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  2. Shape of the universe - Wikipedia

    en.wikipedia.org/wiki/Shape_of_the_universe

    Global geometry: This pertains to the universe's overall shape and structure. The observable universe (of a given current observer) is a roughly spherical region extending about 46 billion light-years in all directions (from that observer, the observer being the current Earth, unless specified otherwise). [3]

  3. Universe - Wikipedia

    en.wikipedia.org/wiki/Universe

    The physical universe is defined as all of space and time [a] (collectively referred to as spacetime) and their contents. [10] Such contents comprise all of energy in its various forms, including electromagnetic radiation and matter, and therefore planets, moons, stars, galaxies, and the contents of intergalactic space.

  4. List of largest cosmic structures - Wikipedia

    en.wikipedia.org/wiki/List_of_largest_cosmic...

    Discovered through gamma-ray burst mapping. Largest-known regular formation in the observable universe. [8] Huge-LQG (2012–2013) 4,000,000,000 [9] [10] [11] Decoupling of 73 quasars. Largest-known large quasar group and the first structure found to exceed 3 billion light-years. "The Giant Arc" (2021) 3,300,000,000 [12] Located 9.2 billion ...

  5. Observable universe - Wikipedia

    en.wikipedia.org/wiki/Observable_universe

    The observable universe is a spherical region of the universe consisting of all matter that can be observed from Earth or its space-based telescopes and exploratory probes at the present time; the electromagnetic radiation from these objects has had time to reach the Solar System and Earth since the beginning of the cosmological expansion.

  6. Friedmann equations - Wikipedia

    en.wikipedia.org/wiki/Friedmann_equations

    This term originally was used as a means to determine the spatial geometry of the universe, where ρ c is the critical density for which the spatial geometry is flat (or Euclidean). Assuming a zero vacuum energy density, if Ω is larger than unity, the space sections of the universe are closed; the universe will eventually stop expanding, then ...

  7. Timeline of cosmological theories - Wikipedia

    en.wikipedia.org/wiki/Timeline_of_cosmological...

    c. 16th century BCE – Mesopotamian cosmology has a flat, circular Earth enclosed in a cosmic ocean. [1]c. 15th–11th century BCE – The Rigveda of Hinduism has some cosmological hymns, particularly in the late book 10, notably the Nasadiya Sukta which describes the origin of the universe, originating from the monistic Hiranyagarbha or "Golden Egg".

  8. Flatness problem - Wikipedia

    en.wikipedia.org/wiki/Flatness_problem

    The local geometry of the universe is determined by whether the relative density Ω is less than, equal to or greater than 1. From top to bottom: a spherical universe with greater than critical density (Ω>1, k>0); a hyperbolic, underdense universe (Ω<1, k<0); and a flat universe with exactly the critical density (Ω=1, k=0).

  9. Celestial spheres - Wikipedia

    en.wikipedia.org/wiki/Celestial_spheres

    In Greek antiquity the ideas of celestial spheres and rings first appeared in the cosmology of Anaximander in the early 6th century BC. [7] In his cosmology both the Sun and Moon are circular open vents in tubular rings of fire enclosed in tubes of condensed air; these rings constitute the rims of rotating chariot-like wheels pivoting on the Earth at their centre.