Chapter 18Distribution of GalaxiesMotion of GalaxiesAge of the UniverseThe “Center” of the UniverseLooking Back: Olbers’ ParadoxLooking Back: Cosmic HorizonCosmic Microwave BackgroundCosmic Microwave BackgroundFormation of GalaxiesWhere is the “center of the universe”?How old is the universe?What is the “cosmic horizon”?The “echoes” of the big bang are known as the…Origin of the UniverseOrigin of the ElementsRadiation, Matter, AntimatterCurvature of the UniverseThe Inflationary UniverseThe “Flatness Problem”The “Horizon Problem”Slide 22What caused antimatter to stop being produced?Slide 24Which of the following does inflation NOT directly explain?Future Expansion of the UniverseDensity of the UniverseAcceleration of the UniverseDark EnergyThe Future of the UniverseSlide 31What is dark energy?What is the ultimate fate of the universe?Slide 34Chapter 18CosmologyDistribution of GalaxiesMotion of Galaxies•Basically all galaxies receding from us.•Space itself is expanding.•There is no “center” to the expansion.Age of the Universe•If everything’s expanding, then long ago everything must have been closer together.•Implies such a high density that protons and neutrons touch (“Primeval Atom”).•Calculate the age based on these inferences —> 14 Billion years.The “Center” of the Universe•Looks the same wherever you stand.•“Cosmological principle” = Everyone thinks they’re at the center.•The concept of a “center” is meaningless.Looking Back: Olbers’ Paradox•If the universe is infinitely old and infinitely large, the whole sky should be bright even at night.•Three solutions: Universe has finite size Universe has finite age Wavelengths redshifted too much to seeLooking Back: Cosmic Horizon•Light from more than 14 billion light years away hasn’t had time to reach us.•We can only see 14 billion light years in any direction.•“Light year” odd to define in an expanding universe.•“Light travel time distance”Cosmic Microwave Background•The Early universe was very hot and opaque.•“Recombination era:” Universe becomes transparent.•About 3,000 K when this happened.•Based on Wein’s Law: (1,000 nm at the time, 1 mm now)Cosmic Microwave Background•Eventually the signal was found by Bell Telephone Laboratories in 1965.•Comes from the entire sky.•Only the Big Bang Theory can explain CMB.Formation of Galaxies•Small irregularities in CMB became galaxies.•Computer simulations: small differences in CMB can’t do it alone.•Dark matter clumped together before normal matter.Where is the “center of the universe”?A. We are at the center of the universeB. The center of the universe is located in another galaxyC. There is no such thing as the center of the universeHow old is the universe?A. 6,000 yearsB. 14 million yearsC. 14 billion yearsD. 14 trillion yearsWhat is the “cosmic horizon”?A. The edge of the universeB. The edge of the observable universeC. The edge of our superclusterD. Black holesThe “echoes” of the big bang are known as the…A. Cosmic horizonB. Cosmic microwave backgroundC. Cosmic microwave ovenD. Cosmic redshifOrigin of the UniverseOrigin of the Elements•Just before the CMB, the universe was as hot and dense as a star.•Amount of Helium (and friends) depends on the density and temperature at this time, and how long those conditions lasted.•Oldest stars are 24% Helium.•Current composition of universe consistent with predictions of Big Bang Theory.Radiation, Matter, Antimatter•E = mc2•High energy photons —> particle + antiparticle•Particle + antiparticle —> high energy photons•Requires really high temperatures•Once universe cooled sufficiently, no more pars of particles were produces, and annihilation was left to run its course.•1 part in a billion “asymmetry” between matter and antimatter.Curvature of the Universe•Mass and energy cause space to be “curved”•Curvature can be positive, flat, or negative.•Can determine flatness of our universe based on fluctuations in the CMB.The Inflationary Universe•Simulate high temperatures of early universe in labs.•Can simulate back to 1 µs after the big bang.•Physics (as we know it) works back until 10-43 sec.•Strong and electroweak split at 10-35 sec, causing inflation.•Einstein’s “cosmological constant”•Inflation helps explain two major features of our universe.The “Flatness Problem”•Why is the universe so “flat”?•Flat universes are highly unstable. Must have been “fine tuned”?•Inflation explains this problem.The “Horizon Problem”•Opposite points on CMB are outside each other’s cosmic horizon, but are still basically the same temperature.•Things must have gotten “smoothed” when everything was smaller.•The (small) fluctuations must have existed before inflation started.In which curvature of universe would you eventually return to your starting point if you traveled in a straight line?A. NegativeB. Zero (flat)C. PositiveWhat caused antimatter to stop being produced?A. Cosmic microwave backgroundB. The universe cooled below the necessary temperatureC. It annihilated with regular matterD. Massive catastrophic impactThe temporary increase in the rate of expansion of the early universe is known as…A. Cosmic microwave backgroundB. Planck timeC. InflationD. Theory of EverythingWhich of the following does inflation NOT directly explain?A. Why the CMB is so uniformB. The relative concentrations of different elementsC. Why the universe is so “flat”Future Expansion of the Universe•“Big freeze” vs “big crunch”•Which one? Depends on balance between gravity and the “force” of the expansion.•Need to know the mass (or density) of the universe to know answer.Density of the Universe•Calculated in a simple way, comes out to 3*10-30 g/cc•“Critical density” = border between collapse and expansion forever (formula depends on Hubble’s constant)•ΩM = ρactual / ρcritical (Should be = 1 based on inflation, measured to be ⅓)Acceleration of the Universe•Look at rate of expansion in past by “standard candle” of Type Ia supernova.•Can predict brightness of these events based on redshift.•Universe was expanding slower in the past, so expansion must be speeding up (shouldn’t happen because gravity)•Cosmological constant = repulsive force of space on itself = “dark energy”Dark Energy•Repulsive force