15 articles
Anthropic principle
The anthropic principle is a rule in cosmology stating that what we observe must be compatible with our existence as observers, introduced by Brandon Carter in 1973.
Big Bounce
The Big Bounce, also called the cosmic bounce, is a hypothetical cosmological model in which a contracting universe rebounds into expansion, replacing the big bang singularity.
Conformal cyclic cosmology
Conformal cyclic cosmology (CCC) is a cosmological model proposed by Roger Penrose in 2010, in which our universe is one aeon in an endless sequence of aeons.
Copernican principle
The Copernican principle is the foundational cosmological assumption that we are not preferred observers of the universe, named for Nicolaus Copernicus, whose 1543 heliocentrism displaced Earth from the center.
Dark flow
Dark flow is a disputed claim that galaxy clusters move together in a single direction, announced in 2008 from WMAP data, but Planck analyses found no detection.
Drake equation
The Drake equation, also called the Green Bank equation, is a 1961 formula by Frank Drake estimating the number of radio-transmitting civilizations in the Milky Way.
Fermi paradox
The Fermi paradox, also called the Fermi-Hart paradox, is the conflict between the expected abundance of alien civilizations and the total lack of evidence for them.
Fractal cosmology
Fractal cosmology is a family of proposals in physical cosmology that the galaxy distribution, or spacetime itself, is fractal; SDSS and WiggleZ surveys find homogeneity beyond roughly 70–100 megaparsecs.
Loop quantum cosmology
Loop quantum cosmology (LQC) applies loop quantum gravity to the early universe, replacing the big bang singularity with a quantum bounce; its predicted effects may leave imprints in the cosmic microwave background.
Modified Newtonian dynamics
Modified Newtonian dynamics (MOND), or Milgrom's law, is a proposed alternative to dark matter in which Newtonian mechanics breaks down at very low gravitational accelerations, proposed by Mordehai Milgrom in 1983.
Olbers' paradox
Olbers' paradox, also called the dark night sky paradox, asks why the night sky is dark if the universe is infinite, eternal, and full of stars.
Rare Earth hypothesis
The Rare Earth hypothesis, or Rare Earth theory, argues that complex extraterrestrial life is likely rare even if microbial life is common across the universe.
Space animal hypothesis
The space animal hypothesis proposes that some UFOs are living organisms native to Earth's atmosphere or space rather than spacecraft, first argued by John Philip Bessor in 1947.
Tired light
Tired light is a class of non-expanding cosmological models proposed by Fritz Zwicky in 1929, in which redshift comes from photons losing energy in transit rather than cosmic expansion.
Unidentified flying object
An unidentified flying object (UFO), also known as unidentified aerial phenomena (UAP), is any object or light in the sky that resists identification after investigation, often associated with alien spacecraft.