115 | Netta Engelhardt on Black Hole Information, Wormholes, and Quantum Gravity
Sep 21, 2020
01:26:59
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Netta Engelhardt discusses the black hole information puzzle, the role of wormholes in understanding it, and its implications for quantum gravity. They explore concepts such as black hole evaporation, entropy, and the second law of thermodynamics. They also discuss entanglement in quantum mechanics, the relationship between conformal field theory and anti-de Sitter space, and the search for an independent description of quantum gravity. They highlight recent progress in understanding the black hole information paradox and the concept of information conservation in black holes. The discussion delves into the gravitational path integral and its ability to reveal insights into information conservation.
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Quick takeaways
Recent progress in understanding the nature of black holes suggests that information may be preserved through subtle effects relating the radiation leaving a black hole to what's going on inside.
The ADS-CFT correspondence provides a duality between quantum gravity and a quantum field theory without gravity, showing that if a conformal field theory conserves information, then quantum gravity should also conserve information.
Calculations involving gravitational path integrals, which sum over all possible space-time geometries, have proven valuable in understanding the entropy and conservation of information in black holes.
Deep dives
The puzzle of quantum gravity
The podcast discusses the long-standing challenge in physics of reconciling Einstein's general theory of relativity with the principles of quantum mechanics. Experimental guidance is limited, so thought experiments are used to explore the possible nature of quantum gravity.
The black hole information loss puzzle
The podcast introduces the black hole information loss puzzle, which addresses the apparent contradiction between quantum mechanics and the loss of information in black holes. Stephen Hawking's calculations suggest that black holes destroy information, contrary to the conservation of information in most of physics.
The quest to understand black hole information loss
The podcast discusses ongoing research to solve the black hole information loss puzzle. The search for mechanisms that can preserve information in an evaporating black hole is crucial to understanding quantum gravity. Recent developments in this field, including the ADS-CFT correspondence and the calculation of entropy, show promising progress toward resolving the puzzle.
The ADS-CFT correspondence
The podcast explains the ADS-CFT correspondence, which establishes a duality between quantum gravity in anti-de Sitter space and a quantum field theory without gravity. This correspondence has passed non-trivial tests and demonstrates that if a conformal field theory conserves information, then quantum gravity should also conserve information. However, further progress is needed to understand the mechanisms by which information is preserved.
Understanding the behavior of black holes in ADS
The podcast episode discusses the challenge of understanding the evaporation process of black holes in Anti-de Sitter space (ADS) and how physicists were able to compute the entropy of the black hole and radiation. They found that the entropy behavior aligns with the conservation of information, indicating that information is constantly present. This calculation was done in the context of quantum gravity language, which is different from previous evidence based on the ADS/CFT correspondence. This finding was unexpected and exciting, as it provides insights into the conservation of information.
The role of path integrals and gravitational path integrals
The episode explores the concept of path integrals and how they are used in quantum mechanics to calculate the evolution of a wave function. In the context of gravitational path integrals, the calculations involve summing over all possible space-time geometries that have fixed boundaries. These calculations can provide insights into the entropy of black holes and the radiation they produce. Although the exact mechanism by which information gets out of black holes is still unknown, the gravitational path integral has proven to be a valuable tool in understanding information conservation and providing hints towards a complete understanding of quantum gravity.
Stephen Hawking made a number of memorable contributions to physics, but perhaps his greatest was a puzzle: what happens to information that falls into a black hole? The question sits squarely at the overlap of quantum mechanics and gravitation, an area in which direct experimental input is hard to come by, so a great number of leading theoretical physicists have been thinking about it for decades. Now there is a possibility that physicists might have made some progress, by showing how subtle effects relate the radiation leaving a black hole to what’s going on inside. Netta Engelhardt is one of the contributors to these recent advances, and together we go through the black hole information puzzle, why wormholes might be important to the story, and what it all might teach us about quantum gravity.
Netta Engelhardt received her Ph.D. in physics from the University of California, Santa Barbara. She is currently on the faculty in the physics department at MIT. She recently shared the New Horizons in Physics Prize with Ahmed Almheiri, Henry Maxfield, and Geoff Penington, “for calculating the quantum information content of a black hole and its radiation.”