Philosophy

1. One purpose of a liberal arts education is to make your head a more interesting place to live inside of for the rest of your life. President McPherson, Bryn Mawr College

2. Philosophy Knowledge, and understanding, are wild things, to be hunted down and subdued. Ignorance, stupidity and superstition are infectious, treatable conditions; but their successful treatment requires the cooperation of the patient.

3. Introduction • Books • Syllabus • Other stuff you’ll need

4. What is Astronomy? • Oldest “science” dating back to ~4000 B.C. • First of sciences to be quantitative • Unusually appealing since it’s often observational and outside • Modern astronomy is primarily astrophysics • Study of laws guiding celestial phenomena • Study of theories which explain celestial phenomena

5. What Astronomy Isn’t • Astronomy is not, repeat… not ASTROLOGY • Astrology is an ancient religion • Results of many studies: • No evidence exists that astrology has any predictive power at any statistical level of confidence. Period. • But… the records of ancient astrologers have been useful for studying paleoastronomy

6. Some Basic Observations from a Geocentric (Homocentric) P.O.V. • Every day • Sun moves from east to west • Every night • Stars move from east to west • When it can be seen, • Moon moves east to west… • Slightly slower than the stars

7. Some Basic Observations from a Geocentric (Homocentric) P.O.V. • About every month (~28 days) • Moon cycles from new to full to new • Moon moves ~1 h (15°) east every 24 h • Which means it rises ~1 h earlier every day • Every night • A constellation sets ~4 min earlier • Therefore the sun appears to move from one zodiacal constellation to another • Every 12 months • The same constellation will be in the south

8. Some Basic Observations from a Geocentric (Homocentric) P.O.V. • The Zodiac • Sun moves along a path through a specific group of constellations • Path = ecliptic • Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpius, Sagittarius, Capricornus, Aquarius, Pisces • Every now and then a bright “star” wanders along the ecliptic, gradually moving east, but generally following the stars’ nightly motion.

9. The Ecliptic Constellations

10. As we proceed through the course, we will jump back and forth through time. We will start with modern thought then take a historical view and work our way back to the 20th century (and beyond). But first…. The Persistence of Memory, S. Dali

11. Some Important Definitions • Astronomical Unit, AU • Distance of   • 1.5 x 108 km (93 million miles) • c = s.o.l. • Cosmic speed limit: • 3.00 x 108 m/s, 186,000 mi/s • Distance can be measured by the amount of time the light traveled from an object. • Recall d = r x t

12. Some More Important Definitions • Light year, ly • Distance light travels in 1 yr • 9.461 x 1012 km (that’s 9.5 trillion km to you and me) • That’s… 9,461,000,000,000 km • 5.879 x 1012 mi (5.9 trillion miles!) • Parsec, pc • Parallax-second (but that’s not important now) • 3.26 ly

13. A Short History of the Universe

15. Galaxies: Hubble Space telescope image

16. Edwin Hubble, who started out as a lazy, rich kid, became one of the most important of all astronomers.

17. Hubble (1921) Galaxies move away from us at a speed proportional to their distance

18. Hubble’s Discovery of Expansion

25. Gravitational Collapse • Regions with more particles (higher density) become gas clouds • Gas clouds become stars and galaxies • Galaxies congregate together in filaments, groups and clusters

26. But we are inside one of these galaxies, so all we see are the nearby stars. We can see other galaxies if we use a telescope

27. The Cosmic Microwave Background Still, limited evidence for a Big Bang. Gamow and Peebles predicted that there should be a “glow” left over from this huge, hot expansion in the microwave region of EM radiation. Objects and even “empty” space give off a characteristic spectrum of electromagnetic radiation depending on their temperature: called “blackbody” radiation. You glow in the infrared. Gamow calculated that if the temperature then was 20,000 degrees; today it would be about 6 degrees.

28. antenna Penzias Wilson In 1964, the radiation predicted by Gamow wasfinallydetected, withthisantenna … … by Penzias and Wilson, twophysicistsfrom the Bell labs, whogot the Nobel prize in 1978

29. In fact, the snowthat one cansee on an untuned TV isalso due in part to that radiation emitted by the Universe as itwasjust 380,000 yearsold !

30. COBE Fluctuations Wilson MicrowaveAnisotropy Probe Gamow waswrong. It’s not 6 K, but ~2.7 K. This means the universeisolderthanhepredicted.

31. In 1992, the COBE satelite (Cosmic Background explorer) gave the first image of the radiation  Before correction of the Earthmovementaround the Sun  Before correction of the microwaveradiation emitted by our own galaxy  The final image of the microwaveRadiation

32. The CMBR and the Copernican Principle The Copernican Principle: The universe should appear the same regardless of the location of the observer Just how homogeneous and isotropic is the universe? Reasonably so for galaxies on scales of 100’s of millions of light years. What about the CMBR? -- the temperature is the same to a part in 10,000 in every direction in the sky! Small variations only observed in 1993. Now studied with great precision.

33. More support for BB Cosmology Results of detailed nucleosynthesis calculations: • The fraction of the universe made of • Baryons = protons + neutrons

34. More support for BB Cosmology: Helium Abundance in the Universe • At the late time (as we shall see) of 3 minutes in the history of the universe, atomic nuclei were created. • Big Bang theory predicts that the relative abundances of hydrogen and helium were: • Hydrogen 76% • Helium 24% • Lithium 1 part per 1010 • Due to nuclear fusion in stars since the Big Bang, current abundances: • Hydrogen 73% • Helium 26% • Everything else 1%

35. COMPOSITION OF THE UNIVERSE If 5% of the universe is baryons, what is the rest? From studies of CMBR, of distant supernova explosions, and from Hubble and ground-based observations we know: • 5% baryons (protons, neutrons) • 35% dark matter (zero pressure) • 65% dark energy (negative pressure)

36. A Confusing Picture: Where Do We Stand? We have a good understanding of the history of the universe, both from observations and well understood theory, from t = 180 seconds. BUT: • We don’t know why there are baryons at all! • We don’t know what constitutes 95% of the energy/matter of the universe. • We know that the universe underwent a period of inflation. But we have little idea what inflation is.

37. A Confusing Picture: Where Do We Stand? To answer these questions, we need to know how the universe behaved when the temperature was extremely high. Temperature equates to energy. So we need to know about high energies. Experiments at higher energy accelerators at CERN (Geneva) and Fermilab (Chicago) are testing our understanding at extremely high energy.

38. What do we know? • Particle physicists know the laws of nature on scales down to one-thousandth the size of an atomic nucleus. The ``Standard Model”. This corresponds to temperatures about 1,000,000 times those of nucleosynthesis. BUT THIS IS NOT ENOUGH TO ANSWER OUR QUESTIONS • Experiments at higher energy accelerators at CERN (Geneva) and Fermilab (Chicago) are testing our understanding at even shorter distances. Expect to discover new phenomena.

40. PDG Wall Chart

41. Summary of Cosmologic Measurements • The Big Bang theory is consistent with observations. Specifically • Hubble Telescope can view the universe ~1,000,000,000 years after the Big Bang • The COBE satellite can view the universe ~300,000 years after the Big Bang • The Hydrogen/Helium ratio can view the universe ~3 minutes after the Big Bang