Expanding universe in the context of "Physical cosmology"

⭐ In the context of Physical Cosmology, the acceptance of the Big Bang theory as the leading cosmological model was most directly enabled by which combination of discoveries and theoretical frameworks?

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⭐ Core Definition: Expanding universe

The expansion of the universe is the increase in distance between gravitationally unbound parts of the observable universe with time. It is an intrinsic expansion, so it does not mean that the universe expands into anything or that space exists outside it. To any observer in the universe, it appears that all but the nearest galaxies (which are bound to each other by gravity) move away at speeds that are proportional to their distance from the observer, on average. While objects cannot move faster than light, this limitation applies only with respect to local reference frames and does not limit the recession rates of cosmologically distant objects.

The expansion of the universe was discovered by separate theoretical and observational work in the 1920s. Since then, the expansion has become a core aspect of the astrophysical field of cosmology. Many major scientific projects have sought to characterize the expansion and understand its effects.

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👉 Expanding universe in the context of Physical cosmology

Physical cosmology is a branch of cosmology concerned with the study of cosmological models. A cosmological model, or simply cosmology, provides a description of the largest-scale structures and dynamics of the universe and allows study of fundamental questions about its origin, structure, evolution, and ultimate fate. Cosmology as a science originated with the Copernican principle, which implies that celestial bodies obey identical physical laws to those on Earth, and Newtonian mechanics, which first allowed those physical laws to be understood.

Physical cosmology, as it is now understood, began in 1915 with the development of Albert Einstein's general theory of relativity, followed by major observational discoveries in the 1920s: first, Edwin Hubble discovered that the universe contains a huge number of external galaxies beyond the Milky Way; then, work by Vesto Slipher and others showed that the universe is expanding. These advances made it possible to speculate about the origin of the universe, and allowed the establishment of the Big Bang theory, by Georges Lemaître, as the leading cosmological model. A few researchers still advocate a handful of alternative cosmologies; however, most cosmologists agree that the Big Bang theory best explains the observations.

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Expanding universe in the context of Astronomical distance

Distance measures are used in physical cosmology to generalize the concept of distance between two objects or events in an expanding universe. They may be used to tie some observable quantity (such as the luminosity of a distant quasar, the redshift of a distant galaxy, or the angular size of the acoustic peaks in the cosmic microwave background (CMB) power spectrum) to another quantity that is not directly observable, but is more convenient for calculations (such as the comoving coordinates of the quasar, galaxy, etc.). The distance measures discussed here all reduce to the common notion of Euclidean distance at low redshift.

In accord with our present understanding of cosmology, these measures are calculated within the context of general relativity, where the Friedmann–Lemaître–Robertson–Walker solution is used to describe the universe.

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Expanding universe in the context of Steady state universe

In cosmology, the steady-state model or steady-state theory was an alternative to the Big Bang theory. In the steady-state model, the density of matter in the expanding universe remains unchanged due to a continuous creation of matter, thus adhering to the perfect cosmological principle, a principle that says that the observable universe is always the same at any time and any place. A static universe, where space is not expanding, also obeys the perfect cosmological principle, but it cannot explain astronomical observations consistent with expansion of space.

From the 1940s to the 1960s, the astrophysical community was divided between supporters of the Big Bang theory and supporters of the steady-state theory. The steady-state model is now rejected by most cosmologists, astrophysicists, and astronomers.The observational evidence points to a hot Big Bang cosmology with a finite age of the universe, which the steady-state model does not predict.

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Expanding universe in the context of Alexander Friedmann

Alexander Alexandrovich Friedmann (also spelled Friedman or Fridman; /ˈfriːdmən/; Russian: Алекса́ндр Алекса́ндрович Фри́дман; June 16 [O.S. June 4] 1888 – September 16, 1925) was a Russian and Soviet physicist and mathematician. He originated the pioneering theory that the universe is expanding, governed by a set of equations he developed known as the Friedmann equations.

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LINKED FROM (PARENTS)
← Physical cosmology ← Cosmological model ← Astronomical distance ← Steady state universe ← Alexander Friedmann ← Steady state theory ← Distance measures (cosmology) ← Steady-state model
LINKS TO (CHILDREN)
Big Bang → Proper length → Gravitational binding energy → Observable universe → Intrinsic and extrinsic properties (philosophy) → Hubble's law → Faster-than-light → Principle of locality → Reference frame → Astrophysics → Cosmology →