Greene explains how Einstein overturned Newton's concept of absolute time, demonstrating that relative motion and gravitational fields cause time to elapse at different rates. He describes how a traveler moving near the speed of light could age one year while thousands of years pass on Earth, a phenomenon confirmed by particle accelerator experiments.
Greene discusses the theoretical possibility of wormholes as tunnels through both space and time, though he expresses skepticism about their practical viability due to energy feedback problems. He addresses string theory, the search for a unified equation describing all fundamental forces, and the idea of parallel universes arising from both quantum mechanics and inflationary cosmology. Greene also shares his view that consciousness is purely physical computation, while acknowledging that science cannot disprove the existence of a divine creator.
Key Moments
Caller defends Edgar Mitchell's epiphany: An emotional caller pushes back on Art over an earlier interview with Apollo 14 astronaut Edgar Mitchell, defending Mitchell's cosmic-consciousness experience as a real spiritual emergency that listeners need to hear about.
Newton was wrong: there is no absolute time: Greene tells Art that Einstein overturned Newton's notion of a single universal clock, and that two observers who simply move relative to each other can genuinely disagree on how much time has elapsed between the same two events.
Spaceship time travel: come back to a dead Earth: Greene walks Art through the standard relativistic thought experiment: travel near light speed for what feels like one year and you can return to find 10,000, 100,000 or a million years have passed on Earth.
Forward time travel real, backward 'an impossibility': Greene tells Art that physics already allows leapfrogging into the future, but that most physicists believe time travel to the past is essentially impossible, and that getting back is the hard part.
Wormholes and the feedback problem: Greene explains how moving one mouth of a wormhole turns it into a tunnel through time, then warns that energy cycling through such a wormhole would build up like audio feedback and destroy it before anyone could pass through.