Longevity of Civilizations

ASTR 1420

Lecture 22

from a Nature paper

SETI Debate

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

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

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.

Delta t argument (Richard Gott 1993, Nature, 363, 315)

Tbegin TEnd

Past Future

• 0.025 ≤ t ≤ 0.975

• Similarly, at the 99% confidence level

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!

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

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

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!

SETIWill it succeed?

ASTR 1420

Section 12.2 +

?

Ernst Mayr• Bioastronomy News (1995, V7, No. 3)

• German/American biologist• Harvard Biology Prof.• 7/5/1904 – 2/3/2005

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

SETI debate

Ben Zuckerman• UCLA Astronomy professor

Seth Shostak• SETI Astronomer

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

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