Black holes, some of the most peculiar objects in the universe, pose a paradox for physicists. Two of our best theories give us two differentand seemingly contradictorypictures of how these objects work. Many scientists, including myself, have been trying to reconcile these visions, not just to understand black holes themselves, but also to answer deeper questions, such as What is spacetime? While I and other researchers made some partial progress over the years, the problem persisted. In the past year or so, however, I have developed a framework that I believe elegantly addresses the problem and gives us a glimpse of the mystery of how spacetime emerges at the most fundamental level.
Here is the problem: From the perspective of general relativity, black holes arise if the density of matter becomes too large and gravity collapses the material all the way toward its central point. When this happens, gravity is so strong in this region that nothingeven lightcan escape. The inside of the black hole, therefore, cannot be seen from the outside, even in principle, and the boundary, called the event horizon, acts as a one-way membrane: nothing can go from the interior to the exterior, but there is no problem in falling through it from the exterior to the interior.
But when we consider the effect of quantum mechanics, the theory governing elementary particles, we get another picture. In 1974, Stephen Hawking presented a calculation that made him famous. He discovered that, if we include quantum mechanical effects, a black hole in fact radiates, although very slowly. As a result, it gradually loses its mass and eventually evaporates. This conclusion has been checked by multiple methods now, and its basic validity is beyond doubt. The odd thing, however, is that in Hawkings calculation, the radiation emitted from a black hole does not depend on how the object was created. This means that two black holes created from different initial states can end up with the identical final radiation.
Is this a problem? Yes, it is. Modern physics is built on the assumption that if we have perfect knowledge about a system, then we can predict its future and infer its past by solving the equation of motion. Hawkings result would mean that this basic tenet is incorrect. Many of us thought that this problem was solved in 1997 when Juan Maldacena discovered a new way to view the situation, which seemed to prove no information was lost.
Case closed? Not quite. In 2012, Ahmed Almheiri and collaborators at the University of California, Santa Barbara, presented in their influential paper a strong argument that if the information is preserved in the Hawking emission process, then it is inconsistent with the smoothness of the horizonthe notion that an object can pass through the event horizon without being affected. Given that the option of information loss is out of the question, they argued that the black hole horizon is in fact not a one-way membrane but something like an unbreakable wall, which they called a firewall.
This confused theorists tremendously. As much as they disliked information loss, they abhorred firewalls too. Among other things, the firewall idea implies that Einsteins general relativity is completely wrong, at least at the horizon of a black hole. In fact, this is utterly counterintuitive. For a large black hole, gravity at the horizon is actually very weak because it lies far away from the central point, where all the matter is located. A region near the horizon thus looks pretty much like empty space, and yet the firewall argument says that space must abruptly end at the location of the horizon.
The main thrust of my new work is to realize that there are multiple layers of descriptions of a black hole, and the preservation of information and the smoothness of the horizon refer to theories at different layers. At one level, we can describe a black hole as viewed from a distance: the black hole is formed by collapse of matter, which eventually evaporates leaving the quanta of Hawking radiation in space. From this perspective, Maldacenas insight holds and there is no information loss in the process. That is because, in this picture, an object falling toward the black hole never enters the horizon, not because of a firewall but because of time delay between the clock of the falling object and that of a distant observer. The object seems to be slowly absorbed into the horizon, and its information is later sent back to space in the form of subtle correlations between particles of Hawking radiation.
On the other hand, the picture of the black hole interior emerges when looking at the system from the perspective of someone falling into it. Here we must ignore the fine details of the system that an infalling observer could not see because he or she has only finite time until they hit the singular point at the center of the black hole. This limits the amount of information they can access, even in principle. The world the infalling observer perceives, therefore, is the coarse-grained one. And in this picture, information need not be preserved because we already threw away some information even to arrive at this perspective. This is the way the existence of interior spacetime can be compatible with the preservation of information: they are the properties of the descriptions of nature at different levels!
To understand this concept better, the following analogy might help. Imagine water in a tank and consider a theory describing waves on the surface. At a fundamental level, water consists of a bunch of water molecules, which move, vibrate and collide with each other. With perfect knowledge of their properties, we can describe them deterministically without information loss. This description would be complete, and there would be no need to even introduce the concept of waves. On the other hand, we could focus on the waves by overlooking molecular level details and describing the water as a liquid. The atomic-level information, however, is not preserved in this description. For example, a wave can simply disappear, although the truth is that the coherent motion of water molecules that created the wave was transformed into a more random motion of each molecule without anything disappearing.
This framework tells us that the picture of spacetime offered by general relativity is not as fundamental as we might have thoughtit is merely a picture that emerges at a higher level in the hierarchical descriptions of nature, at least concerning the interior of a black hole. Similar ideas have been discussed earlier in varying forms, but the new framework allows us to explicitly identify the relevant microscopic degrees of freedomin other words, nature's fundamental building blocksparticipating in the emergence of spacetime, which surprisingly involves elements that we normally think to be located far away from the region of interest.
This new way of thinking about the paradox can also be applied to a recent setup devised by Geoff Penington, Stephen H. Shenker, Douglas Stanford and Zhenbin Yang in which Maldacenas scenario is applied more rigorously but in simplified systems. This allows us to identify which features of a realistic black hole are or are not captured by such analyses.
Beginning with the era of Descartes and Galilei, revolutions in physics have often been associated with new understandings of the concept of spacetime, and it seems that we are now in the middle of another such revolution. I strongly suspect that we may soon witness the emergence of a new understanding of nature at a qualitatively different and deeper level.
Read more:
Have We Solved the Black Hole Information Paradox? - Scientific American
- The application of three-axis low energy spectroscopy in quantum physics research - Phys.Org - May 3rd, 2017 [May 3rd, 2017]
- Physicists breed Schrdinger's cats to find boundaries of the | Cosmos - Cosmos - May 3rd, 2017 [May 3rd, 2017]
- Scientists 'BREED' Schrodinger's Cat in massive quantum physics breakthrough - Express.co.uk - May 3rd, 2017 [May 3rd, 2017]
- Quantum Physics: Are Entangled Particles Connected Via An Undetected Dimension? - Forbes - May 3rd, 2017 [May 3rd, 2017]
- Quantum physics is oppressive - Patheos - Patheos (blog) - June 6th, 2017 [June 6th, 2017]
- It's widely abused as a buzzword. But can quantum mechanics explain how we think? - National Post - June 6th, 2017 [June 6th, 2017]
- Quantum Physics and Love are Super Weird and Confusing, but This Play Makes Sense of Them Both - LA Magazine - June 6th, 2017 [June 6th, 2017]
- One step closer to the quantum internet by distillation - Phys.Org - June 7th, 2017 [June 7th, 2017]
- UW Grad Student from Star Valley Earns Quantum Mechanics Fellowship - SweetwaterNOW.com - June 10th, 2017 [June 10th, 2017]
- Solving systems of linear equations with quantum mechanics - Phys.Org - June 10th, 2017 [June 10th, 2017]
- Quantum Computing Might Be Here Sooner Than You Think ... - Bloomberg - June 14th, 2017 [June 14th, 2017]
- Quantum Physics News - Phys.org - News and Articles on ... - June 14th, 2017 [June 14th, 2017]
- Chinese satellite breaks a quantum physics record, beams entangled photons from space to Earth - Los Angeles Times - June 16th, 2017 [June 16th, 2017]
- Popular Quantum Physics Books - Goodreads - June 16th, 2017 [June 16th, 2017]
- Cybersecurity Attacks Are a Global Threat. Chinese Scientists Have the Answer: Quantum Mechanics - Newsweek - June 17th, 2017 [June 17th, 2017]
- A quantum step to a great wall for encryption - The Hindu - June 18th, 2017 [June 18th, 2017]
- What Is Quantum Mechanics? - livescience.com - June 18th, 2017 [June 18th, 2017]
- Physicists Demonstrate Record Breaking Long-Distance Quantum Entanglement in Space - Futurism - June 20th, 2017 [June 20th, 2017]
- Viewpoint: A Roadmap for a Scalable Topological Quantum Computer - Physics - June 21st, 2017 [June 21st, 2017]
- How Schrdinger's Cat Helps Explain the New Findings About the Quantum Zeno Effect - Futurism - June 21st, 2017 [June 21st, 2017]
- BMW and Volkswagen Try to Beat Apple and Google at Their Own Game - New York Times - June 22nd, 2017 [June 22nd, 2017]
- How quantum physics could revolutionize casinos and betting if you can understand it - Casinopedia - June 22nd, 2017 [June 22nd, 2017]
- Quantum thermometer or optical refrigerator? - Phys.Org - June 22nd, 2017 [June 22nd, 2017]
- Physicists settle debate over how exotic quantum particles form - Phys.Org - June 23rd, 2017 [June 23rd, 2017]
- In 1928, One Physicist Accidentally Predicted Antimatter - Popular Mechanics - June 23rd, 2017 [June 23rd, 2017]
- Atomic imperfections move quantum communication network closer ... - Phys.Org - June 24th, 2017 [June 24th, 2017]
- DOE Launches Chicago Quantum Exchange - HPCwire (blog) - June 26th, 2017 [June 26th, 2017]
- Google to Achieve "Supremacy" in Quantum Computing by the End of 2017 - Big Think - June 26th, 2017 [June 26th, 2017]
- Physicists make quantum leap in understanding life's nanoscale ... - Phys.Org - June 27th, 2017 [June 27th, 2017]
- Berkeley Lab Intern Finds Her Way in Particle Physics - Lawrence Berkeley National Laboratory - June 27th, 2017 [June 27th, 2017]
- Payments Innovation - A Quantum World Of Payments - Finextra (blog) - June 30th, 2017 [June 30th, 2017]
- Why can't quantum theory and relativity get along? - Brantford Expositor - June 30th, 2017 [June 30th, 2017]
- How quantum trickery can scramble cause and effect - Nature.com - June 30th, 2017 [June 30th, 2017]
- Telecommunications, Meet Quantum Physics - Electronics360 - June 30th, 2017 [June 30th, 2017]
- Stephen Colbert Gets a Lesson on Quantum Physics from Brian ... - Patheos (blog) - July 2nd, 2017 [July 2nd, 2017]
- Quantum physics for babies a different bedtime story - CBC.ca - August 24th, 2017 [August 24th, 2017]
- How quantum mechanics can change computing - San Francisco ... - San Francisco Chronicle - August 24th, 2017 [August 24th, 2017]
- Physicists Use Lasers to Set Up First Underwater Quantum Communications Link - Gizmodo - August 24th, 2017 [August 24th, 2017]
- Notable Quotes on Quantum Physics Quantum Enigma - February 15th, 2018 [February 15th, 2018]
- Nothing Is Solid & Everything Is Energy Scientists Explain The World ... - April 11th, 2018 [April 11th, 2018]
- The World Of Quantum Physics: EVERYTHING Is Energy - In5D ... - April 22nd, 2018 [April 22nd, 2018]
- Nothing Is Solid & Everything Is Energy Scientists ... - May 1st, 2018 [May 1st, 2018]
- Black Holes Bolster Case For Quantum Physics' Spooky Action ... - August 29th, 2018 [August 29th, 2018]
- Physics4Kids.com: Modern Physics: Quantum Mechanics - September 29th, 2018 [September 29th, 2018]
- Quantum Theory - Full Documentary HD - November 6th, 2018 [November 6th, 2018]
- Quantum mind - Wikipedia - February 6th, 2019 [February 6th, 2019]
- What is quantum theory? - Definition from WhatIs.com - May 5th, 2019 [May 5th, 2019]
- The Ultimate Mystery? Consciousness May Exist in the Absence of Matter (Weekend Feature) - The Daily Galaxy --Great Discoveries Channel - September 19th, 2019 [September 19th, 2019]
- Faculty Opening, Quantum Information and Condensed Matter Experiment - Physics - September 19th, 2019 [September 19th, 2019]
- Become the physicists the world needs with the help of a physics degree - Study International News - September 19th, 2019 [September 19th, 2019]
- Imec and NUS working on chip-based quantum cryptography - Optics.org - September 19th, 2019 [September 19th, 2019]
- Strong LightMatter Coupling in Molecular and Material Engineering - Advanced Science News - September 19th, 2019 [September 19th, 2019]
- The key to bigger quantum computers could be to build them like Legos - MIT Technology Review - September 19th, 2019 [September 19th, 2019]
- Australian universities are accused of trading free speech for cash - The Economist - September 19th, 2019 [September 19th, 2019]
- APS Physics Career Center - Physics - September 19th, 2019 [September 19th, 2019]
- Assistant Professor of Physics, Employment - Physics - September 19th, 2019 [September 19th, 2019]
- A new approach to quantum gravity - Tech Explorist - September 19th, 2019 [September 19th, 2019]
- A Huge Experiment Has 'Weighed' the Tiny Neutrino, a Particle That Passes Right Through Matter - Gizmodo - September 19th, 2019 [September 19th, 2019]
- Many Worlds, But Too Much Metaphor - Forbes - September 19th, 2019 [September 19th, 2019]
- Iran to open 1st quantum physics lab in a year: AEOI head - Mehr News Agency - English Version - September 19th, 2019 [September 19th, 2019]
- Quantum Computing Breakthrough: New Detection Tool Uncovers Noise That Can Kill Qubits - SciTechDaily - September 19th, 2019 [September 19th, 2019]
- A quantum computing startup that spun out of a Harvard lab just came out of stealth mode with $2.7 million in seed funding from investors like Samsung... - September 19th, 2019 [September 19th, 2019]
- Important Quantum Algorithm May Be a Property of Nature - Technology Networks - September 19th, 2019 [September 19th, 2019]
- A New Perspective On Grover's Search Algorithm -- Quantum Physics & DNA - Analytics India Magazine - September 19th, 2019 [September 19th, 2019]
- Iran to open first quantum physics lab in a year: AEOI head - Quantaneo, the Quantum Computing Source - September 19th, 2019 [September 19th, 2019]
- Sean Carroll: Universe a 'tiny sliver' of all there is - PBS NewsHour - September 19th, 2019 [September 19th, 2019]
- IBM cuts ribbon on quantum computing centre wherein a 53-qubit monster lurks - The Register - September 19th, 2019 [September 19th, 2019]
- In 'Something Deeply Hidden,' Sean Carroll Argues There Are Infinite Copies Of You - NPR - September 19th, 2019 [September 19th, 2019]
- Physicists race to develop room-temperature quantum chips - The Next Web - September 19th, 2019 [September 19th, 2019]
- This One Experiment Reveals More About Reality Than Any Quantum Interpretation Ever Will - Forbes - September 19th, 2019 [September 19th, 2019]
- Our world is in need of the Mahatmas teachings: Dalai Lama - Livemint - October 2nd, 2019 [October 2nd, 2019]
- Quantum-inspired Beckman Institute celebration will be anything but small - Central Illinois Buzz - October 2nd, 2019 [October 2nd, 2019]
- Is It a Wave or a Particle? It's Both, Sort Of. - Space.com - October 2nd, 2019 [October 2nd, 2019]
- Princeton announces initiative to propel innovations in quantum science and technology - Quantaneo, the Quantum Computing Source - October 2nd, 2019 [October 2nd, 2019]
- Precision physics with 'tabletop' experiments - Stanford University News - October 2nd, 2019 [October 2nd, 2019]
- Andrea Young uncovers the strange physics of 2-D materials - Science News - October 2nd, 2019 [October 2nd, 2019]
- A Scientific Explainer of What Terrence Howard Was Talking About at the Emmys - VICE - October 2nd, 2019 [October 2nd, 2019]
- China's Silicon Valley aims to become the country's top research center - Abacus - October 16th, 2019 [October 16th, 2019]
- New Quantum-Mechanical Dissipation Mechanism Observed for the First Time - SciTechDaily - October 16th, 2019 [October 16th, 2019]
- Physicists have found quasiparticles that mimic hypothetical dark matter axions - Science News - October 16th, 2019 [October 16th, 2019]