The History and Philosophyof Astronomy (Lecture 25: Modern Developments II:Inflation)Instructor: Volker BrommTA: Jarrett JohnsonThe University of Texas at AustinAstronomy 350L (Fall 2006)Big Bang Theory: Successes and Problems• Successes: - Hubble expansion of galaxies- Helium and hydrogen abundance- cosmic microwave background• Problems: - requires fine-tuning in initial conditionsRobert Dicke: Princeton’s Titan• 1916 - 97• important contributionsboth in theory and observation• cosmic microwave background- renewed prediction- detection strategy(`Dicke radiometer’)- beaten by Penzias and Wilsonwho detected CMB by serendipity• pointed out fundamental riddlewith standard Big Bang model(“flatness problem”)The Flatness ProblemSize of Universe vs. Age• TINY difference in density in early universe translateinto HUGE difference in long-term fate!The Flatness Problem• In Einstein’s General Relativity, the universe’s densityis reflected in its overall geometry (`curvature’)• Omega=actual density/critical densityflatopenclosedcriticaldensitylowdensityhighdensityThe Flatness ProblemOmega vs. Age• Tiny deviations from Omega=1 briefly after Big Bangvery rapidly develop into huge ones!• Flatness Problem: Why is the universe, after billions of years,observed to be still so close to critical (Omega=1)???The Horizon ProblemAll-sky projection of cosmic microwave radiation• Big Q: Why is the universe so similar in alldirections? (`isotropy’)usThe Horizon Problem• A=B  requires: (1) causal contact (but there was no time!)(2) fine tuning (to extreme degree)• Big Q: Why is the universe so similar in alldirections? (`isotropy’)Standard Big Bang: Fine-Tuning Problem• Within standard Big Bang model, need to postulatefine-tuning of conditions briefly after the Big Bang???• Our Universe appears highly improbable• Was the universe created with fine-tuned initialconditions so as to allow our existence?(so-called `anthropic principle’)The Particle Physics Revolution (1970s)Electromagnetic forceGUT• GUT= GrandUnified Theory- 1974: Sheldon Glashowand Howard Georgi• Early in the universe, all 4 forces of nature wereunified into one `superforce’• With time, the forces attain separate identityThe GUT Phase Transition• 10-34seconds after Big Bang: Universe has cooledbelow critical temperature for Grand Unification(i.e., EM = weak force = strong force)• Symmetry between strong and electroweak forcewill be `broken’• Analogy for `spontaneoussymmetry breaking’ (SSB):- glasses in dinner tablesetting- initially, they are all of equalstatus- after SSB: symmetry is broken (one glass is special)The GUT Phase Transition• Before symmetry breaking (during Grand Unified Era):- 3 forces are unified- `Identity fields’ (technically `Higgs fields’) whicheventually are responsible for making forces different, allhave zero valuesPotential energyHiggs fieldsymmetric statebroken-symmetry state• After symmetry breaking: Higgs fields have non-zerovalue  strong force is different from electroweak forceDelayed Phase Transition: `False Vacuum’• Higgs field does not immediately `roll away’ fromzero point• Universe remains for a while in high-energy state- so-called `false vacuum’Potential energyHiggs fieldsymmetric statebroken-symmetry state`false vacuum’`true vacuum’Weird Properties of the False Vacuum• `False vacuum’ has never been observed inlaboratory, but we can speculate about its behavior!• False vacuum has negative pressure (=tension) Normal gasFalse Vacuum• positive pressure• expanding bubbleloses energy• negative pressure• expanding bubblegains energyAlan Guth: Inventing Inflation• Born 1947 (New Brunswick, NJ)• 1980: Professor at MIT • 1981: Inflationary Universe- “Spectacular Realization:Universe did go through an episode of tremendousexpansion briefly afterthe Big Bang”• natural solution for Big Bangfine-tuning mysteryWeird Properties of the False Vacuum• `False vacuum’ has negative pressure (=tension)• According to Einstein, negative pressure hasrepulsive gravity (`anti-gravity’)timeFalsevacuum• expanding universe, containing false vacuum,creates more and more false vacuum  runawayexpansion  inflationGuth’s Inflationary Universe• Universe expands by tremendous factor (~1050)between 10-34and 10-32secondsRadius of Universe vs AgeThe End of Inflation• Inflation ends when Higgs field finally `rolls down’into `true vacuum’ (minimum energy) state• strong force is now distinguished from electroweak one• universe now contains only positive pressure materialPotential energyHiggs fieldsymmetric statebroken-symmetry state`false vacuum’`true vacuum’Inflation solves the Flatness Problem• Even if universe started out with curvature, inflationwill smooth this out, and drive universe to flatness!Exponential Expansion of space• Important prediction: Omega = 1 (“Space is flat”)• Spectacularly confirmed in 2003 by WMAP satelliteInflation solves the Horizon Problem• Inflation has blown up microscopic region inearly universe (small enough for causal interactions)to size way beyond our current observable universeThe Multiverse• maybe there are (infinitely?) many distinct universes,each one triggered by a phase transition, leadingto inflation?!time• eternal inflation (A. Linde)- eternal (no beginning intime)- self-reproducingThe Dark Side of the Universe• Big Q: What is the universe made of?• consensus view ofearly 21stcentury (WMAP):- 4% normal matter (`baryons’) (stars, gas, people…)- 23% dark matter- 73% dark energy• Dark Energy has negative pressure, and thusblows apart universe (2ndinflation-like episode?)• Is Dark Energy connected to inflaton field?The Inflationary Universe• 1970s: Realization that Big Bang has problems- flatness problem- horizon problem- magnetic monopole problem • Present-day cosmic accelaration- Dark Energy has negative pressure  anti-gravity- we ve just entered 2ndinflation-like phase of runaway expansion• 1980s: Inflationary Universe Theories developed- Alan Guth first proposes inflation (1981)- inflation is triggered during GUT symmetry breaking- universe spends some time in `false vacuum’ state- false vacuum drives space apart at accelerating