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Astronomy 2e

Key Terms

Astronomy 2eKey Terms

Key Terms

anthropic principle
idea that physical laws must be the way they are because otherwise we could not be here to measure them
Big Bang
the theory of cosmology in which the expansion of the universe began with a primeval explosion (of space, time, matter, and energy)
closed universe
a model in which the universe expands from a Big Bang, stops, and then contracts to a big crunch
cosmic microwave background (CMB)
microwave radiation coming from all directions that is the redshifted afterglow of the Big Bang
cosmological constant
the term in the equations of general relativity that represents a repulsive force in the universe
cosmology
the study of the organization and evolution of the universe
critical density
in cosmology, the density that is just sufficient to bring the expansion of the universe to a stop after infinite time
dark energy
the energy that is causing the expansion of the universe to accelerate; its existence is inferred from observations of distant supernovae
dark matter
nonluminous material, whose nature we don’t yet understand, but whose presence can be inferred because of its gravitational influence on luminous matter
deuterium
a form of hydrogen in which the nucleus of each atom consists of one proton and one neutron
flat universe
a model of the universe that has a critical density and in which the geometry of the universe is flat, like a sheet of paper
fusion
the building of heavier atomic nuclei from lighter ones
grand unified theories
(GUTs) physical theories that attempt to describe the four forces of nature as different manifestations of a single force
inflationary universe
a theory of cosmology in which the universe is assumed to have undergone a phase of very rapid expansion when the universe was about 10–35 second old; after this period of rapid expansion, the standard Big Bang and inflationary models are identical
lithium
the third element in the periodic table; lithium nuclei with three protons and four neutrons were manufactured during the first few minutes of the expansion of the universe
multiverse
the speculative idea that our universe is just one of many universes, each with its own set of physical laws
open universe
a model in which the density of the universe is not high enough to bring the expansion of the universe to a halt
photon decoupling time
when radiation began to stream freely through the universe without interacting with matter
weakly interacting massive particles
(WIMPs) weakly interacting massive particles are one of the candidates for the composition of dark matter
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