How do we know how big the universe is

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Understanding the Size of the Universe

Observable Universe and Cosmic Horizon

The size of the observable universe is often defined by the distance that light has traveled since the Big Bang. This distance, known as the cosmic horizon, is approximately 46 billion light-years. This horizon represents the furthest point from which light has had time to reach us since the beginning of the universe1.

Cosmic Microwave Background (CMB) and Topology

The topology of the universe can be studied through the cosmic microwave background (CMB) radiation. By searching for matching circles of temperature patterns in the CMB, scientists can infer the shape and size of the universe. Data from NASA's WMAP satellite has placed a lower bound on the size of the universe at 24 gigaparsecs (Gpc)2 3. This method helps rule out certain topological models, such as the Poincare dodecahedral space, suggesting that the universe is much larger than this lower bound.

General Relativity and Gravitational Field Equations

Using modified Einsteinian gravitational field equations, it is possible to calculate the size and age of the universe. These equations take into account the mass of the Earth and the cosmos, providing insights into the universe's mass density and gravitational properties. This approach allows for the determination of the universe's initial radius and mass, offering a theoretical framework for understanding its size4.

Hubble Constant and Density Measurements

The Hubble constant, which measures the rate of expansion of the universe, and the density of the universe are crucial for estimating the size of galaxies and the universe itself. Recent measurements have achieved better than 1% accuracy, significantly improving our understanding of the universe's scale compared to two decades ago5.

Multiverse Theories and Observable Patches

In cosmological models consistent with General Relativity, the universe's total volume can be finite or infinite, depending on its spatial curvature. Current data suggest a nearly flat curvature, allowing for a lower limit on the universe's volume. Based on WMAP data, there are at least 21 observable universe-sized patches, with the potential for many more beyond our observational capabilities7.

Photon Sphere and Event Horizon

A new model interprets the visible universe as being inside a photon sphere with a radius of 14.3 Gpc. This model suggests that the horizon distance of 14.0 Gpc is an arc rather than a straight line, due to photons following circular orbits. This interpretation aligns with observed cosmic microwave background (CMB) redshifts and the uniformity of the CMB, providing a coherent explanation for the universe's size and structure8.

Conclusion

The size of the universe is a complex and multifaceted topic, explored through various methods including the cosmic horizon, CMB analysis, gravitational field equations, and multiverse theories. While the observable universe is about 46 billion light-years in radius, the true extent of the universe remains a subject of ongoing research and discovery.

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Most relevant research papers on this topic

Is the universe infinite or just very big

The cosmic horizon is about 46 billion light-years, and it's a three-dimensional equivalent of the 2D-horizon people see on Earth.

2015·0citations·M. Campbell·New Scientist

New Scientist ··DOI

Extending the WMAP bound on the size of the Universe

The WMAP bound on the size of the Universe can be extended by optimally filtering the CMB radiation, excluding the suggestion that we live in a Poincare dodecahedral space.

2006·66citations·J. Key et al.·Physical Review D

Physical Review D ··DOI

Extending the WMAP bound on the size of the Universe

The WMAP bound on the universe's size can be extended by optimally filtering the CMB radiation, but the Poincare dodecahedral space hypothesis remains unconfirmed.

2007·55citations·Joey Shapiro Key et al.·Physical Review D

Physical Review D ··DOI

Determining the Size, Mass, Gravity and Density of the Present and Primordial Universe by Means of a Modified Einstein’s Gravitational Field Equation

The modified Einsteinian gravitational field equation can determine the size and age of the universe, with the primordial density being 4.29•1090 kgm-3 and the initial radius and mass being 1.5334•10-32m and 6.4877•10-5 kg, respectively.

Preprint

2016·1citation·T. Nagy·viXra

viXra ··DOI

The Weight, Shape, and Fate of the Universe

The Hubble constant and universe density have improved to within 1% accuracy, allowing us to estimate the size, luminosity, and mass of galaxies with greater precision.

2013·0citations·G. Rhee

·DOI

The Classification of Universes

This paper proposes a classification of universes, estimating the range of sizes supporting life as we know it, and suggests that theories of the multiverse may eventually be scientifically viable.

2004·17citations·J. Bjorken·Physical Review D

Physical Review D ··DOI

HOW MANY UNIVERSES DO THERE NEED TO BE

There are at least 21 universes with the same volume as ours, but we cannot know the number of observable universes beyond 105 patches.

2006·2citations·Douglas Scott et al.·International Journal of Modern Physics D

International Journal of Modern Physics D ··DOI

A New Interpretation of the Size of the Visible Universe and its Implications

The new model interprets the visible universe as the surface of a sphere with radius 4.46 0.06 Gpc, explaining the cosmic microwave background redshift and Type Ia supernovae redshifts without inflation theory.

2010·1citation·B. Vlahovic·Bulletin of the American Physical Society

Bulletin of the American Physical Society ··DOI

The Mass of the Universe

The mass of the universe is approximately 2.55 1049 tons, which is close to the weight of the universe calculated on the basis of stars.

1940·19citations·C. Beadnell·Nature

Nature ··DOI

THE SIZE OF THE UNIVERSE

Before we can discuss the size of the universe it is necessary to define exactly what we are talking about. Astronomers have in the past been somewhat loose in their use of the word "universe.'' About ten years ago one of the much-discussed topics of the day was the "theory of island universes" universes in the plural ! A universe in that discussion was what we now call a galactic system, a stellar system like our own. As I am using the word tonight, there is only one universe, which contains all these systems, and everything that can be observed and that we can think of as being observable, either now or in the future. The universe is the whole of all things that exist in the physical or outer world. The next question to be considered is : has the universe any size at all? This question, whether the universe is of finite size or infinite, has occupied the minds of some of the greatest of mankind ever since science was born. There exists a delightful little tract, written by Archimedes, the greatest of Greek mathematicians, about 200 b.c. It is called "On the Grains of Sand" and is cast in the form of a letter addressed to the king of Syracuse. It begins as follows : "There are those who think, King Gelo, that the number of grains of sand is infinite ; that is, the grains of sand not only in the environs of Syracuse and the rest of Sicily, but also in all parts of the world whether inhabited or uninhabited. Others think that it is not infinite, but that no number can be named so large that it would exceed the said number of grains of sand. It appears that those who think so would still less be able to imagine

1932·3citations·W. Sitter·Publications of the Astronomical Society of the Pacific

Publications of the Astronomical Society of the Pacific ··DOI

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