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Longevity of Civilizations
ASTR 1420
Lecture 22
from a Nature paper
SETI Debate
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Drake Equation (Carl Sagan’s version)
N number of transmitting civilizations
N = N* × fplanet × fE × flife × fintell × fciv × fL
× × × ×
× × =
N
N* fplanet fEarth flife
fintell fciv flong
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Δt argument (Richard Gott 1993, Nature, 363, 315)
Tbegin TEnd
Past Future
If there is an End, where do we stand now in the time axis?
TNow
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Delta t argument (Richard Gott 1993, Nature, 363, 315)
Tbegin TEnd
Past Future
• 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.
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Delta t argument (Richard Gott 1993, Nature, 363, 315)
Tbegin TEnd
Past Future
• 0.025 ≤ t ≤ 0.975
• Similarly, at the 99% confidence level
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Delta t argument
• the length of time something has been observable in the past is a rough measure of its future observability…
At 95% confidence!
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History of Human• Homo Sapiens : ≈200,000 years.
o 200,000 / 39 < Future < 39*200,0005128 years < Future < 7.8 million years
• For our human civilization of 10,000 years
o 10,000 / 39 < Future < 39 * 10,000256 years < Future < 390,000 years
• Our industrial civilization of ≈200 yearso 200 / 39 < Future < 39 * 2005 years < Future < 7,800 years
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If aliens are like human
6,400 ≤ N ≤ 9.8 million
R* 20 stars/yr
fplanet 1
nE 0.5
flife 0.5
fintell 0.5
fciv 0.5
L 5100 yrs
R* 20 stars/yr
fplanet 1
nE 0.5
flife 0.5
fintell 0.5
fciv 0.5
L 7.8 million yrs
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In summary…
Important Concepts• Delta t argument
• Statistical approach to the longevity of civilizations
Important Terms
Chapter/sections covered in this lecture : Longevity of CivilizationUFOs : next class!
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SETIWill it succeed?
ASTR 1420
Section 12.2 +
?
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Ernst Mayr• Bioastronomy News (1995, V7, No. 3)
• German/American biologist• Harvard Biology Prof.• 7/5/1904 – 2/3/2005
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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
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SETI debate
Ben Zuckerman• UCLA Astronomy professor
Seth Shostak• SETI Astronomer
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Drake Equation (Carl Sagan’s version)
N number of transmitting civilizations
N = N* × fplanet × fE × flife × fintell × fciv × fL
× × × ×
× × =
N
N* fplanet fEarth flife
fintell fciv flong
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In summary…
Important Concepts• Logics behind each SETI argumentso Mayr vs. Sagano Zuckerman vs. Shostak
• Statistical approach to the longevity of civilizations
Important Terms
Chapter/sections covered in this lecture : SETI debate