Cosmological Constant: A Brief Overview
The cosmological constant (Λ), introduced by Einstein in 1917, has evolved into the broader concept of Dark Energy. Accurate measurements from distant supernovae in 1998 revealed that the universe's expansion is accelerating, aligning with the existence of dark energy.
The Cosmological Constant Problem
The observed vacuum energy density (Λ) is significantly smaller than theoretical predictions. Raphael Bousso's comprehensive study ties this issue to the "vacuum landscape" of string theory, offering potential explanations via the multiverse concept, where different regions of space exhibit diverse properties.
Einstein’s “Greatest Mistake”
Originally proposed and later retracted by Einstein, the cosmological constant has gained renewed interest due to the accelerating universe's expansion, becoming a fundamental part of the standard cosmological model.
Quantum Field Theory and the Vacuum Energy Density
The contributions from various fields in the Standard Model result in a theoretical prediction for Λ that is orders of magnitude larger than observed. String theory posits multiple stable and metastable voids, each with unique physical constants, potentially leading to many universes with different laws and constants.
Multiverse Model and Eternal Inflation
The "multiverse" model allows regions with abnormally small cosmological constants to match our observations. Supported by void decay and “eternal inflation” dynamics, this model explains the continuous, exponential expansion, forming new universes with different Λ values.
String Theory and the View of the Multiverse
String theory, formulated in nine or ten spatial dimensions, suggests multiple ways to condense these dimensions, leading to numerous possible three-dimensional spaces. Bousso visualizes this as a potential function with multiple minima, each representing different vacuum states.
Bubble Universes and Eternal Inflation
In a universe starting with positive energy, transitions between different vacuum states can form bubble universes. This process results in eternal inflation, where new bubble universes, each with unique physical properties, continuously emerge.
The Coincidence Problem
Bousso's framework suggests that regions with small cosmological constants are necessary for the existence of observers. High cosmological constants do not support the complexity required for life.
Analogies for Better Understanding
Balloon Analogy: The universe's expansion is like a balloon. The actual small amount of energy results in slight expansion, similar to the small cosmological constant observed.
Lottery Analogy: Imagine a lottery with 10^500 tickets. Many tickets represent uninhabitable universes, but a few will have perfect conditions for life, like our universe.
Boiling Water Analogy: Each bubble in boiling water is like a new universe. Some bubbles last longer, like our universe in the vast, eternally boiling multiverse.
References
Bousso, R., & Polchinski, J. (2000). Quantization of Four-form Fluxes and Dynamical Neutralization of the Cosmological Constant. arXiv:hep-th/0004134.
Douglas, M. R. (2003). The Statistics of String/M Theory Vacua. arXiv:hep-th/0303194.
Susskind, L. (2003). The Anthropic Landscape of String Theory. arXiv:hep-th/0302219.
Kachru, S., Kallosh, R., Linde, A., & Trivedi, S. P. (2003). de Sitter Vacua in String Theory. arXiv:hep-th/0301240.
Weinberg, S. (1987). Anthropic Bound on the Cosmological Constant. Physical Review Letters, 59(23), 2607-2610.
doi:10.1103/PhysRevLett.59.2607.
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17 май 2024
