Event that cosmologists consider the beginning of the universe, in which all matter and radiation in the entire universe came into being.
What is the Big Bang?
100
Quantity originally introduced by Einstein into general relativity to make his equations describe a static universe.
What is cosmological constant?
100
Generic name given to the unknown cosmic force field thought to be responsible for the observed acceleration of the Hubble expansion.
What is dark energy?
100
Geometry that the universe as a whole would have if the density of matter is above the critical value.
What is a closed universe?
100
Two assumptions that make up the basis of cosmology, namely that the universe is homogenous and isotropic on sufficiently large scales.
What is cosmological principle?
200
Assumed property of the universe such as the number of galaxies in an imaginary large cube of the universe is the same no matter where in the universe the cube is placed.
What is homogenity?
200
Geometry that the universe would have if the density of matter were less than the critical value.
What is an open universe?
200
The cosmic density corresponding to the dividing line between a universe that recollapses and one that expands forever.
What is critical density?
200
The study of the structure and evolution of the entire universe.
What is cosmology?
200
The almost perfect isotropic radio signal that is the electromagnetic remnant of the Big Bang.
What is the cosmic microwave background?
300
Assumed property of the universe such that the universe looks the same in every direction.
What is isotropic?
300
Short period of unchecked cosmic expansion early in the history of the universe.
What is inflation?
300
A universe in which the density of matter exceeds the density of radiation.
What is a matter-dominated universe?
300
A thought experiment suggesting that if the universe were homogenous, infinite, and unchanging, the entire night sky would be as bright as the surface of the sun.
What is Olber's Paradox?
300
Class of theories describing the behavior of the single force that results from unification of the strong, weak, and electromagnetic forces in the early universe.
What is Grand Unified Theories?
400
The production of elements heavier than hydrogen by nuclear fusion in the high temperatures and densities that existed in the early universe.
What is primordial nucleosynthesis?
400
Event in the early universe when atoms first formed, after which photons could propagate freely through space.
What is decoupling?
400
One of two conceptual problems with the standard Big Bang model, which is that there is no natural way to explain why the density of the universe is so close to the critical density.
What is the flatness problem?
400
One of two conceptual problems with the standard Big Bang model, which is that some regions of the universe that have very similar properties are too far apart to have exchanged information within the age of the universe.
What is the horizon problem?
400
Universe in which the density of matter is exactly equal to the critical density.
What is critical universe?
500
Early epoch in the universe, when the equivalent density of radiation in the cosmos exceeded the density of matter.