Does the universe have an edge
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Does the Universe Have an Edge?
Concept of the Universe's Edge in Cosmology
The question of whether the universe has an edge is a profound one that has intrigued scientists and philosophers alike. The concept of an "edge" in the universe can be interpreted in various ways, depending on the context and the theoretical framework being considered.
Hyperbolic Geometry and the Universe's Edge
One argument against the universe having an edge is rooted in hyperbolic geometry. This perspective suggests that as one approaches the supposed edge of the universe, both the observer and their measuring instruments would shrink in such a way that the edge would never be reached. This idea challenges the traditional notion of an edge as a physical boundary that can be approached and crossed1.
Cosmological Simulations and Galactic Edges
In the context of galactic structures, cosmological simulations have been used to define the "edge" of galaxies like the Milky Way. These simulations identify caustics, which are regions where there is a significant drop in density or radial velocity. For the Milky Way, two primary caustics are identified: the outermost caustic, known as the "splashback" radius, and a second caustic that marks the edge of virialized material. These caustics provide a measurable boundary for the galaxy, although they do not imply an edge to the universe itself2.
Einstein's Theory of Relativity and the Universe's Boundaries
Einstein's theory of relativity offers insights into the nature of space and time, suggesting that the universe is expanding from a Big Bang. This expansion implies that galaxies are moving away from each other, potentially beyond the edge of the visible universe. However, this does not necessarily mean that the universe has a physical edge; rather, it indicates that there are regions beyond our observational capabilities3.
Quantum Hall Systems and Expanding Edges
In quantum Hall systems, expanding edges can simulate 1+1 dimensional expanding universes. These systems allow for the study of phenomena such as Hawking radiation and entanglement behavior in a controlled environment. The expansion of the edge region in these systems can be likened to a de Sitter universe, providing a unique perspective on the concept of an edge in a quantum context4.
The Hartle-Hawking No-Boundary Proposal
The Hartle-Hawking no-boundary proposal suggests that the universe may have had an infinite period of inflation, implying that it does not have a traditional edge or singularity. According to this proposal, the universe's classical spacetime might have an edge or singularity at an infinite amount of comoving time in the past, but this does not translate to a finite proper time for geodesics with non-zero momentum. Thus, the universe could be infinitely old and still possess singularities5.
Conclusion
The question of whether the universe has an edge is complex and multifaceted. Various theoretical frameworks, from hyperbolic geometry to cosmological simulations and quantum models, offer different perspectives on this issue. While some theories suggest that the universe does not have a physical edge, others propose boundaries that are more abstract or related to observational limits. Ultimately, the nature of the universe's edge remains an open question in cosmology.
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The Edge of the Universe Noneuclidean Wallpaper
The universe could have an edge, and if matter shrinks, it could fit through the edge, making it part of the universe.
The edge of the Galaxy
The edge of the Milky Way halo is 292 61 kpc, with two caustics in dark matter and one in stars, and can be determined using radial density and radial velocity profiles.
Beyond Einstein: from the Big Bang to black holes
The Beyond Einstein program aims to answer three profound questions: what powered the Big Bang? what happens to space, time, and matter at the edge of a black hole? and what is the mysterious dark energy pulling the Universe apart?
Analog de Sitter universe in quantum Hall systems with an expanding edge
Expanding edges in quantum Hall systems simulate de Sitter universes, leading to Hawking radiation and entanglement death, which is related to quantum to classical transition in cosmic inflations.
Is the Universe infinitely old?
The universe may have had an infinite period of inflation, but the spacetime would still be singular even if infinitely old.
From the Edge of Time to the Infinite Future of the Universe. Paul Davies, What’s Eating the Universe? And Other Cosmic Questions, The University of Chicago Press, Chicago 2021, pp. 184
Paul Davies explores contemporary cosmology and philosophical issues, highlighting how age-old puzzles have been solved and new discoveries are upending our understanding of physical reality.
A Single Closed Theory of the Universe
When we speak of the universe, what do we mean? Today it is thought of as an entity of nearly infinite size and dimensions, approximately 13.7 billions of years old, full of perhaps trillions of stars organized into a countless number of galaxies. It is a universe composed of many parts. There is no center, no central point, and gazing in any direction from any point one would never see the edge.
The large-scale structure of the Universe
The rich tapestry of present-day cosmic structure arose during the first instants of creation, when weak ripples were imposed on the otherwise uniform and rapidly expanding primordial soup, and over 14 billion years, gravitational forces amplified these ripples to enormous proportions, producing ever-growing concentrations of dark matter in
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