Observable universe
Introduction
The Observable universe is a vast cosmic region that can be seen from Earth or its space-based telescopes and sensors. It is a spherical volume of space centered on the observer, regardless of the shape of the universe as a whole. The word "observable" in this context does not refer to the capability of modern technology to detect light or other information from an object, but rather indicates that it is possible in principle for light or other signals from the object to reach an observer on Earth.
Size and Scale
The size of the observable universe is determined by the Cosmological horizon – the maximum distance from which particles could have traveled to the observer in the age of the universe. This boundary is estimated to be about 93 billion light years in diameter. However, this does not represent the actual size of the universe, which remains unknown and may be infinite.
Composition
The observable universe is composed primarily of Dark energy, Dark matter, and ordinary (baryonic) matter. Dark energy, a type of energy that permeates all of space, is the dominant form, making up about 68% of the universe's composition. Dark matter, which cannot be seen directly but can be inferred by its gravitational effects, makes up about 27%. The remaining 5% is ordinary matter, which includes stars, galaxies, and everything we can directly observe.
Structure
The large-scale structure of the observable universe is characterized by a hierarchical organization. At the largest scales, it is composed of a cosmic web of Galaxy clusters and superclusters, separated by vast voids. These structures are shaped by the gravitational attraction of dark matter and the expansion of the universe driven by dark energy.
Observation and Study
The study of the observable universe involves multiple disciplines within Astronomy and Cosmology. Observations of the cosmic microwave background radiation, the oldest light in the universe, have provided crucial insights into the universe's early history and composition. Meanwhile, the study of distant galaxies and their distribution has shed light on the universe's large-scale structure and evolution.
Limitations of Observation
Despite the vast size of the observable universe, there are limitations to our ability to observe it. Due to the universe's expansion, distant objects are receding from us faster than the speed of light, making them unobservable in principle. This phenomenon, known as the Cosmological horizon, sets a limit to the observable universe.
Future of the Observable Universe
The future of the observable universe is subject to ongoing research and debate. Current theories suggest that the universe's expansion, driven by dark energy, will continue to accelerate. This could lead to a future in which distant galaxies become unobservable, effectively shrinking the observable universe.