Time and universe
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Understanding Time and the Universe
The Block Universe and Evolving Block Universe
The concept of the Block Universe suggests that spacetime is a fixed entity where the flow of time is an illusion, and the entire universe exists as a static whole. This view is based on time-reversible microphysical laws but fails to account for the time-irreversible macro-physical behavior and the development of complex systems, such as life. To address these shortcomings, the Evolving Block Universe model has been proposed. This model posits that spacetime itself evolves, with the future continually becoming the past, and the entities within it also evolving over time 13.
Cosmic Time and the Initial State of the Universe
In the context of canonical gravity, the Hamiltonian constraint solution reveals a synergy between gravitation and the intrinsic cosmic clock of our expanding universe. This intrinsic time geometrodynamics shifts the focus from four-dimensional covariance to spatial diffeomorphism invariance, making causal time-ordering and quantum evolution in cosmic time meaningful. The addition of a Cotton–York term to the physical Hamiltonian significantly alters the initial data problem, supporting the idea of the universe originating from a low-entropy hot smooth state, consistent with Penrose’s Weyl Curvature Hypothesis .
Quantum Theory of Time and Human Experience
Recent advances in quantum theory challenge the traditional view of time as a fundamental aspect of the universe. The new quantum theory of time suggests that dynamics may be a phenomenological consequence of a fundamental violation of time reversal symmetry. This theory aligns with the Block Universe view and explores the human experience of existing in the present moment, reflecting on the past, and contemplating the future .
Space-Time Quantization and Universe Dynamics
Space and time are considered forms of material existence in the universe, possessing a quantum character due to the dialectic relationship between attraction and expansion, continuity and discreteness. The universe's time is quantified by cosmic quantum jumps, allowing transitions between quantum levels without singularities. This pulsating nature of the universe provides insights into the fundamental nature of gravity, the speed of light, and the gravitational constant .
Non-Commutative Cosmological Time
A novel proposition is that cosmological time is a quantum observable that does not commute with other essential quantum operators, such as the cosmological constant. This non-commutative property suggests that the universe may be "delocalized" in time, opening up new cosmological scenarios and invalidating several paradoxes. In some models, localized histories emerge through backward transitions in quantum time, akin to a time machine cycle .
Time in Cosmology
In cosmology, time is understood through the transition matrix elements of radiative processes. Classical physics defines time in terms of correlations between successive configurations and a standard trajectory called the clock. In quantum theory, the WKB approximation for the wave function of the scale factor is used, leading to time-dependent quantum amplitudes determined by the total energy of matter .
Conclusion
The study of time and the universe encompasses various models and theories, from the static Block Universe to the dynamic Evolving Block Universe, and from classical to quantum perspectives. These models provide different insights into the nature of time, the evolution of the universe, and the interplay between space, time, and matter. Understanding these concepts is crucial for advancing our knowledge of the cosmos and our place within it.
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Most relevant research papers on this topic
A Universe that Does Not Know the Time
The universe may be "delocalized" in time, offering new cosmological scenarios and invalidating several paradoxes, while also introducing the challenge of explaining how islands of localized time may emerge and give rise to localized histories.
TIME AND THE UNIVERSE
The universe is not static, and changes continuously occur within it, unaffected by our existence.
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