A105 024 Cosmo

Information about A105 024 Cosmo

Published on October 16, 2007

Author: Janelle

Source: authorstream.com

Content

A105 Stars and Galaxies:  A105 Stars and Galaxies Last units: 81, 82, 83, 84 Complete Nov. 21 NQ by TONIGHT FINAL NQ AVAILABLE WEDS MORNING, ONLINE LAST(!) homework due Thursday Projects due THURSDAY Today’s APOD Announcements…:  Announcements… SOLAR LAB Wednesday @2 PM The BIG BANG Theory:  The BIG BANG Theory What is the Big Bang Theory? Overview… The Universe began at a certain point in time The Universe began in a hot, dense state The Universe is expanding The Universe is evolving The Universe is cooling as it expands What evidence leads us to the Big Bang Theory? Olber’s Paradox The Expansion of the Universe The Cosmic Microwave Background The Helium Abundance Olber’s Paradox:  Olber’s Paradox You are lost in a very large forest The forest is uniformly dense with trees What do you see? Why Is the Sky Dark?:  Why Is the Sky Dark? IF: The universe is infinite The universe is filled with galaxies, clusters of galaxies, and superclusters The universe is eternal and unchanging Slide6:  Olbers’ Paradox If universe were 1) infinite 2) unchanging 3) everywhere the same Then, stars would cover the night sky everywhere The Resolution of Olber’s Paradox:  The Resolution of Olber’s Paradox The Universe has a finite age (about 14 billion years We can only see objects that are less than 14 billion light years from us Only those objects are close enough that their light has had time to travel to us This solution was first proposed by Poe in 1848 The Universe cannot be infinitely old. The Expansion of the Universe:  The Expansion of the Universe The spectral lines of galaxies are redshifted - galaxies are moving away from us. The velocity of recession depends on the distance to the galaxy: the farther away a galaxy is, the faster it recedes from us! Hubble’s Law:  Hubble’s Law The correlation discovered by Hubble was reported in 1929 as the formula: Velocity of Recession = Ho x Distance Ho is now know as the Hubble constant, and is measured in kilometers per second per megaparsec The Hubble constant gives us the age of the Universe:  The Hubble constant gives us the age of the Universe Velocity X Time (age) = Distance Age = Distance/Velocity Velocity = 45,000 km/sec Distance = 700 Mpc x 3x1019 km/Mpc Age = (2 x 1022 km) / (4.5 x 104) km/sec = 0.4 x 1018 seconds = 1.3 x 1010 years More Evidence for the Big Bang:  More Evidence for the Big Bang The cosmic microwave background radiation In 1965, two engineers at AT&T’s Bell Labs in New Jersey were puzzled by a constant “noise” in a microwave antenna they were calibrating Slide12:  The cosmic microwave background – the radiation left over from the Big Bang – was detected by Penzias & Wilson in 1965 A Serendipitous Discovery and a Nobel Prize:  A Serendipitous Discovery and a Nobel Prize The noise could not be explained by terrestrial or extraterrestrial sources. It seemed to be everywhere Penzias and Wilson shared the 1978 Nobel Prize in physics for their discovery of the Cosmic Microwave Background (CMB) radiation A uniform, faint signal from all over the sky The CMB:  The CMB In 1989, NASA launched the Cosmic Background Explorer (COBE) satellite to study the spectrum of the CMB COBE showed that the CMB has a perfect thermal spectrum at a temperature of 2.726 K Cold! No natural object in the Universe can be colder than this (why not?) Spectrum of a 2.726 K degree blackbody COBE data points The existence of the CMB shows that the universe was hot and dense in the distant past Wilkinson MICROWAVE Anisotropy Probe:  Wilkinson MICROWAVE Anisotropy Probe The microwave light that we detect has been stretched out as the universe has expanded, so light that was once very short wavelength is now reaching us as microwaves. Slide16:  The expansion of universe has stretched the wavelength of thermal radiation from the early universe to ~1000 times longer wavelength: visible/IR light has become microwave light Background has perfect thermal radiation spectrum at temperature 2.73 Kelvin… COLD! Wilkinson Microwave Anisotropy Probe:  Wilkinson Microwave Anisotropy Probe The microwave light captured in this picture is from 380,000 years after the Big Bang, over 13 billion years ago WMAP, a later NASA mission, shows us the beginning of cosmic structure in the Universe. Structure began as tiny temperature differences from place to place. The temperature differences WMAP sees vary by only millionths of a degree. A baby picture of the Universe:  A baby picture of the Universe Imagine a temperature map of the Earth in June 1992 WMAP makes a similar map of the sky What are we seeing in the baby picture?:  What are we seeing in the baby picture? The microwave radiation comes from the time when the temperature of the Universe became low enough for atoms to form (about 3000K) Matter became transparent, allowing light to travel great distances It is like seeing the bottom layer of clouds on an overcast day. Slide20:  Background radiation from Big Bang has been freely streaming across universe since atoms formed at temperature ~ 3,000 K: visible/IR Background Radiation More evidence for the Big Bang: The Helium Fraction:  More evidence for the Big Bang: The Helium Fraction The amount of helium compared to hydrogen formed as hot, primordial energy cools and forms into matter can be predicted by physical laws The fraction of helium in the Universe can be measured with observations The observed abundances of elements support the predictions of the Big Bang theory Slide22:  In the hot early universe, protons and neutrons combined to make long-lasting helium nuclei when universe was ~ 3 minutes old Nuclear physics shows us how to predict the amounts of hydrogen and helium that will be produced Slide23:  Big Bang theory prediction: 75% H, 25% He (by mass) Matches observations of nearly primordial gases Abundances of other light elements agree with Big Bang model having 4.4% normal matter:  Abundances of other light elements agree with Big Bang model having 4.4% normal matter The abundances depend on the density of the Universe when nuclei first formed Deuterium Helium-4 Helium-3 Lithium-7 Conclusion: The “Big Bang”:  Conclusion: The “Big Bang” Expansion implies a beginning, assuming that the universe has been expanding since it came into being Scientists call the beginning of our universe the Big Bang. The term was coined by British astronomer Sir Fred Hoyle in the 1940s (on a BBC broadcast!) The Big Bang represents a hot, dense primordial state of high energy (but not an explosion) Summary – Strong evidence supports the Big Bang Theory:  Summary – Strong evidence supports the Big Bang Theory The Universe is expanding (and cooling) from an initial, dense state Radiation left over from the Big Bang is now detected in the form of microwaves—the cosmic microwave background—which we can observe with a radio telescope Observations of helium and other light elements agree with the predictions for fusion in the Big Bang theory The Future?:  The Future? The universe is expanding, but the expansion should slow due to the gravitational attraction of all the matter in the Universe Will it continue to expand OR will the expansion slow down and reverse due to gravity? Does the expansion exceed the “escape velocity” of the universe? Will the Universe Keep Expanding Or Re-Collapse????:  it depends on the density of the Universe The critical density in the current epoch is 10-29 g/cm3, about one hydrogen atom per cubic meter About 25 times more than the observed mass of stars and gas But what about dark matter? there isn’t quite enough to re-collapse the Universe Will the Universe Keep Expanding Or Re-Collapse???? But the universe isn’t even slowing down…. Coping with a misconception…:  Coping with a misconception… If the Universe is expanding, what it is expanding into???????? NOTHING!!!! All of space came into being at the moment of the Big Bang. Space itself is expanding Balloon Model What aspects of the universe were unexplained with the first Big Bang theory?:  What aspects of the universe were unexplained with the first Big Bang theory? Where does structure come from? Why is the overall distribution of matter so uniform? Why is the density of the universe so close to the critical density? The Big Bang theory isn’t complete yet… Explaining the Origin of Structure:  Explaining the Origin of Structure The simple Big Bang model gives a Universe with no structure To explain why the Universe has structure, we need “inflation” What is Inflation?:  What is Inflation? A period of extremely rapid expansion when the Universe was very young. 10-38 to 10-36 seconds Regions of the Universe expanded from the size of an atomic nucleus to the size of the Solar System Slide33:  Inflation can make all the structure by stretching tiny quantum ripples to enormous size These ripples in density then become the seeds for all structures in the Universe Testing Inflation:  Testing Inflation Why is the Cosmic Microwave Background Radiation almost perfectly isotropic? The CMB is isotropic because regions now on opposite sides of the sky were close together before inflation pushed them far apart Testing Inflation:  Testing Inflation Patterns of structure observed by WMAP show the “seeds” of universe Observed patterns of structure in the Universe agree (so far) with the “seeds” that inflation would produce After Inflation:  After Inflation The rate of expansion slowed to a more stately pace Will the Universe continue to expand or will gravity eventually slow the expansion and even cause the Universe to collapse again? Will the Universe Keep Expanding Or Re-Collapse????:  it depends on the density of the Universe The critical density is 10-29 g/cm3, about one hydrogen atom per cubic meter About 25 times more than the observed mass of stars and gas But what about dark matter? there isn’t quite enough to re-collapse the Universe Will the Universe Keep Expanding Or Re-Collapse???? But the universe isn’t even slowing down…. The more we learn, the stranger it gets…:  The more we learn, the stranger it gets… The speed of a ball tossed up in the air slows down because of gravity Observations at the end of the 20th century established that the Universe is not just coasting, or slowing down because of its own gravitational pull, but actually speeding up. The speeds of very distant galaxies tell us the Universe is expanding faster today than in the past:  We observe Type Ia supernovae (exploding white dwarfs) to measure the distances of extremely distant galaxies. This tells us the Hubble Constant when the universe was younger. The speeds of very distant galaxies tell us the Universe is expanding faster today than in the past The Universe is speeding up!:  The universe is expanding faster today than it did in early times This expansion cannot be caused by ordinary matter or dark matter The acceleration suggests the possibility of a new type of repulsive force (anti-gravity) that acts on very large scales The Universe is speeding up! The New Force Is Called “Dark Energy”:  When Einstein developed the theory of general relativity, astronomers thought the Universe was “static” Einstein included a repulsive force called the cosmological constant to balance gravity (anti-gravity!) The cosmological constant was rejected when we learned the Universe was expanding The cosmological constant is now needed to explain why the Universe is speeding up The New Force Is Called “Dark Energy” WMAP’s observation of the “seeds” of structure inferred from the CMB confirm the existence of dark energy:  WMAP’s observation of the “seeds” of structure inferred from the CMB confirm the existence of dark energy Overall geometry is flat Total mass+energy has critical density Ordinary matter ~ 4.4% of total Total matter is ~ 27% of total Dark matter is ~ 23% of total Dark energy is ~ 73% of total Age of 13.7 billion years What is Dark Energy?:  A “fifth force?” …in addition to strong force (holds nuclei together) weak force (interactions of electrons) electrical/magnetic force (holds atoms together) gravity (works over large distances) Something else? We don’t know. What is Dark Energy? A brief history of the Universe:  A brief history of the Universe Courtesy of Fred Adams University of Michigan Slide45:  BIG BANG – 13.7 billion years ago, space, time, and energy burst into existence The part of the Universe that now comprises our “observable universe” was very small and very dense Why did the Universe suddenly appear???? Slide46:  INFLATION ERA – Regions of the universe rapidly expand from smaller than an atom to bigger than the Solar System. Because all of space was so compact, every part of the universe was in “contact” with every other part. Energy was uniformly distributed throughout the early universe Slide47:  PHOTON ERA - energy in the form of electromagnetic radiation dominates the Universe - visible light, X rays, radio waves and ultraviolet rays. Energy transforms into matter: quarks the first nuclei: protons, neutrons,helium The density of energy was so great that matter could not exist. As the density was gradually reduced through expansion, matter began to form. Both matter and anti-matter formed, but for some reason, there was a slight excess of matter. Slide48:  Originally, no stars Protons and electrons combined into atoms The Universe became opaque due to absorption of light by hydrogen atoms The First Dark Era Origin of the CMB – the thermal radiation of the first atoms:  Origin of the CMB – the thermal radiation of the first atoms Isotropic microwave radiation Slide50:  STELLIFEROUS ERA – the current era Atoms condensed into the first generation of stars during the first 200 million years The first stars reheated the gas (reionization) The universe remains transparent because the density is so low Galaxies formed Sun, solar system formed 4.6 billion years ago Life appeared on Earth 3.8 billion years ago Modern humans show up just 100,000 years ago The Universe in a Day:  The Universe in a Day Slide52:  DEGENERATE ERA – 10 trillion trillion trillion years after the Big Bang Planets detach from stars Stars and planets evaporate from galaxies Most ordinary matter in the universe is locked up in degenerate stellar remnants Eventually, even the protons themselves decay Slide53:  BLACK-HOLE ERA - 10,000 trillion trillion trillion trillion trillion trillion trillion trillion years after the Big Bang The only large objects remaining are black holes Eventually even the black holes evaporate into photons and other types of radiation. Slide54:  The Final DARK ERA – Only photons, neutrinos, electrons and positrons remain, wandering through a universe bigger than the mind can conceive. Occasionally, electrons and positrons meet and form "atoms" larger than the visible universe is today. From here into the infinite future, the universe remains cold, dark and empty. The History of the Universe in 200 Words or Less:  The History of the Universe in 200 Words or Less Quantum fluctuation. Inflation. Expansion. Strong nuclear interaction. Particle-antiparticle annihilation. Deuterium and helium production. Density perturbations. Recombination. Blackbody radiation. Local contraction. Cluster formation. Reionization? Violent relaxation. Virialization. Biased galaxy formation? Turbulent fragmentation. Contraction. Ionization. Compression. Opaque hydrogen. Massive star formation. Deuterium ignition. Hydrogen fusion. Hydrogen depletion. Core contraction. Envelope expansion. Helium fusion. Carbon, oxygen, and silicon fusion. Iron production. Implosion. Supernova explosion. Metals injection. Star formation. Supernova explosions. Star formation. Condensation. Planetesimal accretion. Planetary differentiation. Crust solidification. Volatile gas expulsion. Water condensation. Water dissociation. Ozone production. Ultraviolet absorption. Photosynthetic unicellular organisms. Oxidation. Mutation. Natural selection and evolution. Respiration. Cell differentiation. Sexual reproduction. Fossilization. Land exploration. Dinosaur extinction. Mammal expansion. Glaciation. Homo sapiens manifestation. Animal domestication. Food surplus production. Civilization! Innovation. Exploration. Religion. Warring nations. Empire creation and destruction. Exploration. Colonization. Taxation without representation. Revolution. Constitution. Election. Expansion. Industrialization. Rebellion. Emancipation Proclamation. Invention. Mass production. Urbanization. Immigration. World conflagration. League of Nations. Suffrage extension. Depression. World conflagration. Fission explosions. United Nations. Space exploration. Assassinations. Lunar excursions. Resignation. Computerization. World Trade Organization. Terrorism. Internet expansion. Reunification. Dissolution. World-Wide Web creation. Composition. Extrapolation? Copyright 1996-1997 by Eric Schulman . Slide56:  Last units: 81, 82, 83, 84 Complete Nov. 21 NQ by TONIGHT FINAL NQ AVAILABLE WEDS MORNING, ONLINE LAST(!) homework due Thursday Projects due THURSDAY

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