Astronomy Exam Review Cosmology Part 1 PDF

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Cosmology, Part 1: The Big Bang (Chapter 11: 11.1-11.2, Assignment 20) The Edge-Centre Problem • The universe has no edge and therefore no centre " • Cosmology - the study of the nature origin and evolution of the universe" Olbers’s Paradox • The conflict between theory and evidence regarding the darkness of the night sky" • Observable Universe – The part of the universe that you can see from your location in space and in time" Cosmic Expansion • In 1929, Edwin Hubble published his discovery that the sizes of galaxy redshifts are proportional to galaxy distances " • This suggests that the universe is expanding " The Big Bang • Astronomers can trace back in time to infer an initial high-density, high-temperature state, also referred to as the big bang " • Hubble Time –The age of the universe (approximately 14 billion years), equivalent to 1 divided by the Hubble constant " • The Hubble time is the age of the universe based on its expansion at a constant rate since the big bang " Evidence for the Big Bang • Cosmic Microwave Background (CMB) – Radiation from the hot matter of the universe soon after the big bang " • The Large Redshift makes it appear to come from a blackbody with a temperature of 2.7 K " The Big Bang • Antimatter – Matter composed of antiparticles, which upon colliding with a matching particle of normal matter, annihilates, converting the mass of both particles into energy" • Recombination–The stage when the gas became transparent to radiation " • 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 " • Reionization – The stage in the early history of the universe when ultraviolet photons from the first stars ionized the gas that filled space " Looking at the Universe • Isotropy–The observation that, in its general properties, the universe looks the same in every direction " • Homogeneity – The observation that, on the large scale, matter is uniformly spread through the universe " • Cosmological Principle – The assumption that any observer in any galaxy sees the same general features of the universe " Cosmic Redshift • General relativity explains that cosmic redshifts are caused by the stretching of photon wavelengths as they travel through expanding space-time " Model Universes • Open Universe – Space-time is curved in such a way that the universe is infinite "

• Closed Universe – Space-time is curved to meet itself, and the universe is finite " • Flat Universe – Space-time is not curved " • Critical Density – The average density of matter and energy in the universe needed to make its curvature flat "

Dark Matter in Cosmology • Regular matter is also called baryonic matter " • Non-baryonic Matter – Proposed dark matter made up of particles other than protons and neutrons (baryons)" • Cold Dark Matter – Dark matter that is made of slow-moving particles" Inflation • Flatness Problem–The circumstance that the primordial background radiation seems much more isotropic than can be explained by the standard big bang theory" • Horizon Problem – A version of the big bang theory that includes a rapid expansion when the universe was very young " • The inflationary big bang resolves both the flatness and the horizon problems " Dark Energy and Acceleration • Cosmological Constant – A constant in Einstein’s equations of space and time that represents a force of repulsion " • Quintessence – A possible form of dark energy that can change in strength as the universe ages " • Dark Energy – The energy believed to drive the acceleration of the expanding universe" The Fate of the Universe • The ultimate fate of the universe depends on the nature of dark energy " • If dark energy increases in strength with time, the universe expansion may end up in a big rip " Origin of Structure • Clusters appear to be grouped into superclusters, which are not randomly scattered " • They are distributed in long, narrow filaments and thin walls that outline great voids nearly empty of galaxies (large-scale structure) " • At the moment of inflation, tiny quantum mechanical fluctuations would have been stretched to become very large, but subtle, variations in gravitational fields, which could have later led to the formation of clusters, filaments, and walls " CMB Irregularities and the Curvature of Space-Time • The size of the irregularities in the cosmic background radiation show that the observations fit the flat universe model well " • The results from the WMAP and Planck observations indicate that:" • The universe is 13.8 billion years old" • The universe contains 5% baryonic matter, 27% dark matter, and 68% dark energy...