Understanding Buoyancy

   Listener: Dennis Alberti from St. Louis ([44:31])

   Discussion Highlights:

   • Basic Principles: Paul breaks down buoyancy as a function of density, explaining that objects less dense than their surrounding medium will float.

     Paul Mercurio: “It's about density and gravity. If you are less dense than the medium you're immersed in, you will float to the top.” ([44:38])

   • Applications: The conversation includes how boat design leverages buoyancy principles, transitioning from historical wooden vessels to modern metal submarines.

     Paul Mercurio: “If you carve it into a volume, the mass of the shell divided by the full volume reduces the density below water, allowing it to float.” ([45:38])

7. Gravity and Energy Loss in Nuclear Reactions

   Listener: Terry Burke from St. Louis ([47:15])

   Discussion Highlights:

   • Mass-Energy Equivalence: Paul explains that in nuclear fission and fusion, losing mass converts it into energy, which still contributes to the system's gravity due to Einstein's equation ( E = mc^2 ).

     Neil deGrasse Tyson: “So the answer is no. Is the gravity associated with the loss?” ([48:10])

   • Gravitational Impact: While mass loss would nominally reduce gravity, the equivalent energy retains gravitational influence, ensuring overall gravitational consistency.

     Paul Mercurio: “Matter and energy are one and the same thing, so they each distort the fabric of space and time.” ([48:28])

8. Supernova Remnants in the Solar System

   Listener: Mark Learned from Portland, Oregon ([50:00])

   Discussion Highlights:

   • Star Formation and Supernovae: Paul discusses how the galaxy’s rotation disperses supernova debris, which then contributes to the formation of new stars enriched with heavy elements.

     Paul Mercurio: “Supernova guts are scattered everywhere, and the galaxy's differential rotation shears the gas clouds, mixing the debris.” ([50:16])

   • Galactic Recycling: This process ensures that elements from past supernovae are incorporated into future generations of stars, fostering a cycle of stellar evolution and material enrichment.

     Paul Mercurio: “Next generation of stars is gonna have all the ingredients from that last round of supernova explosions.” ([50:54])

Conclusion

Throughout "Cosmic Queries – Negative Gravity," Neil deGrasse Tyson and Paul Mercurio adeptly bridge the gap between intricate scientific concepts and everyday understanding. Their insightful discussions not only answer listener questions but also spark curiosity about the universe's vast and mysterious nature. By intertwining humor with expertise, the episode exemplifies StarTalk Radio's mission to make science entertaining and accessible to all.

Notable Quotes with Timestamps

• Black Holes and Stars:

  Paul Mercurio: “The initial mass function favors low mass stars. And high mass stars are just rare.” ([18:08])

• Speed of Light:

  Paul Mercurio: “The units are arbitrary, but the speed that we're measuring is not. That is real and it's fundamental.” ([21:03])

• Relativity and Time:

  Paul Mercurio: “We have stars today that are born out of these pockets of gas that are still alive and thriving, and we've only had one or two black holes, so. No. Black holes do not outnumber stars.” ([18:06])

• Buoyancy:

  Paul Mercurio: “It's easy and simple. If you have less density than the medium, you float.” ([44:38])

• Mass-Energy Equivalence:

  Paul Mercurio: “Matter and energy are one and the same thing, so they each distort the fabric of space and time.” ([48:28])

Final Thoughts

This episode of StarTalk Radio showcases the dynamic interplay between Neil deGrasse Tyson and Paul Mercurio, offering listeners a captivating exploration of cosmic phenomena. Whether contemplating the future balance of stars and black holes or unraveling the nuances of buoyancy, the hosts provide clarity and intrigue, encouraging all to keep looking up.