THE BLACK HOLE INFORMATION ESCAPE 6

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he concept of black holes in space has been around since the late 1700’s. It was only later in 1939 that the black hole was theoretically discovered by J. Robert Oppenheimer and Hartland Snyder, who were making use of calculations from Albert Einstein’s theory of general relativity. In 1970 the first physical black hole, Cygnus X-1, was identified. Even though his calculations predicted their existence, Einstein himself did not believe black holes existed. Still, his work and theory of general relativity was revolutionary, it explained gravity as equivalent to acceleration; motion effects time and space, as it should also effect gravity. But where Einstein left off was to confirm the existence of black holes, as well as the physics of this powerful phenomenon.

What was the original idea of your research, ‘Black Hole Evaporation Rates,’ and what came of it?

But before any of that, what is a black hole? According to NASA, a black hole is: “a place in space where gravity pulls so much that even light can not get out. The gravity is so strong because matter has been squeezed into a tiny space. This can happen when a star is dying.” Picking up where Einstein left off, through breakthroughs in different branches of physics and math, specialized technology for space observation, and the constant testing and retesting of theories, some of the unknowns about this vast unknown are on the verge of being unlocked.

MP: “There are few things that you can do with a black hole. To study something you often need to interact with it. To interact with a black hole is almost impossible since anything you send will get trapped there, according to the common wisdom. But, what Hawking shows, and we continue in that tradition, is that energy CAN come out. And you may be able to use this to study and gain more knowledge about black holes.”

Professor Sam Braunstein and Dr. Manas Patr,a at the University of York, UK, saw a chance to uncover another piece of the black hole paradox that so many of the world’s most powerful minds are trying to figure out. The possible implications of their discoveries so far have caused quite a stir. Among other reasons, their work helps support the theory that information can escape black holes, which may eventually help us understand more about gravity, picking up where Newton and Einstein left off.

SB: “One of the reasons you have these paradoxes is that there are lots of plausible arguments that people come up with which can leave you tied in knots. Our approach in many ways seems quite distinct from the conventional picture everyone had of how the evaporation process works.”

SB: “We were really looking just at the problem of information return from what many consider a “toy model” of black hole evaporation. We got so much resistance to that work that we decided to see whether that toy model could really make sensible predictions about a black hole’s spectrum. To our surprise it was right on the money.” MP: “Sam’s idea was that quantum information should apply to black holes as well as atoms, photons, and so on. Our work indicates that this may be true. Even if we are still far from a complete theory, this is a small step.” What is the most difficult aspect of studying black hole physics?

The black hole is often referred to as a paradox, why is it the subject of so many competing theories?

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Theoretical Physicist Erik Verlinde’s work has been praised as picking up where Einstein (and Newton) left off regarding black hole information and gravity. What is significant about his work and how is your work connected to his?

“To interact with a black hole is almost impossible since anything you send will get trapped there, according to the common wisdom.”

Samuel Braunstein was awarded a BSc (Honors) and MSc in Physics from the University of Melbourne and received his PhD in Physics from the California Institute of Technology in 1988. He is editor of three books "Quantum Computing," "Scalable Quantum Computing" and "Quantum Information with Continuous Variables" and serves on the editorial board of the journal Fortschritte der Physik for which he has prepared two special issues on quantum computation. He is the Founder and Managing Editor of Quantum Information and Computation -- the first journal dedicated specifically to this field.

SB: “Verlinde and others have been looking at something interesting about gravity; they point to Ted Jacobsen who had an article that he published in 1995, which shows something really remarkable. If we take the change in entropy of a system (as heat flux divided by the temperature) if you apply that simple thermodynamic relation to all possible event horizons, you end up reproducing the full structure of the Einstein equations of gravity. This eventually led to the suggestion that gravity, spacetime and inertia, might be emergent from an underlying thermodynamic theory. This reasoning might allow you to understand why things have mass and where gravitational attraction comes from. According to Verlinde both these things come from the thermodynamic properties across horizons. However, traditionally, these thermodynamic properties of horizons are derived from the full properties of curved space-time and gravity. So Verlinde’s ideas might just be interpreted as a logical consistency and no more. Our work shows that you can break that mutual implication, since the thermal properties of event horizons do not need space or time or any of the usual stuff from general relativity.” We often say that in hard sciences there are more definite answers compared to, say, the humanities. But it seems with the work you’re doing related to black hole physics there are a lot of disagreements and versions of answers. SB: “In science we have a lot of these in between areas where we don’t necessarily have explicit calculations, and we rely on a sort of folklore. This

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folklore can be quite old with origins and logic behind it that are lost, and it isn’t always right. Bit by bit we uncover that in fact you can do things that you might have thought were impossible. Like being able to image things significantly smaller than a wavelength, a feat which used to be considered impossible.”

“In science we have a lot of these in between areas where we don’t necessarily have explicit calculations, and we rely on a sort of folklore.”

How close are we to having one undisputed theory? MP: “It is very hard to get out of a 300-400 year belief system. Since the days of Newton we believe that gravity is the most universal and fundamental force. Unless we have a complete and consistent theory which would recreate the work of Einstein and Newton, only then can we convince the larger community that this is the new thing. Gravity has been around since Newton’s time, 300 years. Quantum theory is about 100 years or less. Until we’ve combined quantum theory and gravity, a unified approach, which may or may not be possible, I think it’s still a long road. What we think is that quantum information should play a role in any kind of unifying theory.” BY MARK FONSECA RENDEIRO

Manas Patra did his undergraduate and postgraduate studies in the University of Delhi (St. Stephen’s College). His PhD work in the physics department of the University was in mathematical physics. Since 2008 he has been with the Department of Computer Science, University of York. Dr. Patra has published papers in physics, mathematical physics and computer science. He has a wide range of interests in physics, computer science and mathematics. His research interests include quantum information science, quantum computing, quantum optics, logic and complexity, quantum foundations, black hole physics, classical and quantum gravity and algebraic quantum theory. 9

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GENERAL RELATIVITY The theory of gravitation, developed by Einstein, says that the observed gravitational attraction between masses results from their warping of space and time. EVENT HORIZON In general relativity, an event horizon the boundary in spacetime beyond which events cannot affect an outside observer. In layman’s terms it is defined as “the point of no return” i.e. the point at which the gravitational pull becomes so great as to make escape impossible. HEAT FLUX The rate of heat energy transfer through a given surface. HAWKING RADIATION Hawking radiation is a thermal radiation with a black body spectrum predicted to be emitted by black holes due to quantum effects. BLACK HOLE EVAPORATION The Hawking radiation process reduces the mass and the energy of the black hole. This phenomenon is known as black hole evaporation. INERTIA The idea that an object keeps moving unless acted upon by an outside force. ENTROPY The idea that nature tends to move from order to disorder in isolated systems.

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