Size observable universe

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The Size of the Observable Universe

Introduction to the Observable Universe

The observable universe encompasses all matter and energy that can be observed from Earth at the present time. This boundary is defined by the distance that light has traveled since the Big Bang, approximately 13.8 billion years ago. Due to the expansion of space, this distance is much larger than 13.8 billion light-years.

Calculating the Observable Universe's Size

Expansion and Cosmic Horizon

The size of the observable universe is determined by the cosmic horizon, which is the maximum distance from which light emitted since the Big Bang could have traveled to an observer on Earth. This distance is approximately 46 billion light-years, considering the expansion of the universe . The expansion of space means that objects currently at the edge of the observable universe were much closer when they emitted the light we now see.

Updated Measurements and Refinements

Recent studies have refined the measurements of the observable universe's size using updated cosmological parameters. For instance, data from the Planck satellite has provided more accurate values for these parameters, leading to a revised estimate of the observable universe's radius, which is 0.7% smaller than previous estimates . This refinement underscores the importance of continuous observation and data collection in cosmology.

Large-Scale Structures and Homogeneity

Homogeneity and Isotropy

The cosmological principle posits that the universe is homogeneous and isotropic on large scales. However, observations reveal complex structures even on these scales. For example, a giant ring-like structure with a diameter of 1720 Mpc has been discovered, challenging the notion of a homogeneous and isotropic universe . Such findings suggest that while the universe appears uniform on the largest scales, significant inhomogeneities exist.

Cell of Uniformity

The concept of the cell of uniformity helps describe the distribution of matter in the universe. This cell is estimated to be around 190 Mpc in size, within which the universe is filled with inhomogeneously distributed structures like galaxies and clusters . This approach aids in understanding the dynamics of these structures and their impact on the overall cosmological model.

Finite or Infinite Universe?

Theoretical Considerations

The question of whether the universe is finite or infinite has long intrigued scientists. If the universe is finite, it might be wrapped into a compact space, such as a hypertorus. Studies suggest that if this were the case, the fundamental domain must be at least 0.4 times the diameter of the observable universe . This implies that even if the universe is finite, it is still incredibly vast.

Observability and Boundaries

The size of the universe is observable in principle if it is multiply connected, meaning that certain boundary conditions could alter the detected spectrum of an accelerating monopole detector . This theoretical framework provides a method to potentially observe the finite nature of the universe.

Conclusion

The observable universe is a vast expanse, approximately 46 billion light-years in radius, shaped by the expansion of space and the finite age of the cosmos. While the universe appears homogeneous and isotropic on the largest scales, significant structures challenge this notion. Continuous advancements in observational technology and theoretical models are crucial for refining our understanding of the universe's size and structure. Whether the universe is finite or infinite remains an open question, but current observations and models provide a robust framework for exploring this profound mystery.

Sources and full results

Most relevant research papers on this topic

Large-scale structure observables in general relativity

This paper reviews key observables of the large-scale structure of the Universe, including redshift perturbation, distortion of cosmic rulers, and observed number density of tracers, in a general relativistic context.

2014·

34citations

·D. Jeong et al.

Size of the Observable Universe

The observable universe has a radius 0.7% smaller than previously estimated, due to the expansion of space and the finite age of the cosmos.

2016·

11citations

·Paul Halpern et al.

Is the Universe infinite or is it just really big

The fundamental domain of the universe must be at least 0.4 times the diameter of the observable universe, limiting compact cosmologies based on hexagonal prisms.

1998·

42citations

·Janna Levin et al.

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

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 aril 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·

0citations

·W. de Sitter

A giant ring-like structure at 0.78

The largest regular formation in the observable Universe, a 1720 Mpc ring-like structure, challenges the cosmological principle and is likely caused by a shell projection onto the sky.

2015·

46citations

·L. Balázs et al.

Observability of the size of the universe

The size of the universe can be observable in principle if our universe is multiple connected, as the spectrum detected by an accelerating monopole detector is altered by a periodic boundary condition.

1989·

1citation

·O. Abe

Remarks on mechanical approach to observable Universe

The mechanical approach is the most appropriate method to describe the dynamics of inhomogeneities in the observable Universe, allowing for a comparison of different cosmological models and highlighting potential problems with spatially flat models.

2013·

37citations

·M. Eingorn et al.

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

The Hubble constant and the expansion age of the Universe

Recent progress in measuring the Hubble constant suggests the Universe has a kinematic age of less than 142 billion years, favoring a low-matter-density universe and either an open or flat universe with a non-zero cosmological constant.

1999·

48citations

·Wendy L. Freedman

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