We discuss an apparent information paradox that arises in a materialist’s description of the Universe if we assume that the Universe is 100% quantum. We discuss possible ways out of the paradox, including that Laws of Nature are not purely deterministic, or that gravity is classical. Our observation of the paradox stems from an interdisciplinary thought process whereby the Universe can be viewed as a “quantum computer”. Our presentation is intentionally nontechnical to make it accessible to as wide a readership base as possible.
We discuss an apparent information paradox that arises in a materialist’s description of the Universe if we assume that the Universe is 100% quantum. We discuss possible ways out of the paradox, including that Laws of Nature are not purely deterministic, or that gravity is classical. Our observation of the paradox stems from an interdisciplinary thought process whereby the Universe can be viewed as a “quantum computer”. Our presentation is intentionally nontechnical to make it accessible to as wide a readership base as possible.
We discuss an apparent information paradox that arises in a materialist's description of the Universe if we assume that the Universe is 100% quantum.We discuss possible ways out of the paradox, including that Laws of Nature are not purely deterministic, or that gravity is classical.Our observation of the paradox stems from an interdisciplinary thought process whereby the Universe can be viewed as a "quantum computer".Our presentation is intentionally nontechnical to make it accessible to as wide a readership base as possible.
Copenhagen is the perfect setting for our discussion of matter and information. We have been charged ‘to explore the current concept of matter from scientific, philosophical, and theological perspectives’. The essential foundation for this work is the output of the intense intellectual struggles that took place here in Copenhagen during the twenties, principally between Niels Bohr, Werner Heisenberg, and Wolfgang Pauli. Those struggles replaced the then-prevailing Newtonian idea of matter as ‘solid, massy, hard, impenetrable, moveable particles’ with a new concept that allowed, and in fact demanded, entry into the laws governing the motion of matter of the consequences of decisions made by human subjects. This change in the laws swept away the meaningless billiard-ball universe, and replaced it with a universe in which we human beings, by means of our intentional effort, can make a difference in how the ‘matter’ in our bodies behaves. The role of mind in nature Unfortunately, most of the prevailing descriptions of quantum theory tend to emphasize puzzles and paradoxes in a way that makes philosophers, theologians, and even non-physicist scientists leery of actually using in any deep way the profound changes in our understanding of human beings in nature wrought by the quantum revolution. Yet, properly presented, quantum mechanics is thoroughly in line with our deep human intuitions. It is the 300 years of indoctrination with basically false ideas about how nature works that now makes puzzling a process that is completely in line with normal human intuition. I therefore begin with a non-paradox-laden description of the quantum universe and the place of our minds within it.
Thirty years ago, John Preskill concluded "that the information loss paradox may well presage a revolution in fundamental physics" and mused that "Conceivably, the puzzle of black hole evaporation portends a scientific revolution as sweeping as that that led to the formulation of quantum theory in the early 20th century." Many still agree with this assessment. On the other hand, it seems to me the "paradox" has little to do with the physical world but rather, at best, simply points out the possible inconsistency of two, already disparate, theories (mathematical models) of nature, general relativity and quantum mechanics, with virtually no conceivable observational consequences. The information paradox hinges on the concepts of a pure quantum state, the unitarity of quantum mechanics, and Hawking's semi-classical calculation of black hole evaporation. I used the qualifier "at best" above because, for me, the concept of a quantum state is far more restrictive than required by the paradox while unitarity is not a property of nature but rather of a mathematical model and is already violated by the process of making a measurement. Furthermore, the semi-classical calculation of Hawking is surely of limited applicability.
Information is physical: the laws which govern its encoding, processing and communication are bound by those of its unavoidably physical embodiment. In today's informatics, information obeys the laws of Newton's and Maxwell's classical physics: this assertion holds all the way from commercial computers down to (up to?) their most abstract models, e.g. Turing machines and lambda-calculus. Today's computation and communication are classical. Research in quantum information processing and communication was born some twenty five years ago, as a child of two major scientific achievements of the 20th century, namely quantum physics and information sciences. The driving force of this interdisciplinary research is that of looking for the consequences of having information encoding, computation and communication based upon the laws of quantum physics, i.e. the ultimate knowledge that we have, today, of the foreign world of elementary particles, as described by quantum mechanics. Breakthroughs in cryptography, communications, information theory, algorithmics and, more recently, in abstract computational models, programming languages and semantics frameworks, have shown that this transplantation of information from classical to quantum has far reaching consequences, both quantitative and qualitative, and opens new avenues for research within the foundations of computer science.From a computer scientist's point of view, which is my point of view, I will explain the basics, survey the main achievements, and outline the current hot topics and major challenges of this promising and stimulating research. I will not assume any prior knowledge in quantum mechanics from the audience.
Copenhagen is the perfect setting for our discussion of matter and information. We have been charged ‘to explore the current concept of matter from scientific, philosophical, and theological perspectives’. The essential foundation for this work is the output of the intense intellectual struggles that took place here in Copenhagen during the twenties, principally between Niels Bohr, Werner Heisenberg, and Wolfgang Pauli. Those struggles replaced the then-prevailing Newtonian idea of matter as ‘solid, massy, hard, impenetrable, moveable particles’ with a new concept that allowed, and in fact demanded, entry into the laws governing the motion of matter of the consequences of decisions made by human subjects. This change in the laws swept away the meaningless billiard-ball universe, and replaced it with a universe in which we human beings, by means of our intentional effort, can make a difference in how the ‘matter’ in our bodies behaves. THE ROLE OF MIND IN NATURE Unfortunately, most of the prevailing descriptions of quantum theory tend to emphasize puzzles and paradoxes in a way that makes philosophers, theologians, and even non-physicist scientists leery of actually using in any deep way the profound changes in our understanding of human beings in nature wrought by the quantum revolution. Yet, properly presented, quantum mechanics is thoroughly in line with our deep human intuitions. It is the 300 years of indoctrination with basically false ideas about how nature works that now makes puzzling a process that is completely in line with normal human intuition.
In semiclassical gravity, the final state of black-hole evaporation cannot be described by a pure state. Nevertheless, we point out that the system can be described by a generalized pure state, which is not defined on a three-dimensional hypersurface but on the four-dimensional spacetime describing the whole Universe at all times. Unlike the conventional quantum state, such a generalized state treats time on an equal footing with space, which makes it well suited for systems that are both quantum and relativistic. In particular, such a generalized state contains a novel type of information encoded in the correlations between future and past, which avoids the black-hole information paradox.