Quantum theory of universe
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Quantum Theory of the Universe: A Comprehensive Overview
Introduction to Quantum Cosmology
Quantum cosmology applies quantum physics principles to the entire universe, aiming to understand its origin, structure, and dynamics. This field, though not yet fully defined, raises significant conceptual, mathematical, and physical questions. Unlike traditional approaches that simplify the universe to a few degrees of freedom (minisuperspace), modern quantum cosmology emphasizes the interaction of numerous microscopic degrees of freedom that describe spacetime geometry, drawing parallels with systems in condensed-matter and particle physics .
Quantum Creation and the Universe's Origin
The concept of the universe's creation as a quantum phenomenon suggests that massy particles can be created without energy cost in a cosmological context. This leads to a model where the universe emerges from a spontaneous disturbance, avoiding the initial singularity associated with the Big Bang. Instead, the universe's history is divided into a creation phase, resulting in a "fireball," followed by a phase of free expansion .
Universality of Quantum Theory
Quantum theory is argued to be universally applicable, even to the universe as a whole. This universality, combined with the emergence of classical behaviors through decoherence, supports the application of quantum principles to cosmology. This approach also addresses the unresolved problem of quantum gravity, integrating quantum cosmology into the broader framework of quantum theory .
Bayesian Probability in Quantum Theory
A novel approach to quantum cosmology uses Bayesian probability to define the universe's probability. Unlike frequency probability, Bayesian probability can describe events that occur only once. This method has been applied to scalar field theory, providing explicit probabilities and actions for the universe's matter .
Quantum Multiverses
Quantum cosmology predicts the existence of quantum multiverses, which are sets of alternative histories describing the evolution of spacetime and matter. These multiverses arise naturally from the quantum dynamics and state of the universe, offering mechanisms for varying constants in effective theories and enabling anthropic selection. Different levels of coarse-grained multiverses provide various routes for calculation, supported by decoherence .
Interpretation of Quantum Mechanics
A new interpretation of quantum mechanics posits that the universe's state is a consistent set of facts, with relationships between objects storing and instantiating these facts. Quantum superpositions exist only if the universe's facts are consistent with them. This interpretation suggests that quantum mechanics, Planck's constant, and spacetime discretization are emergent phenomena from a more fundamental ontology .
Quantum Theory from Quantum Gravity
Quantum theory can emerge from a background-independent model without inherent quantum mechanics. By starting with an abstract graph as the microscopic model of spacetime, it is shown that the probability distributions of certain functions evolve according to the Schrödinger equation. This approach links nonlocal hidden variables to the fundamental graph's structure, transferring stochastic fluctuations into universal quantum fluctuations .
The Undivided Universe
David Bohm and Basil Hiley's ontological interpretation of quantum theory presents a coherent notion of the universe's reality without relying on the observer's role. This interpretation, which includes concepts like active information and non-locality, addresses paradoxes in standard quantum mechanics, such as wave-particle duality and wave function collapse. It suggests areas where quantum theory might break down, allowing for empirical tests .
Conclusion
Quantum cosmology offers a rich and complex framework for understanding the universe through quantum principles. From the creation of the universe to the interpretation of quantum mechanics, this field integrates various approaches and theories, highlighting the need for further research and development. The insights gained from quantum cosmology not only advance our understanding of the universe but also challenge and refine the foundations of quantum theory itself.
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