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The Big Bang is a physical theory that describes how the universe expanded from an initial state of high density and temperature. [1] The notion of an expanding universe was first scientifically originated by physicist Alexander Friedmann in 1922 with the mathematical derivation of the Friedmann equations.
As the universe expands and the matter in it thins, the gravitational attraction decreases (since it is proportional to the density), while the cosmological repulsion increases. Thus, the ultimate fate of the ΛCDM universe is a near-vacuum expanding at an ever-increasing rate under the influence of the cosmological constant.
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.
Lyra (Latin for 'lyre', from Ancient Greek: λύρα; pronounced: / ˈ l aɪ r ə / LY-rə) [2] is a small constellation.It is one of the 48 listed by the 2nd century astronomer Ptolemy, and is one of the modern 88 constellations recognized by the International Astronomical Union.
The Commentariolus (Little Commentary) is Nicolaus Copernicus's brief outline of an early version of his revolutionary heliocentric theory of the universe. [1] After further long development of his theory, Copernicus published the mature version in 1543 in his landmark work, De revolutionibus orbium coelestium (On the Revolutions of the Heavenly Spheres).
The earliest reference to the word "lyre" is the Mycenaean Greek ru-ra-ta-e, meaning "lyrists" and written in the Linear B script. [5] In classical Greek, the word "lyre" could either refer specifically to an amateur instrument, which is a smaller version of the professional cithara and eastern-Aegean barbiton, or "lyre" can refer generally to all three instruments as a family. [6]
The basic definition of Cosmology is the science of the origin and development of the universe. In modern astronomy, the Big Bang theory is the dominant postulation. Philosophy of cosmology is an expanding discipline, directed to the conceptual foundations of cosmology and the philosophical contemplation of the universe as a totality.
The initial state that Lemaître proposed for the Universe in his 1927 paper was Einstein's model of a static universe with a cosmological constant. [19] Also in 1927, Lemaître returned to MIT to defend his doctoral dissertation on The gravitational field in a fluid sphere of uniform invariant density according to the theory of relativity. [20]