ASTR 1514: CHAPTER 15 VOCABULARY
34 Cards in this Set
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Olbers' Paradox
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The conflict between observation and theory about why the night sky should or should not be dark.
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Static
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Unchanging overall.
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Unchanging overall.
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Astronomers and physicists who study cosmology.
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Astronomers and physicists who study cosmology.
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The study of the Universe as a whole.
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Observable Universe
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The part of the universe that you can see from your location in space and time.
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Expanding Universe
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The observed property of the universe that the average distance between galaxies is increasing with time.
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Big Bang
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The high-density, high-temperature state from which the expanding universe of galaxies began.
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Hubble Time
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One divided by the Hubble constant (H). The Hubble time is the age of the universe if it has expanded since the big bang at a constant rate.
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Cosmic Microwave Background Radiation
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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 2.7K.
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Antimatter
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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.
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Age
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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 into darkness.
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Reionization
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The stage in the early history of the universe when ultraviolet photons from the first stars ionized the gas filling space.
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Isotropy
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The assumption that, in its general properties, the universe look the same in every direction.
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Homogeneity
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The assumption that, on the large scale, matter is uniformly spread through the universe.
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Cosmological Principle
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The assumption that any observer in any galaxy sees the same general features of the universe.
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Closed Universe
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A model universe in which the average density is great enough to stop the expansion and make the universe contract.
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Flat Universe
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A model of the universe in which space-time is not curved.
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Open Universe
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A model of the universe which the average density is less than the critical density needed to halt the expansion.
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Critical Density
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The average density of the universe needed to make its curvature flat.
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Nonbaryonic Matter
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Proposed dark matter made up of particles other than protons and neutrons (baryons).
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WIMPs (Weakly Interacting Massive Particles)
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WIMPs (Weakly Interacting Massive Particles)
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Hot Dark Matter
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Dark matter made up of particles such as neutrinos, traveling at or nearly at the speed of light.
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Cold Dark Matter
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Mass in the universe, as yet undetected except for its gravitational influence, which is made up of slow-moving particles.
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Flatness Problem
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In cosmology, the peculiar circumstance that the early universe must have contained almost exactly the right amount of matter to make space-time flat.
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Horizon Problem
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In cosmology, the circumstance that the primordial background radiation seems much more isotropic than can be explained by the standard big bang theory.
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Inflationary Universe
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A version of the big bang theory, derived from grand unified theories, that includes a rapid expansion when the universe was very young.
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GUTs (Grand Unified Theories)
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Theories that attempt to unify (describe in a similar way) the electromagnetic, weak, and strong forces of nature.
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Cosmological Constant
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A constant in Einstein's equations of space and time that represents a force of repulsion.
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Quintessence
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The postulated energy that fills empty space and drives the acceleration of the universe.
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Dark Energy
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The energy believed to fill empty spaces and drive the acceleration of the expanding universe.
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Big Rip
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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.
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Large-Scale Structure
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The distribution of clusters and superclusters of galaxies in filaments and walls enclosing voids.
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Superclusters
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A cluster of galaxy clusters.
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Voids
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Extremely large structural feature in the universe, regions tens or hundreds of megaparsecs in size, containing few or no visible galaxies.
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ASTR 1514: CHAPTER 15 VOCABULARY