Observational !

Lecture I! C. Porciani! AIfA Bonn! Summer Semester 2010! Lecturers!

Cristiano Porciani Kaustuv Moni Basu! [email protected] [email protected]! AIfA office 1.30 AIfA office 1.24 ! 0228 - 733664 0228 - 736786!

Lectures: Wednesday 11:15-12:45 !

Office Hours: by appointment!

Course website: http://www.astro.uni-bonn.de/~kbasu/astro845.html!

C. Porciani! Observational Cosmology! I-2! Exercise classes!

Who wants credits for this course should attend the exercise classes and do homework (not much). ! Also little projects are available. ! Hands up who is interested!

We need to decide when the classes will be held! First class will review FRW metric and basic cosmology!

TA: Anna Elia! [email protected] !

C. Porciani! Observational Cosmology! I-3! Textbooks!

• There will be no official textbook for the course!

• The class will focus on the most recent advancements in cosmology which are often not yet textbook material!

• Some lecture notes and the slides will be made available in pdf format !

• Recommended readings will be suggested from time to time!

C. Porciani! Observational Cosmology! I-4! Feedback!

• Feedback and interaction is greatly appreciated!

• This is your class! Feel free to stop me any time if you are not understanding something!

• There are no stupid questions, please, do not be scared to ask!

• We will always start a class with questions regarding the previous one!

C. Porciani! Observational Cosmology! I-5! Assessing the right level of the class!

• Please write down your name, e-mail address, and semester (or Master, PhD, etc.) !

• Hands up who took a basic cosmology class!

• Hands up who is confident knowing the FRW metric!

• Hands up who knows and what is the critical density of the !

• Hands up who knows what is!

C. Porciani! Observational Cosmology! I-6! WHAT IS THIS COURSE ABOUT?!

C. Porciani! Observational Cosmology! I-7! Cosmology + ET = Cosmetology Cosmology!

• Etymology: Κοσμοσ “the physical world” + λογια “discourse”!

• The science of the origin, the structure, and the development of the universe as a whole! All science learning begins with questions!

• What does the Universe look like?! • What is it made of?! • Is it finite or infinite?! • How old is it?! • How will it end?! • What does physics say about the Universe?! • What does the Universe say about physics?! • How did the structures we see form?! • When did they form?! • Where do we fit into this picture?!

C. Porciani! Cosmology and LSS! I-10! The atypical lecture of today!

• What is this course about? ! It is mainly about the future of cosmology!

“There is no future without tradition” (O. Marquard)!

• The birth of modern cosmology ! The human mind and the Universe ! (historical - epistemological approach)!

• Observational facts and definitions!

C. Porciani! Observational Cosmology! I-11! The ancient universe!

Laconian amphora,! 6th century BC, ! Vatican Museums, Rome!

C. Porciani! Observational Cosmology! I-12! The only instrument available!

C. Porciani! Observational Cosmology! I-13! Xinhua/ Xu Suhui Photo!

C. Porciani! Observational Cosmology! I-14! C. Porciani! Observational Cosmology! I-15! The Nebra sky disk, Bronze Age, 1600 B.C. (??), Nebra, Germany !

C. Porciani! Observational Cosmology! I-16! The birth of astronomy!

• Early astronomy was about repeating phenomena and the measure of time (calendar, seasons)!

• As far as we know, there was no explanatory attempt, the idea was to describe regularities. The study of sky phenomena was useful to sailors and for agriculture. !

• Astronomy was always linked to astrology, myth and religion!

• The first scientific revolution happened in the 8th century B.C. when Babylonians started developing logically consistent, predictive models of the solar system based on some assumptions!

C. Porciani! Observational Cosmology! I-17! The Aristotelic universe!

• Aristotle (384-322 BC), building upon the work of Eudoxus (409-356 BC), developed the classic model of antiquity!

• The Universe is composed of 55 concentric spheres (grouped in 8 ``heavens’’) made of aether (quintessence) with the Earth at the center !

• The ``Primum Mobile’’ imparts motion to the spheres!

• Distinction between the supra- lunar and sub-lunar worlds! C. Porciani! Cosmology and LSS! I-18! The first heliocentric system!

• Aristarchus of Samos (310-230 BC) proposed the first heliocentric system for the Universe!

• If the Earth was changing position with respect to the , should have been observed!

First measured ! by Bessel in 1838! • No parallax was detected (0.3 arcsec for 61 Cygni)! and the heliocentric model was quickly forgotten (importance of )!

C. Porciani! Cosmology and LSS! I-19! The Ptolemaic Universe!

• The troubling observations of varying planetary brightness and retrograde motion could not be explained by Aristotle’s model! • Hipparchus (190-120 BC) and Ptolemy (85-165 AD) “improved” it to accommodate them! • Ptolemy’s conception of a geocentric, finite and ethernal Universe lasted for almost 2000 years!!

C. Porciani! Cosmology and LSS! I-20! The classic universe!

Johannes Vermeer, 1668 (Musée du Louvre, Paris)! Sandro Botticelli, 1483-1485 (Galleria degli Uffizi, Firenze)!

C. Porciani! Observational Cosmology! I-22! Copernicus, Tycho Brahe & Kepler! (1470-1543) (1546-1601) (1571-1630)!

C. Porciani! Cosmology and LSS! I-23! The celestial realm is mutable!

Amazed, and as if astonished and stupefied, I stood still, gazing for a certain length of time with my eyes fixed intently upon it and noticing that same placed close to the which antiquity attributed to Cassiopeia. When I had satisfied myself that no star of that kind had ever shone forth before, I was led into such perplexity by the unbelievability of the thing that I began to doubt the faith of my own eyes.

Tycho Brahe

C. Porciani! Observational Cosmology! I-24!

Galileo Galilei (1564-1642)! a troublemaker! Galileo made a splash!

Hans Lippershey (1570-1619) Thomas Harriot (1560-1621) Sidereus Nuncius! !

The Ptolemaic model is definitively disproved:!

• The Moon is as rocky as the Earth !

• The Sun has spots and rotates!

• Jupiter has moons!

• Venus has phases!

• There are stars which are not visible without a !

C. Porciani! Cosmology and LSS! I-29! (1642-1727)!

Authentic revolution:! New Mechanics + Law of Universal Gravitation ! Perfect agreement with observational data! Celestial mechanics is a solved problem! !

C. Porciani! Cosmology and LSS! I-30! The clockwork Universe!

• Newton’s Cosmology admits the existence of absolute time and absolute space (they exist also where there is no matter and they will always do)!

• The Universe of Newtonian physics is perfectly deterministic!

• In principle, we can predict the entire future of the Universe from a knowledge of the initial positions and velocities!

C. Porciani! Cosmology and LSS! I-31! Beyond clockwork: the 20th century!

• Gravitating systems of more than 2 bodies are chaotic (small differences in the initial conditions lead to divergence of the solutions)!

• Quantum Mechanics has a probabilistic which stems from the act of measurement!

C. Porciani! Cosmology and LSS! I-32! The modern universe!

Vincent Van Gogh, 1889 (The Museum of Modern Art, New York)! The universe with naked eyes!

Photo: Kerry-Ann Lecky Hepburn Tintoretto, 1575-1580 (The National Gallery, London)! Measuring the size and the ingredients of the universe!

C. Porciani! Observational Cosmology! I-36! The “Realm of the Nebulae”!

Galileo resolved the (MW) into faint stars!

Kant (1724-1804) proposed that the MW was a disk of stars and that there could be similar “island ” distributed throughout space!

Messier (1730-1817) and Herschel (1738-1822) found many “nebulae” (fuzzy, diffuse looking objects which appeared at fixed positions on the sky)!

Parsons (1800-1867) observed that some nebulae had a spiral structure !

C. Porciani! Cosmology and LSS! I-37! The “Realm of the Nebulae”!

Helium was identified by emission lines in the Sun spectrum in 1868 (by Janssen & Lockyer) and later found on Earth 1895. !

In 1864 the English astronomer Williams Huggins postulated the existence of a new element (dubbed “nebulium”) to explain the strong green emission lines found in what is nowadays known as Cat’s Eye nebula.!

In 1927 Ira Sprague Bowen showed that these emission lines were due to (electric-dipole) forbidden transitions of doubly ionized oxygen.!

C. Porciani! Cosmology and LSS! I-38! The Milky Way!

• Based on stellar counts, Kapteyn (1851-1922) developed a lens-shaped model of the MW ! The realm of the nebulae!

• Charles Messier (1730-1817) !

• Wilhelm Herschel (1738-1822) !

• In 1845 William Parsons (Earl of Rosse) discovered the “spiral nebulae” using its “Leviathan of Parsonstown” (1.83 m)! The origin of the nebulae!

Island universe hypothesis! Nebular hypothesis! • The spiral nebulae are • The spiral nebulae are other Milky Ways made swirling gas clouds! of stars! • Nearby and internal to • Very distant and our Milky Way! external to our ! • Might be forming solar • Kant (1775), Alexander systems! von Humboldt (1845)! • Laplace (1796)!

Heber D. Curtis (but Sun in the centre) Harlow Shapley (but Sun off centre) Harvard Observatory Director Pickering:

“A great observatory should be carefully organized and administered as a railroad… A great savings may be effectuated by employing unskilled and therefore inexpensive labor, of course under careful supervision.” Henrietta Swann Leavitt (1868-1921)!

• “It is worthy of notice that brighter variables have longer periods” !

In 1924 the Universe grows bigger!

• In 1924, (1889-1953) detected some stars in the M31 nebula!

• Using the period-luminosity relation determined by H. Leavitt (1868-1921) he found a distance to M31 of nearly a million light-years, a factor of 10 larger than the size of the Milky Way!

• This clearly made M31 a “galaxy” on its own right!

C. Porciani! Cosmology and LSS! I-45! Our home!

Our galaxy itself contains a hundred billion stars; ! it's a hundred thousand light years side to side. ! It bulges in the middle - sixteen thousand light years thick -, ! but out by us it's just three thousand light years wide. ! With thirty thousand light years from galactic centrepoint ! we go round every two hundred million years - ! and our galaxy is only one of millions, of billions, ! in this amazing and expanding universe! !

Eric Idle, The Galaxy Song ("The Meaning of Life") ! Our neighbours

M31 The Andromeda Galaxy 2.56 million light years away

M33 The Triangulum Galaxy 3 million light yearsaway C. Porciani! Cosmology and LSS! I-47! What about progress in the theoretical description of the universe?!

C. Porciani! Observational Cosmology! I-48! The birth of space-time!

In 1905, Einstein (1879-1955) publishes his theory of special relativity (building upon the work of Lorentz). This is based on two postulates:! • The laws of physics take the same form in all inertial frames (regardless of their velocity) ! • The speed of light c is a universal constant, the same in any inertial frame! • The theory leads to the relativity of simultaneity and then to the concept of space-time (introduced by Minkowski)! • A metric tensor tells how to compute the distance between any two points (events)!

C. Porciani! Observational Cosmology! I-49! are time machines!

• Looking out in space is looking back in time due to the finite speed of light!

• Imagine you get a postcard from some friends. You know how they were then not how they are now!! The Relativistic Universe!

• In 1916 Einstein publishes the General Theory of Relativity and in 1917, (1872-1934) uses it to describe an expanding Universe!

• explains gravity as the curvature of space-time!

• Energy tells space-time how to curve, space-time tells matter how to move!

• No action at a distance, just GEOMETRY!

C. Porciani! Cosmology and LSS! I-51! An observational surprise: ! cosmic expansion!

C. Porciani! Observational Cosmology! III-52! Most have redshifted spectra!

Vesto Slipher! 1912! The quest for the expansion!

• 1912: discovers that most spiral nebulae have a redshifted spectrum!

• From 1917, people starts using GR to describe the Universe. Einstein favours a static (but unstable) model!

• 1917: Willem de Sitter finds that GR admits a cosmological metrical in an empty universe!

• 1922: Alex Friedmann finds that an expanding universe is a solution to GR field equations!

• 1927: Georges Lemaitre independently derives the expanding solution and is told by Einstein "Vos calculs sont corrects, mais votre physique est abominable”!

C. Porciani! Observational Cosmology! I-54! The quest for the expansion!

• 1929: Edwin Hubble (with Milton Humason) finds that there is a linear correlation between redshift and distance suggesting the reality of cosmic expansion!

• This is one of the pillars of modern cosmology!!

• 1935: Robertson & Walker show that the FLRW solution is the only one that can describe a homogenous and isotropic universe !

Hubble 1929, Hubble & Humason 1931! C. Porciani! Observational Cosmology! I-55! Cosmological redshift!

Lab. Frame

Cosmic frame

λ • Cosmological redshift: the wavelength of EM signals is stretched by the cosmic expansion. !

• Spectra are shifted in frequency towards the red by a factor

1+z = (present-day size of the universe)/(size at photon emission)=a(t0)/a(tem)!

1+ z = λobs /λem

C. Porciani! Observational Cosmology! III-56!

€

A galaxy at redshift 6!

C. Porciani! Observational Cosmology! I-58! C. Porciani! Observational Cosmology! I-59! Redshift vs time!

C. Porciani! Observational Cosmology! I-60! The universe is a huge, old and nearly empty place!!

It is covenient to use specially suited units to describe its properties

Local universe! 30 • Mass: solar mass, 1 M= 1.989 × 10 kg! • Length: , 1 pc = 3.0856 × 1016 m! 26 • Luminosity (work): solar luminosity, 1 L= 3.90 × 10 W !

Distant universe!

• Expansion rate: Hubble parameter, Ho = 100 h km/s/Mpc! 9 -1 • Time: Hubble time, 1/Ho = 9.778 × 10 h yr! -1 • Length: Hubble radius, c/Ho = 2997.9 h Mpc! 11 2 -3 • Density: ρ = 2.7755 × 10 Ωh M Mpc = = 1.8791 × 10-26 Ωh2 kg m-3 ≈ 11 Ωh2 protons m-3 !

C. Porciani! Observational Cosmology! I-61! or steady state?!

C. Porciani! Observational Cosmology! I-62! C. Porciani! Observational Cosmology! I-63! Cosmic abundances! 1925 Cecilia Payne: The abundances of chemical elements in stars are remarkably uniform. The Sun and other stars are composed almost entirely of hydrogen and . ! “almost certainly not real” (Henry Norris Russell)!

Solar system abundances!

C. Porciani! Observational Cosmology! I-64! The controversy!

• 1930s: Lemaitre proposes the idea of the primeval “cosmic egg” from which the whole universe derives!

• 1948: the “alphabetical paper” Alpher, Bethe & Gamow (Herman later refused to become Delter) proposes that the universe started in a very hot and dense phase. ALL chemical elements are built via neutron capture and beta decay at very early times. Problems: no stable isotopes exist with 5 and 8 nucleons, decay happens within 10-18-10-20 sec. Iron (26) is very common, gold (79) is rare, the model cannot explain why.!

• 1948: Hoyle, Gold & Bondi propose the steady-state model where the universe looks always the same under the combined action of cosmic expansion and matter creation through the C-field. The chemical elements are “cooked” by nuclear reactions in stars. Problem: difficult to produce the required amount of helium !

C. Porciani! Observational Cosmology! I-65! C. Porciani! Observational Cosmology! I-66! The new Genesis!

In the beginning God created radiation and ylem. And ylem was without shape or number, and the nucleons were rushing madly over the face of the deep.

And God said: "Let there be mass two." And there was mass two. And God saw deuterium, and it was good.

And God said: "Let there be mass three." And there was mass three. And God saw tritium and tralphium [Gamow's nickname for He-3], and they were good. And God continued to call number after number until He came to transuranium elements. But when He looked back on his work He found that it was not good. In the excitement of counting, He missed calling for mass five and so, naturally, no heavier elements could have been formed.

God was very much disappointed, and wanted first to contract the universe again, and to start all over from the beginning. But it would be much too simple. Thus, being almighty, God decided to correct His mistake in a most impossible way.

And God said: "Let there be Hoyle." And there was Hoyle. And God looked at Hoyle… and told him to make heavy elements in any way he pleased.

And Hoyle decided to make heavy elements in stars, and to spread them around by supernovae explosions. But in doing so he had to obtain the same abundance curve which would have resulted from nucleosynthesis in ylem, if God would not have forgotten to call for mass five.

And so, with the help of God, Hoyle made heavy elements in this way, but it was so complicated that nowadays neither Hoyle, nor God, nor anybody else can figure out exactly how it was done. Amen. C. Porciani! Observational Cosmology! I-67! C. Porciani! Observational Cosmology! I-68! C. Porciani! Observational Cosmology! I-69! Cosmic backgrounds!

• The cosmic microwave background (CMB) dominates the radiation content of the Universe! • It has been serendipitously discovered by Penzias & Wilson in 1965! • It contains nearly 98% of the radiant energy and 99.9% of the photons!!

C. Porciani! Observational Cosmology! I-70! COBE-DMR RESULTS (1992)!

The CMB temperature is highly isotropic with intrinsic fluctuations of the order of 1 part every 105!

The CMB has a blackbody spectrum with T≈2.73 K!

C. Porciani! Observational Cosmology! I-71! The rest of the story!

• 1949: Alpher & Herman predict the existence of the CMB as a relic of the hot early phases of the universe! • 1950s: Gamow, Alpher, Herman refine their predictions for the CMB temperature! • 1950: Hoyle invents the term “Big bang”! • 1954: Hoyle discovers the triple alpha resonance! • 1957: B2FH show how heavy elements are produced in stars! • 1964: Penzias and Wilson serendipitously detect the CMB! • 1964: Hoyle & Tayler show that about 23-25% of helium by mass is created by primordial nucleosynthesis in the hot universe independently from the detailed initial conditions! • 1967: Wagoner, Fowler & Hoyle show that also helium 3 deuterium and lithium 7 are produced in the big bang while all the heavier elements must be synthesized into stars!

C. Porciani! Observational Cosmology! I-72! C. Porciani! Observational Cosmology! I-73! !

• The synthesis of light elements takes place at a cosmic age between 1 and 1000 s and depends on the baryon density Ωb!

• A detailed comparison of the predicted element relative abundances with the observational data allows to test our cosmological model!

• One single value for Ωb can explain all the abundances at once (this is a one of the “pillars” supporting the big bang model)!

• The best current estimate is 2 Ωb h = 0.0214 ± 0.002 from the D/H ratio measured in absorption line systems!

C. Porciani! Observational Cosmology! I-74! Weighing galaxies with gravity! !

Evidence: ! (only gravitational)!

• Galaxy dynamics in galaxy clusters!

• Rotation curves of spiral galaxies!

• Cosmic microwave background anisotropies!

• Gravitational lensing!

The Large Hadron Collider! The contemporary universe!

Roman Ondak, 2007 (The Museum of Modern Art, New York)! Atmospheric transmission!

C. Porciani! Observational Cosmology! I-80!

Courtesy of Stefan Seip Courtesy of the HUDF team The deepest image of the universe in the optical waveband

It contains 104 galaxies in a solid angle corresponding to 1/50 of the Moon’s cross section

The whole sky corresponds to 12.7 million times more solid angle

Galaxies are the fundamental building blocks of the distribution of luminous matter How are galaxies distributed on the sky?! The large-scale structure!

Colless et al. 2003

Each tiny little dot marks the position of a galaxy like our own Milky Way The (SDSS, York et al. 2000, Zehavi et al. 2005)

How did the LSS form?! A path from simplicity to complexity! Temperature anisotropies!

Resolution ≈ 7 °

ΔT −5 Resolution ≈ 0.2 - 0.9° T ≈10

€ Gravitational instability! density

mean density position

• Cosmic capitalism: the rich gains more, the poor looses more!

• Gravity makes matter flow from underdense to overdense regions! The cosmic expansion history: ! another observational surprise!

The accelerating universe! Cosmic concordance!

Reid et al. 2009 • Statistics of temperature anisotropies in the microwave background! Mantz et al. 2009 • Statistics of the galaxy distribution!

• Abundance of galaxy clusters!

• Hubble diagram of supernovae Ia! What counteracts gravity?!

Michael Turner 1998 What counteracts gravity?! The cosmic budget! • The elegant universe (Brian Greene)!

• The extravagant universe (Robert Kirshner)!

• The preposterous universe (Sean Carroll)!

• Maybe the most fundamentally mysterious thing in basic science (Frank Wilczek)!

• Not only queerer than we suppose but queerer than we can suppose! (J.B.S. Haldane)! Why no one noticed it before?!

• The measured value corresponds to a matter density of 0.000000000000000000000000006 kg per cubic meter (less than the mass of 4 protons)!

• The best vacuum made in a physics laboratory has a density which is higher by a factor of a billion!

• A cube stretching from Bonn to the Moon only contains 340 g of dark energy!

• A cube stretching from Bonn to the Sun only contains 20 million Kg of dark energy, a fraction 0.00000000000000000000001 of the solar mass!

• A cube enclosing the whole Galaxy contains nearly 1 trillion solar masses of dark matter but only 3 million solar masses of dark energy!

• A cube as large as the visible universe contains 73% of the mass in dark energy! What do we know of dark energy?!

• Smoothly distributed through space, doesn’t fall into galaxies or clusters!

• Constant density (or nearly constant) through time, not diluted by cosmic expansion!

• Invisible to ordinary matter, only detected by gravity! Vacuum energy!

• In quantum field theory the vacuum has a non vanishing energy!

• This is observable: Lamb shift, Casimir effect!

• Does vacuum gravitate?!

Quantum theory overpredicts the observed value by a factor between 1,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000! and ! 1,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000, 000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000, 000,000!