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Final Exam

Final Exam. Comprehensive Most questions from Ch. 15-18, some from Ch. 4-14, few from Ch. E-3 Multiple choice plus few short answer questions Please study: Midterm exams (available on homepage) Homework Activities Textbook Powerpoint slides. Green Bank (or Drake) Equation.

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Final Exam

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  1. Final Exam • Comprehensive • Most questions from Ch. 15-18, some from Ch. 4-14, few from Ch. E-3 • Multiple choice plus few short answer questions • Please study: • Midterm exams (available on homepage) • Homework • Activities • Textbook • Powerpoint slides

  2. Green Bank (or Drake) Equation • Estimated number of technological civilizations present in the Milky Way galaxy is given by the average rate of star formation (R*)  fraction of stars having planetary systems (fP)  average number of planets within the habitable zone for various types of star and star system (NP)  fraction of habitable planets that develop life (fL)  fr. of life-bearing planets on which intelligence appears (fI)  fraction of intelligent life forms that develop technology (fT)  average lifetime of a technological civilization (T) • Could be 100 to 1 billion (?)

  3. Pessimistic Example • Estimated number of technological civilizations present in the Milky Way galaxy: N = (R*=10/year) (fP=10%) (NP=1) (fL=10%) (fI=10%) (fT= 10%) (T=1000 years) = 10  0.1  1  0.1  0.1  0.1  1000 = 1 (one civilization in the Milky Way  us!)

  4. Optimistic Example • Estimated number of technological civilizations present in the Milky Way galaxy: N = (R*=20/year) (fP=50%) (NP=4) (fL=20%) (fI=50%) (fT= 50%) (T=100,000 years) = 20  0.5  4  0.2  0.5  0.5  100,000 = 200,000

  5. Illustration of Drake Equation

  6. Habitable Zones • 1 A.U. = average Earth-Sun distance

  7. Extinction of the Dinosaurs • Possibly caused by impact of a large meteorite • Large amount of dust thrown into atmosphere, causing global cooling, disruption of the food chain • Evidence: • Iridium layer found in fossil record at about time of extinction of dinosaurs • Large numbers of species become extinct at about the same time • Crater in Yucatan may be “the one” • Are extinctions periodic?

  8. Life in the Universe - The Next Step • Assume there is life • Now try to find it! • How? – Depends on the distance & type of life! • Our solar system: can get there, study, probe • Around other stars: • Simple life  need to identify signs • Intelligent life  will send out signs (?)

  9. Finding life on Exoplanets • Problem: Exoplanets are very far away! • Can’t get there • Hard enough to discover the planets themselves • Need to discover something living on them

  10. Green Bank (or Drake) Equation • Estimated number of technological civilizations present in the Milky Way galaxy is given by the average rate of star formation (R*)  fraction of stars having planetary systems (fP)  average number of planets within the habitable zone for various types of star and star system (NP)  fraction of habitable planets that develop life (fL)  fr. of life-bearing planets on which intelligence appears (fI)  fraction of intelligent life forms that develop technology (fT)  average lifetime of a technological civilization (T) • Could be 100 to 1 billion (?)

  11. Homework: Conversions • Convert from hours to years by “multiplying with one” (conversion factors) • x years = y hrs (#years/hrs) = y hrs (#years/days)(#days/hrs) = y hrs (1years/365days)(1day/24hrs) • E.g. 5000 hrs = 5000/365/24 years = 0.57 yr

  12. Fermi Paradox • If ETI exists, it must be widespread • If it’s widespread, why aren’t they among us? • ETI must have had plenty time to occur • Maybe they do not exist • Maybe we didn’t look hard/long enough? • Maybe they are among us?

  13. Signals • Probably electromagnetic waves • Easy to generate • not exceedingly absorbed by interstellar medium, planetary atmospheres • Information can be imprinted on them with minimal energy cost • Travels fast (but not fast enough?!) • We are detectable since 12. December 1901

  14. Time is of the Essence • A lot of things can go wrong in “cosmic instances” like a few thousand years • It is “guesstimated” that a technological civilization might last about 3000 years

  15. SETI • If average lifetime is 1 million years, then the average distance between civilizations in the galaxy is 150 ly • Thus 300 years for messages to go back and forth • Communications via radio signal • Earth has been broadcasting in RF range for most of this century • Earth is brighter than the Sun in radio • 18–21 cm wavelength range good for interstellar communication • SETI search is ongoing • SETI@Home: http://setiathome.ssl.berkeley.edu • If they exist, should we contact them?

  16. SETI with Radio Telescopes • Radio frequencies are used because • Civilizations are likely to use these frequencies • We can observe them from the ground • Biggest radio telescope is in Arecibo, Puerto Rico

  17. CETI – Talking to Aliens • How can we communicate? • Put up a big sign (?!) • Send a (radio) signal • Send a space probe with a message • Should we try to communicate?

  18. Our Messages to the Aliens • Golden plate with essential info on humans • On board Pioneer 10 space probe • Started in the 70’s • past solar system

  19. Our EM Message to the Aliens • In 1974 sent radio signal from Arecibo to globular cluster M13 (300,000 stars, 21,000ly away) • Brighter than the Sun • “The signal, transmitted at 2380 megahertz with a duration of 169 seconds, delivered an effective power of 3 trillion watts, the strongest man-made signal ever sent.”

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