The History and Philosophyof Astronomy (Lecture 23: Steady State vs Big Bang)Instructor: Volker BrommTA: Jarrett JohnsonThe University of Texas at AustinAstronomy 350L (Fall 2006)Steady State vs Big Bang Universe Permanence vs change!ParmenidesHeraclitus• change is illusion!• time has no beginning• “What is, cannot not be!”• everything is in perpetual flux!• basic element: fire• “Panta Rhei!”Origin of the Big Bang Theory• 1922: an expanding universe (solving Einstein’sequations of General Relativity without cosmological constant)Alexander Friedmann(1888-1925)Origin of the Big Bang Model• 1927: Lemaitre independently (re-) discovers theexpanding-universe solutions of GRAbbe Georges Lemaitre(1894-1966)Lemaitre meets Einstein(Pasadena, 1933)Origin of the Big Bang Model• Lemaitre: Imagine that you run expansion of universe backwards in time!Cosmic timeobserver• in distant past: universe was much denser and hotter!Origin of the Big Bang Model• 1931: Lemaitre’s “Primeval Atom”:• Primeval atom: super-heavy, radioactive!• Radioactive decay somehow triggers expansion! Lemaitre: “Father of the Big Bang”Origin of the Big Bang Model• George Gamow1904 (Odessa) – 1968 (Boulder)•distinguished career in nuclear physics(“tunnel effect”)•1948: theory of Big Bangnucleosynthesis(with R. Alpher)• famous popularizer of science(“Mr. Tompkins in Wonderland”)The Riddle of the Chemical ElementsAbundance vs atomic number• Hydrogen and helium by far the most abundant cosmic elements• Why: 1 He atom per 10 H atoms?• Why are all the other elements so very rare?Big Bang Nucleosynthesisylem• Big idea (Alpher and Gamow 1948): Synthesizeall elements during earliest, hot and dense, phase• Raw material = “Ylem”: primordial soup of protons,neutrons, electrons, and photons“Hot Big Bang”Big Bang Nucleosynthesis• Great success: Big Bang nucleosynyhesis cansuccessfully explain Helium abundance (1 He atomper 10 H atoms)• published (April 1, 1948) as Alpher, Bethe, & Gamow(the “alphabetical paper”: alpha, beta, gamma…)Big Bang NucleosynthesisRalph AlpherRobert HermanBig Bang Nucleosynthesis• Big problem: theory doesn’t work for heavier elements:- He+neutron, He+proton unstable!- He + He ( Be) unstable!Modern View of Nucleosynthesis1. Hydrogen, helium: Big Bang2. All other elements: Interior of stars• Bridging the “Helium-carbon gap”: Triple-alpha process (Edwin Salpeter, 1952)Modern View of Nucleosynthesis• Successful theory of creating the elements in stars:- Burbidge, Burbidge, Fowler, & Hoyle (B2FH 1957)Predicting Cosmic Background Radiation• Big idea (Alpher and Herman 1948): Out ofprimordial fireball in early universe  an intense seaof photons that is still around us todayphotonsPredicting Cosmic Background Radiation• Expansion of Universe stretches light towardslonger wavelength (i.e., redder and less energetic)• Cosmic background today: redshifted intomicrowave region of electromagnetic spectrum!Predicting Cosmic Background Radiation• Prediction (1948): Cosmic microwave background (CMB)at a (radiation) temperature of ~ 5 Kelvin• Why was CMB not discovered then???( CMB was eventually discovered in 1965 by serendipity)- failure to explain creation of elements beyond Helium!- breakdown of communication between theorists and experimentalists (radio astronomers)- general disregard for anything related to “Early Universe”Vatican endorses the Big Bang• Pope Pius XII (1939 – 58)- Eugenio Pacelli•1951: official endorsement- speech `The Proofs forthe Existence of God in theLight of Modern NaturalScience’• Big Bang = moment of CreationSoviet Union bans the Big Bang• Marxism-Leninism• philosophy: dialectical materialism• materialism  nocreation of matter outof nothing (matter, andtherefore the universe,must have existed forever!)•Soviet scientists endorsing Big Bang were sent to `Gulag’!Cosmic Age Problem• Age of the universe (in Big Bang model) shorterthan estimated age of the Earth (~ 4 billion years)!!!• recession speed = (Hubble) constant x distance• v = H0x d• (H0=500 km s-1Mpc-1)- Hubble’s originalvalue5002History of H00200400600800100012001920 1930 1940 1950 1960 1970 1980 1990 2000DateH0 (km/s/Mpc)Compilation by John HuchraBaade identifies Pop. I and II Cepheids“Brightest stars” identified as H II regionsJan OortThe Steady State Alternative (1948) • worked out at Cambridge University, EnglandHermann Bondi(1919-2005)Thomas Gold(1920-2004)Fred Hoyle (1915-2001)Hoyle coins the term “Big Bang”• Both Hoyle and Gamow fought a PR battle!Fred Hoyle • 1950: BBC radio interview• derogative term for rivaltheory to his own steady-state• before that, “Big Bang” wascalled “dynamic evolving model”Steady State AlternativeSteady state universeEvolving universe (“Big Bang”)• density changes with time• past different from present• beginning of time (“Big Bang”)• density constant over time• universe never changes• no beginning of timeSteady State AlternativeSteady state universeEvolving universe (“Big Bang”)• How does density change over time?Steady State Alternative• How can density be constant despite cosmic expansion?• continuous creation of matter (“C-field”)• Need: 1 atom per liter per billion yearsSteady State AlternativeSteady state universeEvolving universe (“Big Bang”)• How and when is matter created?timetime• all of matter at beginning of time• small amounts of matterall the time• For both models: matter is created out of nothing!Steady State Alternative• steady-state equilibrium: Patterns remain, but matter flows constantly `through’ them • A: steady state: pattern (here: volume) doesn’t change• B: static case: nothing changes (e.g., Einstein’s Universe)Einstein’s Eternal (and static) Universe• 1917: Einstein constructs model of the universethat is eternal and static • finite but without boundary (spatially closed)• balance betweenattractive gravityand repulsive cosmological constant(“anti-gravity”)Steady State Alternative• steady-state theory obeys perfect cosmological principle • cosmological principle : universe looks everywherethe same (on average)  isotropy and homogeneity• perfect cosmological principle (PCP): universe lookseverywhere and everywhen the same(homogeneity in space and time)• aesthetic appeal of PCP because of higher