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33 Cards in this Set

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Matter composed of antiparticles, which upon colliding with a matching particle of normal matter annihilate and convert the mass of both particles into energy. The antiproton is the antiparticle of the proton, and the positron is the antiparticle of the electron. (p. 333)
big bang
The high-density, high-temperature state from which the expanding universe of galaxies began. (p. 329)
big rip
The fate of the universe if dark energy increases with time and galaxies, stars, and even atoms are eventually ripped apart by the accelerating expansion of the universe. (p. 346)
closed universe
A model universe in which the average density is great enough to stop the expansion and make the universe contract. (p. 339)
cosmic microwave background radiation
Radiation from the hot clouds of the big bang explosion. The large red shift makes it appear to come from a body whose temperature is only 2.7 K. (p. 333)
cosmological constant
A constant in Einstein's equations of space and time that represents a force of repulsion. (p. 345)
cosmological principle
The assumption that any observer in any galaxy sees the same general features of the universe. (p. 336)
The study of the nature, origin, and evolution of the universe. (p. 326)
critical density
The average density of the universe needed to make its curvature flat. (p. 337)
dark age
The period of time after the glow of the big bang faded into the infrared and before the birth of the first stars, during which the universe expanded in darkness. (p. 334)
dark energy
The energy believed to fill empty spaces and drive the accelration of the expanding universe. (p. 345)
flat universe
A model of the universe in which space-time is not curved. (p. 339)
flatness problem
In cosmology, the peculiar circumstance that the early universe must have contained almost exactly the right amount of matter to make space-time flat. (p. 343)
grand unified theories (GUTs)
Theories that attempt to unify (describe in a similar way) the electromagnetic, weak, and strong forces of nature. (p. 343)
See grand unified theories.
The assumption that, on the large scale, matter is uniformly spread through the universe. (p. 336)
horizon problem
In cosmology, the circumstance that the primordial background radiation seems much more isotropic than can be explained by the standard big bang theory. (p. 343)
hot dark matter
Dark matter made up of particles such as neutrinos traveling at or nearly at the speed of light. (p. 342)
Hubble time
The age of the universe, equivalent to 1 divided by the Hubble constant. The Hubble time is the age of the universe if it has expanded since the big bang at a constant rate. (p. 330)
inflationary universe
A version of the big bang theory that includes a rapid expansion when the universe was very young. Derived from grand unified theories. (p. 343)
The assumption that in its general properties the universe looks the same in every direction. (p. 336)
large-scale structure
The distribution of clusters and superclusters of galaxies in filaments and walls enclosing voids. (p. 346)
Massive compact halo objects. Low-luminosity objects such as planets and brown dwarfs that contribute to the mass of the halo. (p. 342)
nonbaryonic matter
Proposed dark matter made up of particles other than protons and neutrons (baryons). (p. 341)
observable universe
The part of the universe that we can see from our location in space and in time. (p. 328)
Olbers' paradox
The conflict between observation and theory about why the night sky should or should not be dark. (p. 326)
open universe
A model of the universe in which the average density is less than the critical density needed to halt the expansion. (p. 339)
oscillating universe theory
The theory that the universe begins with a big bang, expands, is slowed by its own gravity, and then falls back to create another big bang. (p. 340)
The postulated energy that fills empty space and drives the acceleration of the universe. (p. 345)
The stage within 300,000 years of the big bang, when the gas became transparent to radiation. (p. 334)
The stage in the early history of the universe when ultraviolet photons from the first stars ionized the gas filling space. (p. 334)
steady-state theory
The theory (now generally abandoned) that the universe does not evolve. (p. 333)
A cluster of galaxy clusters. (p. 346)