Definition of universe in cosmology
Pro Research Analysisby 
Searched over 200M research papers
Definition of Universe in Cosmology
Universe as a Physical and Observable Entity
In cosmology, the universe is typically defined as the largest set of physical objects that are causally connected to each other and to the region of spacetime accessible to us through astronomical observation. This means the universe includes everything that can, in principle, influence or be influenced by us, forming a maximal set of causally linked entities and regions .
Observable Universe vs. Entire Cosmos
Cosmologists often distinguish between the "observable universe"—the part we can see or measure—and the entire universe, which may extend far beyond what is observable. The observable universe is only a fraction of the whole cosmos, and our scientific models are based on the assumption that the laws of physics and the properties we observe locally are representative of the universe as a whole 35. However, the universe as a whole remains empirically inaccessible, and our understanding of its global properties is ultimately limited by what we can observe .
Universe as a Physical System and Philosophical Considerations
In standard physical cosmology, the universe is modeled as a physical system, allowing scientists to define and study its global properties, such as its geometry, expansion, and composition. However, there are philosophical debates about whether the universe can truly be considered a physical object in the same way as smaller systems, since we cannot observe or experiment with it as a whole. Some interpretations argue that the universe's global properties are under-determined and depend on philosophical preferences, making a strictly realist interpretation problematic .
Homogeneity, Isotropy, and the Cosmological Principle
A key assumption in cosmology is the cosmological principle, which states that the universe is homogeneous and isotropic on large scales. This means that, when viewed at a sufficiently large scale, the universe looks the same in every direction and at every location. This principle underpins the standard models of cosmology and allows scientists to use mathematical frameworks, such as the Friedmann-Lemaître-Robertson-Walker (FLRW) metric, to describe the universe's structure and evolution 5910.
Mathematical and Physical Descriptions
Cosmology uses mathematical models to describe the universe's geometry, expansion, and content. These models incorporate observations of cosmic microwave background radiation, galaxy distributions, and other large-scale structures to infer properties like the universe's age, shape (flat, open, or closed), and composition (including dark matter and dark energy) 79. The universe is often described as a dynamic, evolving system governed by physical laws that apply everywhere within it 47.
Conclusion
In summary, the universe in cosmology is defined as the totality of causally connected physical entities and regions, with scientific study focused on the observable part. While mathematical models and physical laws provide a framework for understanding its structure and evolution, philosophical questions remain about the nature and limits of our knowledge, especially regarding the universe as a whole beyond what we can observe 1235+2 MORE.
Sources and full results
Most relevant research papers on this topic
The cosmological model of universe: A review
The cosmological model explains the universe's expansion using general relativity, overcoming the shortcomings of the Newtonian theory and providing a basic understanding of the universe's geometry and expansion.
DOI