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