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Longevity of Civilizations

Longevity of Civilizations. ASTR 1420 Lecture 22 from a Nature paper. Drake Equation (Carl Sagan’s version). N = N * × f planet × f E × f life × f intell × f civ × f L. ×. ×. ×. ×. N number of transmitting civilizations. f planet. f Earth. f life. N *. ×. ×. =.

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Longevity of Civilizations

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  1. Longevity of Civilizations ASTR 1420 Lecture 22 from a Nature paper

  2. Drake Equation (Carl Sagan’s version) N = N* × fplanet× fE× flife× fintell× fciv × fL × × × × N number of transmitting civilizations fplanet fEarth flife N* × × = fintell fciv flong N

  3. Delta t argument (Richard Gott 1993, Nature, 363, 315) Lifetime of an event Past Future Tbegin TNow TEnd If there is an End, where do we stand now in the time axis?

  4. Delta t argument (Richard Gott 1993, Nature, 363, 315) Past Future Tbegin TEnd • t will range between 0 and 1. • Calculates a probability of t being in the first or last 2.5%. • Probability of 0.025 ≤ t ≤ 0.975 ? •  95% • At the 95% confidence level, t will NOT be in the beginning 2.5% or in the ending 2.5% range.

  5. Delta t argument (Richard Gott 1993, Nature, 363, 315) • 0.025 ≤ t ≤ 0.975  • Similarly, at the 99% confidence level Past Future Tbegin TEnd

  6. Delta t argument • the length of time something has been observable in the past is a rough measure of its future observability…

  7. History of Human • Homo Sapiens : ≈200,000 years. • 200,000 / 39 < Future < 39*200,000 • 5128 years < Future < 7.8 million years • For our human civilization of 10,000 years • 10,000 / 39 < Future < 39 * 10,000 • 256 years < Future < 390,000 years • Our industrial civilization of ≈200 years • 200 / 39 < Future < 39 * 200 • 5 years < Future < 7,800 years

  8. If aliens are like human 6,400 ≤ N ≤ 9.8 million

  9. SETI Debate

  10. Ernst Mayr • Bioastronomy News (1995, V7, No. 3) • German/American biologist • Harvard Biology Prof. • 7/5/1904 – 2/3/2005

  11. Carl Sagan • Bioastronomy News (1995, V7, No. 4) • We need “functional equivalent of human” not “prevalent humanoids”… • Radio technology  If Aztec civilization survived, would they develop radio technology in several millenia? • We, humanoids, are very young, but we have ~5 billion years to spare in the future. • American Astronomer • Cornell Professor • 11/9/1034 – 12/20/1996

  12. SETI debate Ben Zuckerman Seth Shostak SETI Astronomer • UCLA Astronomy professor

  13. Zuckerman 3 simple postulates have major implications for SETI • after the development of technology, all civilizations will build similar TPF space telescopes • Intelligent life is curious about other life forms • Once they use space telescopes to discover nearby habitable or life-bearing planets, curiosity will lead them to visit these planet • Therefore, SETI program need to look more distant stars!

  14. Shostak • Zuckerman’s argument is only an extended version of Fermi Paradox • Interstellar travel is not as easy as Zuckerman assumes • Also, within 500 light years of us we can only find about a million star systems, so the probability of worlds with intelligent beings is smaller still.

  15. In summary… Important Concepts Important Terms • Delta t argument • Statistical approach to the longevity of civilizations • Logics behind SETI proponent and opponent • UFOs: next class!

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