Cosmology Explained: The Science of the Universe's Origin and Fate
The Big Bang, dark matter, dark energy, and the fate of the universe
Cosmology is the branch of astronomy concerned with the origin, structure, evolution, and eventual fate of the universe as a whole. The Big Bang theory — now confirmed by multiple lines of independent evidence including cosmic microwave background radiation, the expansion of the universe, and the abundance of light elements — describes a universe that began in an extremely hot, dense state approximately 13.8 billion years ago and has been expanding and cooling ever since.
Astronomy: Big Bang Nucleosynthesis
Big Bang Nucleosynthesis In physical cosmology, Big Bang nucleosynthesis (also known as primordial nucleosynthesis, and abbreviated as BBN) is a model for the production of light nuclei (including, but not limited to, 2H, 3He, 4He, and 7Li) during the first ~20 minutes of the evolution of the universe. The predictions of BBN rely on a combination of thermodynamic arguments and measurements of rat
Read commentary →Astronomy: Cosmic Inflation
Cosmic Inflation In physical cosmology, cosmic inflation, cosmological inflation, or just inflation, is a theory of exponential expansion of space in the very early universe. This enormous expansion supercooled the universe and ended when the energy content of the field driving inflation condensed into hot, dense particles, a process called reheating.
Read commentary →Astronomy: Cosmic Microwave Background
Cosmic Microwave Background The cosmic microwave background (CMB, CMBR), or relic radiation, is microwave radiation that fills all space in the observable universe. With a standard optical telescope, the background space between stars and galaxies is almost completely dark.
Read commentary →Astronomy: Cosmic Strings
Cosmic Strings Cosmic strings are hypothetical 1-dimensional topological defects which may have formed during a symmetry-breaking phase transition in the early universe when the topology of the vacuum manifold associated to this symmetry breaking was not simply connected. In less formal terms, they are hypothetical long, thin defects in the fabric of space.
Read commentary →Astronomy: Cosmic Voids
Cosmic Voids Cosmic voids (also known as dark space) are vast spaces between filaments (the largest-scale structures in the universe), which contain very few or no galaxies. In spite of their size, most galaxies are not located in voids but are gravitationally bound together, creating huge cosmic structures known as galaxy filaments.
Read commentary →Astronomy: Dark Energy
Dark Energy In physical cosmology and astronomy, dark energy is a proposed form of energy that affects the universe on its largest scales. Its primary effect is to drive the accelerating expansion of the universe.
Read commentary →Astronomy: Dark Matter
Dark Matter In astronomy and cosmology, dark matter is an invisible and hypothetical form of matter that does not interact with light or other electromagnetic radiation. Dark matter is implied by gravitational effects that cannot be explained by general relativity unless more matter is present than can be observed.
Read commentary →Astronomy: Gravitational Lensing
Gravitational Lensing A gravitational lens is matter, such as a cluster of galaxies or a point particle, that bends light from a distant source as it travels toward an observer. The amount of gravitational lensing is described by Albert Einstein's general theory of relativity.
Read commentary →Astronomy: Gravitational Waves
Gravitational Waves Gravitational waves are waves of spacetime curvature that propagate at the speed of light and are produced by the relative motion of gravitating masses. They were first predicted by Albert Einstein as a consequence of his general theory of relativity, appearing as "ripples in spacetime curvature".
Read commentary →Astronomy: Heat Death of the Universe
Heat Death of the Universe The heat death of the universe (also known as the Big Chill or the Big Freeze) is a scientific hypothesis regarding the ultimate fate of the universe which posits the universe will evolve to a state of no thermodynamic free energy and, having reached maximum entropy, will therefore be unable to sustain any further thermodynamic processes. Heat death does not imply any p
Read commentary →Astronomy: Large-Scale Structure
Large-Scale Structure The observable universe is a spherical region of the universe consisting of all matter that can be observed from Earth; the electromagnetic radiation from these astronomical objects has had time to reach the Solar System and Earth since the beginning of the cosmological expansion. The radius of this region is about 14.26 gigaparsecs (46.5 billion light-years or 4.40×1026 m).
Read commentary →Astronomy: Olbers' Paradox
Olbers' Paradox Olbers' paradox, also known as the dark night paradox or Olbers and Cheseaux's paradox, is a historical argument in astrophysics and physical cosmology that says the darkness of the night sky conflicts with the assumption of an infinite and eternal static universe. If the universe were static, homogeneous at a large scale, and populated by an infinite number of stars, any line of
Read commentary →Astronomy: Redshift
Redshift In physics, a redshift is an increase in the wavelength, or equivalently, a decrease in the frequency, of electromagnetic radiation (such as light). The opposite change, a decrease in wavelength and increase in frequency and energy, is known as a blueshift.
Read commentary →Astronomy: The Big Bang
The Big Bang The Big Bang is a physical theory that describes how the universe expanded from an initial state of high density and temperature. Various cosmological models based on the Big Bang concept explain a broad range of phenomena, including the abundance of light elements, the cosmic microwave background (CMB) radiation, the redshift of galaxies and the large-scale structure of the univers
Read commentary →Astronomy: The Big Crunch
The Big Crunch The Big Crunch is a hypothetical scenario for the ultimate fate of the universe, in which the expansion of the universe eventually reverses and the universe recollapses, ultimately causing the cosmic scale factor to reach absolute zero, an event potentially followed by a reformation of the universe starting with another Big Bang. The vast majority of valid evidence, however, indica
Read commentary →Astronomy: The Cosmic Web
The Cosmic Web The observable universe is a spherical region of the universe consisting of all matter that can be observed from Earth; the electromagnetic radiation from these astronomical objects has had time to reach the Solar System and Earth since the beginning of the cosmological expansion. The radius of this region is about 14.26 gigaparsecs (46.5 billion light-years or 4.40×1026 m).
Read commentary →Astronomy: The Drake Equation
The Drake Equation The Drake equation is a probabilistic argument used to estimate the number of active, communicative extraterrestrial civilizations in the Milky Way Galaxy. The equation was formulated in 1961 by Frank Drake, not for purposes of quantifying the number of civilizations, but as a way to stimulate scientific dialogue at the first scientific meeting on the search for extraterrestria
Read commentary →Astronomy: The Expanding Universe
The 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.
Read commentary →Astronomy: The Fermi Paradox
The Fermi Paradox The Fermi paradox is the discrepancy between the lack of conclusive evidence of advanced extraterrestrial life and the apparently high likelihood of its existence. In simple terms, the Fermi paradox asks why, given the vast number of stars and potentially habitable planets in our observable universe, there is no clear evidence of extraterrestrial civilizations.
Read commentary →Astronomy: The Great Attractor
The Great Attractor The Great Attractor is a region of gravitational attraction in intergalactic space and the apparent central gravitational point of the Laniakea Supercluster of galaxies that includes the Milky Way galaxy, as well as about 100,000 other galaxies. The observed attraction suggests a localized concentration of mass having the order of 1016 solar masses.
Read commentary →Astronomy: The Hubble Constant
The Hubble Constant Hubble's law, officially the Hubble–Lemaître law, is the observation in physical cosmology that galaxies are moving away from Earth at speeds proportional to their distance. In other words, the farther a galaxy is from the Earth, the faster it moves away.
Read commentary →Astronomy: The Multiverse Theory
The Multiverse Theory The multiverse is the hypothetical set of all universes. Together, these universes are presumed to comprise everything that exists: the entirety of space, time, matter, energy, information, and the physical laws and constants that describe them.
Read commentary →Astronomy: The Observable Universe
The Observable Universe The observable universe is a spherical region of the universe consisting of all matter that can be observed from Earth; the electromagnetic radiation from these astronomical objects has had time to reach the Solar System and Earth since the beginning of the cosmological expansion. The radius of this region is about 14.26 gigaparsecs (46.5 billion light-years or 4.40×1026 m
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What is the Big Bang theory in simple terms?
The Big Bang theory says the universe began about 13.8 billion years ago from an extraordinarily hot, dense state and has been expanding ever since. It does NOT describe an explosion in space — it describes space itself expanding. The evidence: all distant galaxies are moving away from us (Hubble, 1929), the universe has a uniform background radiation at -270°C (discovered 1965), and the ratio of hydrogen to helium throughout the universe matches what we would expect from that initial superhot state.