Through a Glass Darkly: Dark Energy and The Fate of the Universe

1. Through a Glass Darkly: Dark Energyand The Fate of the Universe CLAS Saturday Scholar Lecture

2. A Scientific History of the Creation of the Universe • What was the Universe like during its earliest moments? • Brief description of the key eras since the Big Bang • Note: Cosmology doesn’t address WHY creation occurs CLAS Saturday Scholar Lecture

3. Earliest ideas about cosmology: A story of three (very clever) ancient Greek Astronomers : Aristarchus, Eratosthenes, Ptolemy CLAS Saturday Scholar Lecture

4. Aristarchus of Samos (c. 250 BCE) Determined relative size of moon (w.r.t Earth), distance to Sun CLAS Saturday Scholar Lecture

5. Lunar Eclipse Movie (Notice radius of Earth in Shadow) CLAS Saturday Scholar Lecture

6. Moon’s diameter observed to be ~ 1/3 Earth’s shadow size CLAS Saturday Scholar Lecture

7. Eratosthenes (276 - 195 BC) • Measured Circumference of the Earth (within 10% of modern value! ) • Sun is at the zenith in the city of Syene at noon on the summer solstice. • But at the same time in Alexandria, it is 7 from the zenith. CLAS Saturday Scholar Lecture

8. Eratosthenes’s Method for Finding the Circumference of the Earth CLAS Saturday Scholar Lecture

9. Claudius Ptolemy (AD 100-170) Almagest • star catalogue • instruments • motions & model of planets, Sun, Moon His model fit the data, made accurate predictions, but was horribly contrived! CLAS Saturday Scholar Lecture

10. Age-old problem: How does one explain retrograde motion of the ‘wandering stars’? Movie. Click to play. Images of Saturn and Jupiter every 2 weeks for 6 months CLAS Saturday Scholar Lecture

11. Ptolemy’s Geocentric Model • Earth is at center • Sun orbits Earth • Planets orbit on small circles whose centers orbit the Earth on larger circles CLAS Saturday Scholar Lecture

12. “Standard Model” of the Universe c.100AD-1600AD CLAS Saturday Scholar Lecture

13. Nicholaus Copernicus (1473-1543) • Polish canon (religious leader) • Suggested sun-centered (heliocentric) solar system • He thought Ptolemy’s model was contrived • Yet he believed in circular motion! • His model doesn’t fit observations any better than Ptolemy’s geocentric model! CLAS Saturday Scholar Lecture

14. Copernicus’ (heliocentric) explanation of retrograde motion CLAS Saturday Scholar Lecture

15. Horoscope written by Kepler found last year at UCSC library Kepler’s Boss: Tycho Brahe Johannes Kepler (1571- 1630) Finds elliptical orbit for Mars CLAS Saturday Scholar Lecture

16. Kepler’s model for the Solar System: A Concentric Series of Crystalline Spheres CLAS Saturday Scholar Lecture

17. Galileo’s discovery (1610) of Jupiter’s moons with his telescope showed that Earth was not the center of all orbits strongly supported a heliocentric model CLAS Saturday Scholar Lecture

18. Galileo’s discoveries of Venus’ phases with his telescope showed that Venus must orbit the Sun strongly supported a heliocentric model . Venus is clearly smallest when it is at superior conjunction and largest when it is close to inferior conjunction. CLAS Saturday Scholar Lecture

19. Galileo’s observation of the phases of Venus was the final evidence which buried the geocentric model. Geocentric Heliocentric No gibbous or full phases! All phases are seen! Galileo observed all phases! CLAS Saturday Scholar Lecture

20. Sir* Isaac Newton (1642 – 1727) “the greatest physicist who ever lived…” As a young faculty member at Cambridge University (c.1665) As Warden of the Royal Mint (1705) * Newton was knighted by Queen Anne. However, the act was "an honor bestowed not for his contributions to science, nor for his service at the Mint, but for the greater glory of party politics in the election of 1705" CLAS Saturday Scholar Lecture

21. “Standard Model” of the Universe c. 1650 AD CLAS Saturday Scholar Lecture

22. 18th - 19th Century:Astronomers Study of Properties of Stars (and lots of Comets) CLAS Saturday Scholar Lecture

23. Some stars occur in vast groups: Globular Clusters and Nebulae CLAS Saturday Scholar Lecture

24. Importance of stellar spectra 1: : Lines determine what are stars made of (like fingerprints) CLAS Saturday Scholar Lecture

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26. Importance of stellar spectra 2: Determine speed of stars (and galaxies) CLAS Saturday Scholar Lecture

27. I’m the boss The Harvard College Observatory Women Astronomers c.1910(they systematically classified stars based on their spectra) CLAS Saturday Scholar Lecture

28. Home Cosmology c.1900:Only one galaxy (ours!) CLAS Saturday Scholar Lecture

29. Curtis: Nebulae are entire ‘Island Universes (other galaxies) Is the Milky Way Galaxy the Entire Universe? The Curtis –Shapley DebateSaimthsonian Institure, Washington, DC 1920 Shapley: Nebulae are nearby stars, gas,dust CLAS Saturday Scholar Lecture

30. 1925: Hubble [former Rhodes scholar and lawyer] determines distance to Andromeda ‘Nebula’ : it’s another Galaxy 2 Million light-years away – Curtis wins debate! CLAS Saturday Scholar Lecture

31. Hubble expansion is measured using Doppler shift of spectra of galaxies CLAS Saturday Scholar Lecture

32. 1929: Hubble makes the most important cosmological observation of the century: Universe is expanding! CLAS Saturday Scholar Lecture

33. At t=0 The Universe has radius = 0 (Big Bang!) Age of Universe derived from the Hubble expansion Ho=72 ± 8 km/s Age = 1/Ho = 13.6 · 109 yrs CLAS Saturday Scholar Lecture

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35. Historical origins of the Big Bang model • Georges LeMaitre, a Belgian priest and mathematician, proposed (1920’s) that the expansion of the universe can be traced to an exceedingly dense ‘primeval atom’ • … when the whole universe exploded in “fireworks of unimaginable beauty” and with a “big noise” • Einstein, after listening to a lecture by LeMaitre said‘This is the most beautiful and satisfactory explanation of creation to which I have ever listened.”  • LeMaitre used the term ‘Cosmic Egg’. Now known as the Big Bang theory CLAS Saturday Scholar Lecture

36. The Hubble expansion implies that the Universe emerged single highly dense state: The Big Bang. • LeMaitre (1902’s) first proposed a ‘Cosmic Egg’ cosmology • In the 1940s, based on Hubble’s Law, George Gamow proposed the universe began in a colossal explosion. • In the 1950s, the term BIG BANG was coined by an [unconvinced] Sir Fred Hoyle. • Sci Fi fans: Sir Fred Hoyle (Astronomer Royal of England) wrote an excellent science fiction novel ‘The Black Cloud’ • In the 1990s, there was an international competition to rename the BIG BANG with a more appropriate name, but no new name was selected. CLAS Saturday Scholar Lecture

37. The farther we look into space, the farther back in time we are seeing Note that there is a farthest distance (‘particle horizon’) corresponding to VHubble = c. Regions farther away cannot be seen! CLAS Saturday Scholar Lecture

38. Most distant object [a galaxy] ever seen (formed ~500 Million yr after big bang – 13.4 Billion yr ago! CLAS Saturday Scholar Lecture

39. Galaxies first formed about 500-1000 million yrs after Big Bang brown color represents neutral Hydrogen Movie. Click to play. CLAS Saturday Scholar Lecture

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41. 1965: Second most astonishing cosmological in history: Discovery of Cosmic Background Radiation (CBR) • In 1965 radio astronomers Penzias and Wilson accidentally discovered The microwave radiation that fills all space is evidence of a hot Big Bang. • They were trying to measure the radio ‘noise’ of the galactic halo, but found (an annoying) weak excess isotropic noise • The signal was consistent with a radiation from a thermal source at 3° K. • A paper had just been written (but not yet published) predicting exactly this radio noise from the big bang. • Penzias & Wilson won the Nobel Prize for this discovery in 1978 CLAS Saturday Scholar Lecture

42. The CBR Spectrum and Maps • Since 1965 many observations have confirmed the CBR and measured its spectrum • The satellites COBE (1990) and WMAP (2003) have made detailed maps of the CBR. • These observation show: • The spectrum is exactly thermal with T= 2.73°K • It is isotropic • There are [very small] irregularities in the brightness across the sky CLAS Saturday Scholar Lecture

43. Decoupling Era Matter and radiation no longer interact if temperature is cooler than ~3,000 K Hot (T>> 3,000 K) Cool (T < 3,000 K) At an age ~300,000 years, the universe was finally cool enough from its initial primordial fireball that electrons and protons could combine to form atoms (era of recombination). CLAS Saturday Scholar Lecture

44. The microwave sky map shows large-scale Doppler shifts . You are looking at the remnant radiation of the ‘ashes’ of the Big Bang glowing 300,00 years after creation CLAS Saturday Scholar Lecture

45. 1980’s: Discovery of Dark Matter CLAS Saturday Scholar Lecture

46. Dark Matter in Galaxy Clusters causes Gravitational Lensing (requires 5x- 10x more mass than all known matter) CLAS Saturday Scholar Lecture

47. Curvature of Space-time (Universe) • General Relativity: local space-time is curved (positively) by presence of masses • What about OVERALL curvature of Universe (not near any masses)? • The geometry of the universe depends on the combined average mass density of all forms of matter and energy. The three possibilities are: • ZERO CURVATURE: Two parallel beams of light never intersect – the universe is flat. • POSITIVE CURVATURE: Two initially parallel beams of light gradually converge – the universe is spherical and is closed. • NEGATIVE CURVATURE: Two initially parallel beams of light gradually diverge – the universe is hyperbolic and is open. • In principle, we can measure (e.g. using long laser beams in a triangle, but not practical) CLAS Saturday Scholar Lecture

48. Curvature of space-time CLAS Saturday Scholar Lecture

49. 1998: The universe appears to be filled with dark energy. • Our observations suggest that the universe is flat. • This conflicts somewhat with our observation that all known radiation, matter, and dark matter only account for ~ 30% of the total density of the universe. • There must be an additional source somewhere – dark energy. CLAS Saturday Scholar Lecture

50. Supernovae of type Ia all have (nearly) the same peak luminosity: can be used to measure distance! CLAS Saturday Scholar Lecture