Are We Alone? Dreams of Life Elsewhere

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Austin Boyd
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1 Are We Alone? Dreams of Life Elsewhere

2 Where is everybody? Fermi s paradox (1950 lunch conversation) Assume 3 levels of extraterrestrial civilizations ETC1, like ours (energy resources of a planet) ETC2, more powerful than ours (energy of a star) ETC3, even more powerful (energy of a galaxy) From ETC1, assume life expands to fill all available space, so that ETC2 and ETC2 would seek to colonize galaxies Thus Milky Way should be swarming with life Where are they? The lemming paradox Lemmings produce 3 litters/yr, 8 offspring/litter Earth should be swarming with lemmings Where are they?

3 Prehistory of Fermi s paradox Are we alone - a deep, myth-driving question Modern science assumes universality of physical AND biological laws Empirical verification of life elsewhere seems difficult Issues at stake in the debates Assumptions about order and universality Limits of science Definitions of life and intelligence Assumptions about how life behaves once it emerges

4 Plurality of worlds before 1700 Greek atomists versus Aristotle Lucretius, -55: Granted, then, that empty space extends without limit it is highly unlikely that this earth and sky is the only one to have been created and that all those particles are accomplishing nothing. This follows from the fact that our world has been made by the spontaneous congregation and coalescence of atoms whose suddenly formed combinations could serve to produce earth, sea, sky, and the races of living creatures. Medieval Christians versus Aristotle Copernican cosmology legitimates pluralism Giordano Bruno s On the infinite universe and worlds, 1584 Kepler s Dream, 1609 (publ. 1634), life on Moon Descartes cautious pluralism of many solar systems Fontenelle s Conversations on the plurality of worlds, 1686, life on Venus and Jupiter, also around all Suns

5 Newtonian legacies Newton almost silent on plurality Shifts natural theology to multiple worlds 19c debates religious and philosophical Purpose of vast expanses of space? Can Christian doctrine of redemption be reconciled with plurality of worlds? Anthropocentrism of German idealists Literary invention of aliens H.G. Wells, War of the Worlds, 1897, monster Martians Science fiction takes off as a genre after 1900

6 Astrophysical foundations for modern ETC debates Darwinian evolution & origin of life Stellar spectroscopy confirms chemical uniformity of stars Refined nebular hypothesis & formation of solar systems Planetary science of Mars, Earth s nearest neighbor

7 Seeking life on Mars Schiaparelli s canali mapped in 1877 Percival Lowell s popularization, 1890s Mapped canals, vegetation, polar ice caps Geological theory of planets Non-reproducible results and optical illusion of the lines tainted planetary astronomy for decades! Yet spectroscopy and infrared astronomy of s found conditions on Mars suitable for earth-like life

8 Mars cont--viking landers, 1976 Pro-life findings Evidence of liquid water (erosion) Earth-like abundances of chemical elements in soil and atmosphere Positive results in nutrient experiments Anti-life findings No organic molecules (except water, CO 2 ) Non-biological explanations for nutrient experiments No known terrestrial organisms could survive in current Martian conditions

9 Viking results View from Viking 1 Mars runoff channel, 400 km Red River, LA, 300 km

10 Extra-solar planets? Laplace s nebular hypothesis, 1800 J. Jeans tidal ejection hypothesis, 1916 von Weizsäcker s nebular hypothesis, 1944 Search for extra-solar planets, 1960s Wobble in radial or transverse star velocities? Star brightness varies in edge-on transits? Stars with slowed rates of rotation? Direct observation (April 2005)? Ca. 150 planetary systems found, but not earth-like Mostly large gaseous planets like Jupiter (no surface!) Most orbits very close to star (< 1 AU) and very eccentric Biased by current observing techniques?

11 From planets to life? Amino acids and 4 nucleotides (A,G,T,C) in all earth life implies common origin Urey-Miller experiment, 1953 Water+amonia+methane+hydrogen = amino acids Conditions required for earthlike life Suitable atoms for carbon chemistry (or silicon?) Liquid solvents (water or thick atmosphere) Moderate temperatures Long time periods of stability (1 billion yrs?) Did RNA come first? Problem of ribose phosphate chain Non-earthlike life? Must reproduce, interact with environment, evolve, go intelligent?

12 Snythesizing amino acids

13 The Drake Equation, 1960 New stars/yr in Milky Way (R) Fraction of Sun-like planets Fraction of Earth-like planets Fraction of Earths where life starts Fraction of life-planets that survive Fraction of life that goes intelligent Length of average lifetime of ETC (L) Drake s equation: Number of intelligent ETCs now = R x f S x f E x f L x F s x F i x L = L Is this an equation or a framework for discussion?

14 Where are they? SETI Did life in the solar system begin on Mars? Space travel or little green men Negative results to date? At 50 km/s, would take 50,000 yrs for round-trip to nearest Sun-like star, Alpha Centauri Clearly need more exotic travel technologies we have now Radio communication and SETI Search frequencies near 21 cm hydrogen line ( quiet part of spectrum where galactic static is minimal) Radio telescope searches since 1960s NASA-funded search, SETI@home since 1999 ( using data from Arecibo, PR radio telescope They re still not there!

Astrobiology: The Semester in Review

A Universe of Life Astrobiology: The Semester in Review Honors 228 with Dr. Harold Geller Searching for life everywhere Planets, stars, galaxies, Big Bang Conception of size and distance Stars and the