StarTalk Radio: "Past, Present, Future: Time Travel with Brian Greene" Summary

Podcast Information:

• Title: StarTalk Radio
• Host: Neil deGrasse Tyson
• Guest: Brian Greene, Theoretical Physicist and Mathematician
• Episode Title: Past, Present, Future: Time Travel with Brian Greene
• Release Date: December 24, 2024

Introduction to Time Travel

In this episode of StarTalk Radio, astrophysicist Neil deGrasse Tyson delves into the intriguing concept of time travel alongside his guest, renowned theoretical physicist Brian Greene. The conversation is set against the backdrop of Charles Dickens' classic novel A Christmas Carol, which is often cited as one of the earliest literary explorations of time travel.

Neil deGrasse Tyson [02:40]:
"Welcome to StarTalk, your place in the universe where science and pop culture collide."

Chuck Nice [03:06]:
"Always a pleasure to be here. Although I'm not actually, I'm not actually here. I'm coming to you from the future."

This humorous opening by co-host Chuck Nice sets a lighthearted tone for the deep scientific discussions that follow.

Einstein's Relativity and Its Implications for Time Travel

Neil and Brian begin by exploring how Einstein's theories of relativity revolutionized our understanding of time.

Brian Greene [07:04]:
"Time is much more individualistic than anybody would have ever thought. The common view of time was it's universal... Einstein shattered that by showing that time elapses at different rates depending on how you move and your gravitational experience."

They discuss how special relativity introduced the idea that faster movement results in slower ticking clocks relative to a stationary observer. General relativity further expanded this by demonstrating that gravity affects the passage of time, leading to phenomena like time dilation experienced by satellites.

Brian Greene [07:54]:
"The clock on Earth truly is ticking off time at a slower rate than the clock that's floating up there in space."

This discussion highlights real-world applications, such as the need to adjust satellite clocks to account for both their high velocity and their distance from Earth's gravitational pull, ensuring the accuracy of our communication networks.

Experimental Evidence of Time Dilation

Neil brings up historical experiments that validate Einstein's predictions.

Brian Greene [11:24]:
"When they tested these ideas on a Pan Am jet in the 1970s... the net change is not what you would have anticipated. But when you take all the effects into account, motion and gravity that Einstein delineated, the prediction agrees with the observations. Spot on."

He references experiments where atomic clocks on fast-moving jets showed measurable differences compared to those left on the ground, confirming the theory that both velocity and gravity influence the passage of time.

Philosophical Implications and Paradoxes of Time Travel

The conversation shifts to the philosophical dilemmas posed by time travel, particularly the possibility of altering past events.

Chuck Nice [15:45]:
"Suicide via time travel. So those constrictions, since I'm coming from a place that is already set..."

Brian Greene [17:42]:
"If you travel back to an earlier moment in time before your own birth, then you were always part of that moment. Therefore, the causal chain of events that resulted in your own birth remains unchanged."

Brian discusses the concept of chronology protection, a conjecture by Stephen Hawking, which suggests that the laws of physics prevent time travel from creating paradoxes, such as altering one's own existence.

Neil deGrasse Tyson [23:45]:
"But, Brian, it takes away free will."

Brian Greene [23:48]:
"This is a version of negating free will. But I am one of those people who doesn't believe in any variety of free will of the traditional sort."

This segment delves into the deterministic nature of time travel within certain theoretical frameworks, questioning the extent of human free will.

Time Travel in Popular Media

Neil and Brian analyze how time travel is portrayed in films, assessing their scientific accuracy.

Brian Greene [31:07]:
"Interstellar is probably the best one where you have Matthew McConaughey going near a black hole. Time slows down... those are accurate features of Einstein's general theory of relativity."

They commend Interstellar for its faithful representation of time dilation near black holes, a concept grounded in general relativity. Conversely, they critique other portrayals for lacking scientific precision.

Neil deGrasse Tyson [32:11]:
"Kip Thorne helped pioneer LIGO and received the Nobel Prize, and he was the co-recipient of it a few years ago. And Henry did the movie."

This highlights the collaboration between physicists and filmmakers to enhance the scientific authenticity of cinematic narratives.

Advanced Concepts: Tachyons and Wormholes

The discussion moves to more speculative aspects of time travel, including hypothetical particles and spacetime structures.

Chuck Nice [49:03]:
"Is there any idea on how to try and detect the theorized tachyon particle?"

Brian Greene [50:20]:
"A tachyon is a particle that can go faster than the speed of light. If a particle can go faster than light, there are observers who will see it reach its target before it was emitted by the source."

They explore the concept of tachyons—hypothetical particles that move faster than light—and the implications such particles would have on our understanding of causality and the directionality of time.

Brian Greene [37:00]:
"The richness of wormholes really arises when you have a time difference between the two openings. It's fun to have a tunnel through space, but it is mind-blowing to have a tunnel through time."

Wormholes, theoretical passages through spacetime, are discussed as potential mechanisms for time travel, allowing movement between different points in both space and time.

Black Holes and the Information Paradox

The conversation touches upon the black hole information paradox, a pivotal topic in modern physics.

Chuck Nice [45:03]:
"So when you go into a black hole, I'm a chair. I go into a black hole, I get broken down into just particles, okay? That's all because the gravity's so strong now, just the string of particles. I come out during the evaporation. Would I be able to be a chair again?"

Brian Greene [46:24]:
"Stephen Hawking told us that particles will come out and they do carry the imprint of the fact that they were once a chair. And if you measure the particles appropriately, you could reconstruct the chair when those particles come out."

They discuss how, contrary to Hawking's initial assertions that information is lost in black holes, advances in string theory and quantum mechanics suggest that information is preserved, albeit in a highly scrambled form.

Cosmic Queries and Audience Engagement

Throughout the episode, Neil and Brian address questions from listeners, further unpacking the complexities of time travel.

Listener Question [24:26]:
"If controlled backwards time travel was possible today, where do you think your matter or information would travel?"

Brian Greene [37:24]:
"If you can time travel, you also need to space travel. It's really space-time travel. You have to pick the location in time and the location in space."

This emphasizes the intertwined nature of space and time, necessitating precise navigation through both dimensions to achieve controlled time travel.

Listener Question [53:03]:
"If we developed a way to time travel backwards, could we travel to a time before the Big Bang, or would we just break science altogether?"

Brian Greene [53:24]:
"The Big Bang could be the origin of time itself. The notion of 'before' makes sense only when time exists."

They explore the speculative idea of traveling to the very beginning of the universe, concluding that time as we understand it may have originated with the Big Bang, rendering the concept of "before" meaningless within our current framework.

Conclusion and Reflections

As the episode wraps up, Neil and Brian reflect on the profound implications of time travel theories, intertwining scientific principles with philosophical musings.

Neil deGrasse Tyson [57:36]:
"It's been a delight to have you back on StarTalk."

Brian Greene [57:08]:
"Always a pleasure."

Their engaging dialogue not only elucidates complex scientific ideas but also inspires listeners to ponder the nature of time, existence, and the universe.

Neil deGrasse Tyson [57:37]:
"Cosmic queries. I am Neil Degrasse Tyson, your personal astrophysicist. As always, I bid you to keep looking up."

The episode concludes with an invitation to continue exploring the cosmos, encouraging curiosity and scientific inquiry.

Notable Quotes with Timestamps

• Brian Greene [07:04]:
  "Time is much more individualistic than anybody would have ever thought. The common view of time was it's universal... Einstein shattered that by showing that time elapses at different rates depending on how you move and your gravitational experience."

• Brian Greene [11:24]:
  "When they tested these ideas on a Pan Am jet in the 1970s... the net change is not what you would have anticipated. But when you take all the effects into account, motion and gravity that Einstein delineated, the prediction agrees with the observations. Spot on."

• Brian Greene [17:42]:
  "If you travel back to an earlier moment in time before your own birth, then you were always part of that moment. Therefore, the causal chain of events that resulted in your own birth remains unchanged."

• Brian Greene [31:07]:
  "Interstellar is probably the best one where you have Matthew McConaughey going near a black hole. Time slows down... those are accurate features of Einstein's general theory of relativity."

• Brian Greene [50:20]:
  "A tachyon is a particle that can go faster than the speed of light. If a particle can go faster than light, there are observers who will see it reach its target before it was emitted by the source."

• Brian Greene [53:24]:
  "The Big Bang could be the origin of time itself. The notion of 'before' makes sense only when time exists."

Final Thoughts

This episode of StarTalk Radio masterfully blends scientific rigor with accessible explanations, making complex theories about time travel and relativity comprehensible and engaging for a broad audience. Brian Greene's expertise, coupled with Neil's charismatic hosting, offers listeners a comprehensive exploration of one of science's most captivating topics.

Whether you're a seasoned science enthusiast or a curious newcomer, "Past, Present, Future: Time Travel with Brian Greene" provides valuable insights into the fabric of our universe and the tantalizing possibilities that lie within the enigmatic concept of time travel.

Keep looking up and stay curious!