* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Before people could understand the history of the universe, they had
History of supernova observation wikipedia , lookup
Outer space wikipedia , lookup
International Year of Astronomy wikipedia , lookup
Wilkinson Microwave Anisotropy Probe wikipedia , lookup
Anthropic principle wikipedia , lookup
Astrobiology wikipedia , lookup
History of astronomy wikipedia , lookup
International Ultraviolet Explorer wikipedia , lookup
Observational astronomy wikipedia , lookup
Dark energy wikipedia , lookup
Extraterrestrial life wikipedia , lookup
Big Bang nucleosynthesis wikipedia , lookup
Shape of the universe wikipedia , lookup
Dialogue Concerning the Two Chief World Systems wikipedia , lookup
Hubble's law wikipedia , lookup
Cosmic microwave background wikipedia , lookup
Geocentric model wikipedia , lookup
Hubble Deep Field wikipedia , lookup
Copernican heliocentrism wikipedia , lookup
Expansion of the universe wikipedia , lookup
Observable universe wikipedia , lookup
Fine-tuned Universe wikipedia , lookup
Ultimate fate of the universe wikipedia , lookup
Structure formation wikipedia , lookup
Timeline of astronomy wikipedia , lookup
4,000 Years of Cosmology (The Abbreviated Version) What is Cosmology? The study of the Universe as a whole From the start of time until now... And until the end of time. Before people could understand the history of the Universe, they had to know its geography... Thales • 6th century BC, philosopher and traveler • brought back to Greece knowledge and records of the Babylonians and Egyptians • first ideas that lay between the mythologies and true science • Note: he believed the Earth was flat and floated on water like a log Aristotle lived from 384 to 322 BC 3 experimental proofs that the Earth was round Believed the Earth was the center of the Universe and the Sun, Moon, planets, and a sphere containing all the "fixed" stars revolved around it What’s Popular is Not Always Right, and What’s Right is Not Always Popular Most Greeks believed Aristotle and his ideas The exception (a century later) ... Aristarchus, who thought the Earth moved around the Sun - he found very few supporters for his ideas - often overlooked in the history of heliocentric ideas What’s Popular is Not Always Right, and What’s Right is Not Always Popular Hipparchus 100s BC, compiled a star catalog giving a magnitude or comparative brightness scale calculated the Moon's distance from the Earth Claudius Ptolemaeus (better known as Ptolemy of Alexandria) came along 300 years later first astronomer to make truly scientific maps of the heavens The Ideas of Ptolemy • Believed that the Sun, Moon, and planets circled the Earth • Planets sometimes appear to travel backward? -each moved in a small circle (epicycle) that was orbiting Earth • Summarized the theory in the Almagest -written in the 140 AD -theory was believed for about 1500 years Copernican Theory Polish monk Nicolaus Copernicus says “Sun is the center.” The Church, however, says Earth was central – Copernicus' theory was heresy! – He did not publish it until the day he died (On the Revolution of the Celestial Spheres) Two events made the "Copernican revolution" inevitable: • Brahe's precise observations of the sky • Galileo's use of the telescope. Tycho Brahe • Danish astronomer • In 1572, saw brilliant “new star” in the sky in the constellation Cassiopeia; supernova! • In 1604, a second supernova was observed • These discoveries undermined the cornerstone of the Ptolemaic system, i.e., outermost sphere contained all the stars and it was unchanging New “Eyes” on the Skies • In 1609, Italian scientist Galileo Galilei heard about the spyglass, made one for himself, and turned it on the heavens • One of the first discoveries was four moons circling Jupiter • He revealed a miniature version of Copernicus' solar system, with the moons moving around the planet in simple, circular orbits • The Catholic Church later forced Galileo to recant his ideas and live out his life under house arrest, but his discoveries had already changed the face of astronomy Saving Face • British genius Isaac Newton unwittingly gave the Church a "way out” • Newton put mathematics to observations - the equations to describe the relationships observed for motion, and by gravity - applied his equations to Kepler's observations (it fit almost perfectly) • The conclusions were indisputable: Copernicus had been right all along (actually Aristarchus had been!) Saving Face • It is the force of gravity which keeps all the planets in their elliptical orbits around the Sun • Newton's Laws say that nothing is naturally at rest; all heavenly bodies should be constantly moving, with no limits on space and time • Newton believed that the Universe was eternal and infinite; this made the Church happy • It was an uneasy reconciliation, but one that allowed science to move forward unimpeded Big Bang • In 1917, Albert Einstein proposed a description of the Universe based on his Theory of General Relativity • In Belgium, Georges Lemaitre came up with his own model when he heard that the Universe was expanding • Universe began as a “primeval atom” • Hot and dense • Explosion caused expansion to start • Lemaitre can be called the “father of the big bang” Note: He was an ordained priest before turning to cosmology. Big Bang; As We Now Know It • George Gamow, a Russian-American physicist (late 1940s), conceived of Big Bang we know today • He and his colleagues proposed - elements created in very brief period early in expansion of Universe - predicted an afterglow, still should be present arising from hot, early phase - largely forgotten until afterglow was discovered in the 1960s Note: Gamow was also a popularizer of science, wrote poetry, and did research in genetics George Gamow 1904 - 1968 Hey Look at Me… I’m Expanding! • Edwin Hubble in 1920’s; major breakthrough in understanding of Universe • For centuries, astronomers believed Milky Way entire Universe • In 1923, Hubble was among the first to show that the fuzzy patches they saw in the sky through their telescopes were whole other galaxies, not parts of the Milky Way What Hubble Saw In 1929, by looking at the spectra of these galaxies, he concluded that they were speeding away from us - the Universe was expanding! QuickTime™ and a GIF dec ompres sor are needed to s ee this pic ture. Edwin Hubble 1889 - 1953 Note: Before turning to astronomy, Hubble was a lawyer. Why Do We Believe the Big Bang Theory? Observations, Observations, Observations! • Expansion of the Universe • Origin of the cosmic background radiation • Nucleosynthesis of the light elements • Formation of galaxies and large-scale structure Other Theories • Steady State Theory • Chronometric Theory incompatible with CMB observations, incorrect source counts, predicts redshift is quadratic function of distance • Tired Light Theory no known mechanism to degrade photon energy, contradicts high redshift supernova observations Steady State Theory • Universe had a beginning? Not appealing to all scientists • In 1948, Fred Hoyle, Hermann Bondi, and Tommy Gold, came up with Steady State Theory - Universe has no beginning and no end -Although expanding, it stays in perfect balance like a pool kept full to overflowing by a trickle from a faucet -The "faucet" is the continuous creation of matter from energy Steady State Theory (cont) • They showed that only one atom per cubic mile of space per hour was needed • Even this amount proved to be the theory's undoing - It defied the laws of physics; It did not match observations Evidence Against the Steady State Theory • Background cosmic heat radiation discovered • Amount of helium observed in the Universe exactly fit what was predicted by the big bang • Radio astronomers found that galaxies were more crowded together in the past - meaning the idea of an unchanging universe was incorrect Basking in The Afterglow • In 1963/1965, physicists Arno Penzias and Robert Wilson started to search for faint radio signals (actually microwaves) from the outskirts of the Milky Way Galaxy - famous antenna located in Holmdel, New Jersey Penzias and Wilson •Bedeviled by a persistent interference (a constant signal from all over the sky) equivalent to temperature of - 454 °F (-270 °C or 3 Kelvin) • They thought the signal was from pigeon droppings in the telescope, but colleagues soon realized that they had found the afterglow predicted by Gamow Inflation Solves Some Big Bang Problems • In 1979, particle physicist Alan Guth - Stanford Linear Accelerator Center - interested in the Grand Unification Theory of Forces - calculations led to the idea of "cosmic inflation” (brief period of rapid expansion in the early Universe) • It explains why the Universe is so big and so smooth, why (at least) four different forces act in it today, and where the vast amounts of matter came from. Accelerating Expansion? • In 1998, Science magazine says "breakthrough of year" Universe is expanding at an accelerating rate! • For over ten years astronomers studying expansion of Universe by measuring: - Redshifts - Brightness of Type Ia supernovae Accelerating Expansion • Note: Type Ia supernovae are stars that explode in thermonuclear cataclysms brighter than entire galaxies • Ideal "standard candles" to survey the Universe - Their light curves and spectra are all nearly alike and they are bright enough to be seen across billions of light-years • By 1998, many of these supernovae analyzed in detail, leading scientists to conclude that the expansion of the Universe is not slowing, but accelerating! HST Observations of Distant Supernova What Drives the Acceleration? • The supernova data strongly suggest that Universe is filled with an unidentified form of energy which is the cause of the accelerating expansion • This is called "Dark Energy"