Universe definition science
Pro Research Analysisby 
Searched over 200M research papers
Understanding the Definition of the Universe in Science
Definition of the Universe in Cosmology
In cosmology, the universe is often defined as the contents of a spacetime box with comoving walls, large enough to contain measurable phenomena but not excessively larger. This definition allows for the construction of a local ensemble of universes, assuming that similar universes can be constructed further out with different standard model parameters, which are strongly correlated with the size of the universe, particularly the Hubble scale at late times. This approach helps in understanding the hierarchy problems of particle physics and suggests that theories of the multiverse may eventually be considered scientific.
The Big Bang and Cosmological Models
The Big Bang paradigm and the ΛCDM (Lambda Cold Dark Matter) model are central to modern cosmology but face challenges in empirical validation. These models involve concepts such as the emanation of the universe from a non-physical stage, cosmic inflation, and dark matter, which are difficult to test empirically. A more well-founded cosmology suggests that energy is conserved, the universe is persistent, and the 'perfect cosmological principle' holds, where waves and field perturbations expand exponentially with distance due to gravitation. This model also explains galaxy rotation curves through Modified Newtonian Dynamics (MOND).
Multiverse and Universe Classification
The concept of a multiverse assumes the existence of multiple universes, each with potentially different physical constants and properties. A standardized definition for member universes similar to our own involves the asymptotic value of the inverse Hubble constant at large times, with the cosmological constant playing a central role. This definition implies that the vacuum parameters and coupling constants of the standard model depend on the size of the universe, with anthropic considerations limiting the size of habitable universes to within a factor of two of our own.
Philosophical and Mathematical Perspectives
Philosophically, the term "universe" is derived from the Latin words "unus" (one) and "versus" (turned), meaning "turned into one". This implies that the universe encompasses all created things as one system, contrasting with chaos. Mathematically, the concept of a universe has been present in various forms, such as Grothendieck universes, which are used in many mathematical theories and are essential for constructing sets outside the considered universe. These definitions help in understanding the properties of non-empty universes and the construction of a tower of universes indexed by ordinal numbers.
Conclusion
The definition of the universe in science is multifaceted, encompassing cosmological, philosophical, and mathematical perspectives. In cosmology, it involves the contents of a spacetime box with comoving walls, while in the context of the multiverse, it includes universes with varying physical constants. Philosophically, it represents all created things as one system, and mathematically, it includes concepts like Grothendieck universes. These diverse definitions and models help in understanding the vast and complex nature of the universe.
Sources and full results
Most relevant research papers on this topic