1. Announcements • No HW this week (Q4) • HW12 due on Friday, December 16 • No class on Tuesday, December 13 • Thursday schedule on Tuesday, December 13 (in lieu of Thanksgiving day): TA has office hours • Final on Thursday, December 22, 11:001:30, in Harriman 137 AST 248, Fall 2005

2. Search for Life in the Universe Chapters 12 (Part 2) & 13 Alien Civilizations AST 248, Fall 2005

3. Outline • UFOs • Crashed Aliens in Roswell, NM • Crop Circles, Abductions, etc. • Ancient Visitations • Cover-Up & Scientific Disinterest • Where Is Everybody? • Age of Civilization • Cosmic Calendar • Civilization Timescales • Youngest Civilization • Galactic Colonization • Colonization Models • Motives for/against Colonization • Possible Solutions to the Paradox AST 248, Fall 2005

4. UFOs • Appearance • Jet planes first introduced at the end of World War II  public aware of fast-moving aircrafts • First UFO claim in June 1947 • “Flew erratic, like a saucer”  flying saucer • ~50% of the public believe in the existence of UFOs • Air Force Investigation • 20-year investigation • 90% of claims discarded • Remaining 10% indeterminate • Lack of proof is no proof AST 248, Fall 2005

5. Crashed Aliens in Roswell, NM • Known facts • Rancher found crash remnants July 1947 • Military personnel picked up the debris • Remains shown next day in Fort Worth, TX • Claimed to be remains of a weather balloon • Claims by Stanton Friedman (1978) • Crash an alien spacecraft • Alien bodies also recovered • Story hushed up by military • Analysis • Project Mogul: balloon used for secret monitoring of Soviet tests • Witness accounts in seventies contradicted or discounted • Motive for secrecy not clear • Ability to keep secret highly doubtful AST 248, Fall 2005

6. Crop Circles, Abductions, etc. • Crop circles: • Claim: too accurate and too quick to be done by humans • Shown to be possible • Some admitted to be pranks • Abductions: • Sleep paralysis: common dream during rapid eye movement (REM) • Also known during day dreaming AST 248, Fall 2005

7. Ancient Visitations • Ancient drawings • Claim: pictures of aliens • Counterclaim: other possibilities abound • Nazca markings • Claim: needed unavailable knowledge • Counterclaim: did not need unavailable knowledge • Claim: could only be seen from space • Counterclaim: could be form of worship • Egyptian pyramids • Claim: Egyptians could not build the pyramids by themselves • Counterclaim: it was shown that the pyramids could be constructed with tools available then AST 248, Fall 2005

8. Cover-Up & Scientific Disinterest • Cover-up • Motive to avoid alarm: 50% already think that aliens have landed • U.S. Government notoriously unable to keep secrets known by many for a long time • All other governments need to participate in the conspiracy • Scientific disinterest • Stems from lack of evidence, not disinterest • If there was serious evidence, or the chance to obtain serious evidence, scientists would jump at it AST 248, Fall 2005

9. Where Is Everybody? • Statement of the Paradox • If our civilization is not unique, others would have formed long before us, would now be far more advanced, and would long have colonized the Galaxy • Where are they? • Von Neumann machines • Self replicating robots • Overcome distance by much longer longevity • Frank Tipler: Von Neumann machines would by now have colonized the entire Galaxy • We have seen no evidence  our civilization is unique AST 248, Fall 2005

10. Cosmic Calendar AST 248, Fall 2005

11. Civilization Timescales • Time to form a civilization :done by us in 4.6 byr • Age of Galaxy: ~10 byr • Time to form civilizations before us: 6 byr • Rate • 1011 stars x 106 probability = 105 civilizations = 1 per 6 x 104 yr • 1011 stars x 106 probability / 20 (heavy element abundance) = 5,000 civilizations = 1 per 105 yr • 1011 stars x 109 probability = 100 civilizations = 1 per 6 x 107 yr AST 248, Fall 2005

12. Youngest Civilization • Assume youngest civilization 105 years older than us • At a distance of 8 x 104 ly, we would still see it at an age of 2 x 104 yr AST 248, Fall 2005

13. Colonization Models • Light travel time through the Galaxy • 105 yr • Nuclear-powered travel at 0.1c • 106 yr • Coral Model (0.1c) • Colonize a star and then move on • Add ~ 150 yr per step of 50 yr • Multiplies expansion time by 4 AST 248, Fall 2005

14. Motives for/against Colonization • For: • “Human” nature • Humankind spread quickly • And then spread more by displacing other people • Against: • Population growth: too expensive • Conquering a backward civilization: not worth defeating “cavemen”, although natural resources may be valuable • Conquering a more advanced civilization: “cavemen” unlikely to defeat us AST 248, Fall 2005

15. AST 248, Fall 2005

16. Possible Solutions to the Paradox • We are alone • The numbers in the Drake equation are poorly known, so we are possibly alone • Civilizations but no colonization • Technical difficulties: our estimates may be too optimistic • Sociological reasons: population and energy problems solved another way • Self destruction: we have already come close to nuclear confrontation • There is a Galactic civilization • They are keeping us in a “nature reserve” • We are not interesting • We may be interesting sometime in the future, when our action manifests our cosmic “maturity” AST 248, Fall 2005

17. Thank you for your attention Good luck on the final: Thursday, December 22, 11:001:30 in Harriman 137 (here) AST 248, Fall 2005