In terms of classical physics, the physical reality may be defined as matter and energy behaving according to the laws of physics in classical spacetime, and the human being is a passive observer of this reality. According to quantum physics, matter and energy behave according to the laws of quantum physics in quantized spacetime, and the human observer is an integral part of this reality: The quantum physics include consciousness as an integral part of its laws.
In this book the author discusses the deficiencies of two major interpretations of quantum physics: The Copenhagen interpretation expounded by Niels Bohr and the Many worlds' interpretation proposed by Hugh Everett III. The author also discusses a third hypothesis called the consistent histories approach. The book starts with a traditional text book style introduction to Young's double slit experiments. In a popular book such as this, it is a turn off, because an ordinary reader would like to read more about the descriptive part rather than the experimental part. Complicating this further, some chapters require reasonable knowledge of physics and mathematics and an interest in experimental physics to appreciate the subject matter.
The quantum physical problem arises from how elementary particles at the microscopic level (quantum physics) are measured from the macroscopic instruments (classical physics). In the quantum world, an elementary particle or a collection of such particles can exist in a superposition of two or more possible states of physical being. It can be in a superposition of different locations, velocities and orientations of its spin anywhere in the universe, but when we measure one of these properties we see one of the elements of the superposition, but not a combination of them. The measuring macroscopic object will not be in this superposition. How do we explain this unique world of reality emerge from the multiplicities of alternative superposed quantum states? The wave functions that represent each quantum state treat each element of the superposition as equally real (but not necessarily equally probable.)
The Schrödinger equation delineates how a quantum system's wave function will change through time. This predicts a smooth and deterministic (no randomness) change. But mathematics contradicts this when humans observe a quantum system with an instrument. At the moment of measurement, the wave function describing the superposition of all states collapse into one member of the superposition, thus interrupting the smooth evolution of the wave function and introducing discontinuity in the system. The selected state at the moment of measurement is arbitrary, and its emergence does not evolve logically from the information packed wave function of the particle. In addition, the mathematics of collapse does not emerge from the seamless flow of the Schrödinger equation, but collapse has to be added as an additional process that seems to violate the equation. This is the main argument of the Copenhagen interpretation. This approach privileges the external observer in a classical realm distinct from the quantum realm of the object observed and the nature of the boundary between the quantum and classical realms remains unclear.
The Many worlds' interpretation addresses precisely this point by merging the microscopic and macroscopic worlds, thus making the observer an integral part of the quantum system. A universal wave function links macroscopic observers and microscopic objects as a part of a single quantum system, which would introduce a discontinuity in the wave-function collapse. Conversely, if we assume the continuous evolution of wave functions is not interrupted by the act of measurement. And if the Schrödinger equation holds good even for objects and observers alike with no elements of superposition banished from reality. Under these circumstances the wave function of an observer would, in effect, bifurcate at each interaction of the observer with a superposed object. The universal wave function would contain branches for every alternative making up the object's superposition. Each branch has its own copy of the observer, a copy that perceived one of those alternatives as the outcome (resulting in multiple universes). According to a fundamental mathematical property of the Schrödinger equation, once formed, the branches do not influence one another. Thus, each branch (universe) embarks on a different future, independently of the others.
The consistent histories is based on a consistency criterion that allows the history of a system to be described such that the probabilities for each history obey the rules of classical probability while being consistent with Schrodinger's equation. It turns out that none of these theories are completely satisfactory. At the end of the book, the author expresses hope that sometime in future, quantum physics will be able to distinguish the illusion and physical realty. This is farfetched because there is a growing consensus among many physicists that the answers to the problems in quantum reality may be found in string physics such as superstring theory or brane physics, and not through the unification of quantum physics with classical physics. Some physicists even believe that the unification of the two theories with respect to the gravitational force is inherently problematic if not impossible.
In this book the author discusses the deficiencies of two major interpretations of quantum physics: The Copenhagen interpretation expounded by Niels Bohr and the Many worlds' interpretation proposed by Hugh Everett III. The author also discusses a third hypothesis called the consistent histories approach. The book starts with a traditional text book style introduction to Young's double slit experiments. In a popular book such as this, it is a turn off, because an ordinary reader would like to read more about the descriptive part rather than the experimental part. Complicating this further, some chapters require reasonable knowledge of physics and mathematics and an interest in experimental physics to appreciate the subject matter.
The quantum physical problem arises from how elementary particles at the microscopic level (quantum physics) are measured from the macroscopic instruments (classical physics). In the quantum world, an elementary particle or a collection of such particles can exist in a superposition of two or more possible states of physical being. It can be in a superposition of different locations, velocities and orientations of its spin anywhere in the universe, but when we measure one of these properties we see one of the elements of the superposition, but not a combination of them. The measuring macroscopic object will not be in this superposition. How do we explain this unique world of reality emerge from the multiplicities of alternative superposed quantum states? The wave functions that represent each quantum state treat each element of the superposition as equally real (but not necessarily equally probable.)
The Schrödinger equation delineates how a quantum system's wave function will change through time. This predicts a smooth and deterministic (no randomness) change. But mathematics contradicts this when humans observe a quantum system with an instrument. At the moment of measurement, the wave function describing the superposition of all states collapse into one member of the superposition, thus interrupting the smooth evolution of the wave function and introducing discontinuity in the system. The selected state at the moment of measurement is arbitrary, and its emergence does not evolve logically from the information packed wave function of the particle. In addition, the mathematics of collapse does not emerge from the seamless flow of the Schrödinger equation, but collapse has to be added as an additional process that seems to violate the equation. This is the main argument of the Copenhagen interpretation. This approach privileges the external observer in a classical realm distinct from the quantum realm of the object observed and the nature of the boundary between the quantum and classical realms remains unclear.
The Many worlds' interpretation addresses precisely this point by merging the microscopic and macroscopic worlds, thus making the observer an integral part of the quantum system. A universal wave function links macroscopic observers and microscopic objects as a part of a single quantum system, which would introduce a discontinuity in the wave-function collapse. Conversely, if we assume the continuous evolution of wave functions is not interrupted by the act of measurement. And if the Schrödinger equation holds good even for objects and observers alike with no elements of superposition banished from reality. Under these circumstances the wave function of an observer would, in effect, bifurcate at each interaction of the observer with a superposed object. The universal wave function would contain branches for every alternative making up the object's superposition. Each branch has its own copy of the observer, a copy that perceived one of those alternatives as the outcome (resulting in multiple universes). According to a fundamental mathematical property of the Schrödinger equation, once formed, the branches do not influence one another. Thus, each branch (universe) embarks on a different future, independently of the others.
The consistent histories is based on a consistency criterion that allows the history of a system to be described such that the probabilities for each history obey the rules of classical probability while being consistent with Schrodinger's equation. It turns out that none of these theories are completely satisfactory. At the end of the book, the author expresses hope that sometime in future, quantum physics will be able to distinguish the illusion and physical realty. This is farfetched because there is a growing consensus among many physicists that the answers to the problems in quantum reality may be found in string physics such as superstring theory or brane physics, and not through the unification of quantum physics with classical physics. Some physicists even believe that the unification of the two theories with respect to the gravitational force is inherently problematic if not impossible.
Reference: Quantum Physics: Illusion or Reality? By Alastair I. M. Rae
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