INTRODUCTION TO COSMOLOGY ALEXEY GLADYSHEV (Joint Institute for Nuclear Research & Moscow Institute of Physics and Technology) RUSSIAN LANGUAGE TEACHER PROGRAMME CERN, November 2, 2016 Introduction to cosmology History of cosmology. Units and scales in cosmology. Basic observational facts. Expansion of the Universe. Cosmic microwave background radiation. Homogeneity and isotropy of the Universe. The Big Bang Model. Cosmological Principle. Friedmann-Robertson- Walker metric. The Hubble law. Einstein equations. Equations of state. Friedmann Equations. Basic cosmological parameters. The history of the Universe from Particle physics point of view. The idea of inflation. Problems and puzzles of the Big Bang Model. The Dark Matter. Cosmology after 1998. The accelerating Universe. The Dark Energy and cosmological constant. November 2, 2016 A Gladyshev “Introduction to Cosmology” 2 What is Cosmology ? COSMOLOGY – from the Greek κοσμος – the World, the Universe λογος – a word, a theory studies the Universe as a whole, its history, and evolution November 2, 2016 A Gladyshev “Introduction to Cosmology” 3 Cosmology before XX century ~ 2000 BC Babylonians were skilled astronomers who were able to predict the apparent motions of the Moon, planets and the Sun upon the sky, and could even predict eclipses ~ IV century BC The Ancient Greeks were the first to build a “cosmological model” within which to interpret these motions. They developed the idea that the stars were fixed on a celestial sphere which rotated about the spherical Earth every 24 hours, and the planets, the Sun and the Moon, moved between the Earth and the stars. November 2, 2016 A Gladyshev “Introduction to Cosmology” 4 Cosmology before XX century II century BC Ptolemy suggested the Earth-centred system. Stars and planets rotate around the Earth. The model was very successful at reproducing the apparent motion of the planets. November 2, 2016 A Gladyshev “Introduction to Cosmology” 5 Cosmology before XX century XVI century Copernicus proposed a heliocentric system. The Earth rotated and, together with the other planets, moved in a circular orbit about the Sun. But the observational evidence of the time favoured the Ptolemaic system! November 2, 2016 A Gladyshev “Introduction to Cosmology” 6 Cosmology before XX century Tycho Brahe realised that if the Earth was moving about the Sun, then the relative positions of the stars should change as viewed from different parts of the Earth's orbit. But there was no evidence of this shift, called parallax. Either the Earth was fixed, or else the stars would have to be fantastically far away. Beginning of the XVII century Galileo discovered Jupiter’s moons. And if moons could orbit another planet, why could not the planets orbit the Sun? November 2, 2016 A Gladyshev “Introduction to Cosmology” 7 Cosmology before XX century Kepler discovered the key to building a heliocentric model. The planets moved in ellipses, not circles, about the Sun. Newton later showed that elliptical motion could be explained by his inverse-square law for the gravity. 1750 Thomas Wright noticed that the luminous stripe observed in the night sky and called the Milky Way could be a consequence of spatial distribution of stars: they could form a thin plate, what we call now a galaxy. November 2, 2016 A Gladyshev “Introduction to Cosmology” 8 Cosmology before XX century At that time many faint and diffuse objects were known and listed. The generic name was nebulae. Soon after the proposal of Wright Emmanuel Kant suggested that some of these nebulae could be some other clusters of stars far outside the Milky Way. XIX century Bessel finally measured the distance to the stars by parallax. The nearest star turned out to be about 15 million, million km away from the Earth! (The Sun is 150 million km away.) November 2, 2016 A Gladyshev “Introduction to Cosmology” 9 Cosmology before XX century At the beginning of the century some physicist observed the first spectral lines. 1842 Johann Christian Doppler argued that if an observer receives a wave emitted by a moving body, the wavelength that he will measure will be shifted proportionally to the speed of the emitting body with respect to the observer 1868 Sir William Huggings found experimentally that the spectral lines of some neighboring stars were shifted towards the red or blue end of the spectrum November 2, 2016 A Gladyshev “Introduction to Cosmology” 10 Cosmology in the XX century 1910-1922 Vesto Melvin Slipher discovered the red shift in galactic spectra. 1916 Albert Einstein discovered the General Theory of Relativity 1922-1924 Alexander Friedmann found solutions of Einstein equations which could describe the expanding Universe. November 2, 2016 A Gladyshev “Introduction to Cosmology” 11 Cosmology in the XX century 1929 Edwin Powell Hubble established that some of the nebulae in the sky were indeed distant galaxies comparable in size to our own Milky Way. He also made the remarkable discovery that these galaxies seemed to be moving away from us, with a speed proportional to their distance from us. 1933 Fritz Zwicky discovered the hidden mass in galactic clusters, later called “the Dark Matter” November 2, 2016 A Gladyshev “Introduction to Cosmology” 12 Cosmology in the XX century 40’s of the XX century Ralph Alpher, Hans Bethe, George Gamow and others developed a hypothesis of the Hot Big Bang and predicted a cosmic microwave background radiation and calculated the relative abundances of the elements hydrogen and helium that might be produced in a Hot Big Bang November 2, 2016 A Gladyshev “Introduction to Cosmology” 13 Cosmology in the XX century 1965 Arno Penzias, Robert Wilson discovered the pridicted cosmic microwave background radiation with a temperature around 3 К 1979-1980 Alan Guth, Alexei Starobinsky, Andrei Linde, David Kirzhnitz suggested a hypothesis of inflating Universe November 2, 2016 A Gladyshev “Introduction to Cosmology” 14 Cosmology in the XX century 1986 Margaret Geller and John Huchra discovered the large-scale structure of the Universe at distances 25-100 Mpc 1992-1993 COBE (COsmic Background Explorer) satellite detected the first anisotropies in the CMBR: slight fluctuations in the temperature of the radiation, about 10-5 at scales 10° November 2, 2016 A Gladyshev “Introduction to Cosmology” 15 Cosmology in the XXl century 1998 Collaborations “Supernova Cosmology Project” and “The High-Z Supernova Search” discovered that at large scales the Universe expands with acceleration 1998-2003 Missions BOOMERANG (Balloon Observations Of Millimetric Extragalactic Radiation ANd Geophysics) and MAXIMA (Millimeter Anisotropy eXperiment IMaging Array) confirmed that the geometry of the Universe is very close to the flat one November 2, 2016 A Gladyshev “Introduction to Cosmology” 16 Cosmology in the XXl century 2001-2010 A NASA Explorer mission WMAP (Wilkinson Microwave Anisotropy Probe) made fundamental measurements of cosmology. WMAP has been extremely successful, producing our new Standard Model of Cosmology. Full analysis of the data is now completed. 2009-2015 Plank – a European Space Agency observatory – mapped the anisotropy of CMB at microwave and infra-red frequencies, with high sensitivity and small angular resolution. November 2, 2016 A Gladyshev “Introduction to Cosmology” 17 System of units in Cosmology The system of units one selects for a problem often reveals much about physics of the problem. In cosmology one uses the “natural” system ck B 1 Plank Speed Boltzman constant of light constant -1 -1 In this system [ ENERGY ] = [ MASS ] = [ TEMPERATURE ] = [ LENGTH] = [ TIME ] 1 GeV = 1.16 1013 К 1 К = 0.8 10–13 GeV 1 GeV = 1.8 10–24 g 1 GeV–1 = 2 10–14 cm 1 cm = 5 1013 GeV–1 1 GeV–1 = 6.6 10–25 s 1 s = 1.5 1024 GeV–1 November 2, 2016 A Gladyshev “Introduction to Cosmology” 18 Measuring distances / Parallax Units of length in cosmology: A parsec is defined as the distance from the Sun which would result in a parallax of 1 second of arc as seen from Earth. The word "parsec" is an abbreviation and contraction of the phrase "parallax per second." 1 pc = 3.262 light years = 3.086 1018 cm 1 Mpc = 106 pc November 2, 2016 A Gladyshev “Introduction to Cosmology” 19 Scales in the Universe Stars – surrounding astronomical objects 30 Typical masses M ~ 1 – 10 M M= 2 10 kg Galaxies – the basic building blocks in the Universe 6 12 Typical masses M ~ 10 – 10 M Typical size L ~ 0.1 Mpc Typical distance D ~ 1 Mpc November 2, 2016 A Gladyshev “Introduction to Cosmology” 20 Scales in the Universe Many galaxies are gravitationally bound to groups or clusters with 2 – 1000 galaxies. Big clusters are the biggest objects in the Universe bound by gravitation. Typical size L ~ 10 Mpc Conglomerations of galaxies – regions of space with higher than average density On scales bigger than 100 Mpc the matter distribution is known to be homogenious The observable universe – the distant the light has travelled since the Big Bang, L ~ 104 Mpc – the biggest distance we can observe November 2, 2016 A Gladyshev “Introduction to Cosmology” 21 Basic observational facts The most important cosmological observations are: Expansion of the Universe Cosmic microwave background radiation Large scale isotropy and homogeneity Light element abundances in the Universe November 2, 2016 A Gladyshev “Introduction to Cosmology” 22 Measuring velocities / The red shift Galaxies have a set of absorption and emission lines identifiable in their spectra, whose characteristic frequencies