The Great Silence?

The Great Silence?
Reinventing SETI from the Ground up
Chris McKay
NASA Ames Research Center
cmckay@mail.arc.nasa.gov
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The great silence like the great dryness
Examining the assumptions
Is there anything new to do in SETI?
Can Astrobiology offer insights for SETI?
The Great Silence?
• 1940 Fermi: where are they?
Answer they can’t drive over it’s too far
• 1960 SETI: they are like us so we should hear
them
• 2008 So far silence
• 2025 SETI is growing exponentially
the silence will grow exponentially important
The Great Dryness
The search for life in the Solar System
• 1960 Many possible worlds with life
• 1975 Viking & search for life on Mars - no joy
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Evidence for past water on Mars
Organic matter in Solar System & ISM
Early origin of life on Earth
Ecosystems in extreme environments
Antarctica, deep sea, high temperatures, acid
– ALH84001 purported evidence for life from Mars
• 1997 Astrobiology program created
• 2008 not yet a single further life detection mission
The Copernican Principle
We are typical, if it happened here it is happening elsewhere
• This is not a “physical law” it’s a “rule of thumb”.
– like Bode’s Law or Moore’s Law
– It must therefore yield before detailed analysis
– It may have wide scope but it must certainly fail,
where it fails is of interest
• While it has yet to fail in astronomy it has already failed in
planetary science.
– Earth is unique wrt the planets in our solar system.
– Copernican argument implies life on Earth means life on other worlds.
– Detailed considerations of planetary environments show why this is
not the case.
– This failure of the Copernican Principle is of interest.
• It’s utility in biology is unknown.
Testing the Copernican Principle
(Are we typical?)
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Sunlike stars
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Stars with planets
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Earth-like planets? Coming soon, Kepler Mission
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Origin of life? Search for a second genesis
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Complex life? Look for O2 on distant planets
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Intelligent life?
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Technological intelligent life? SETI
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History of civilization? Read their books
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History of religion? Read their holy books
Creation → Fall → Convent → Redemption → X → Second Coming
Standard SETI Assumptions
about Biology and Culture
• Life arises quickly on a suitable planet
• Life develops intelligence after 3.5 billion years
• Intelligence leads to radio telescopes
• Science and mathematics are universal
(we can share pi with aliens)
The Major Events in the
History of Life on Earth
• Origin of life: 3.8 Gyrs ago
• Multicellular life: 600 Myrs ago
• Intelligent life: 1960’s
Whiggish view of telescope builders
•Steady progress from the origin of life to the telescope
•It take 3.5 Gyr
Evolution of Traits
Convergent
• Flight
• Vision
• Animal intelligence
Anomalous
• Elephant’s trunk
• Peacocks feathers
• Human intelligence
Chances for Intelligence
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All Earth: Dinosaurs (200 million years)
S. America: Terror Birds (25 million years)
Australia: Marsupials (60 million years)
New World: Placentals (60 million years)
Dinosaur Intelligence
Russell, D.A. and R. Seguin 1982.
Reconstructions of the small Cretaceous
Theropod Stenonychosaurus inequalis and
a hypothetical dinosauroid, in Syllogeus
Numer 37, NationalMuseum of Natural
Sciences, Ottawa, Canada.
Conclusion
• Life is likely to be common
• Complex life is likely to be common
• Intelligence may be rare
• Searching is the only way to find out
From the origin of life to SETI
From the origin of life to SETI
Time for intelligence on other worlds
McKay, C.P. 1996 Time for intelligence on other planets. In
``Circumstellar Habitable Zones", Edited by L.R. Doyle
In principle radio telescopes could have been build on an
inhabitable planet ~100 Myr after formation.
Due to:
Smaller layer of water
No plate tectonics
Loss of H2
Mars may have had is
Cambrian explosion after
100 Myr rather than 3 Gyr,
radio telescopes 3 Myr later.
So what about the Great Silence?
• Continue searching
• New ideas:
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They came and they went, look for relics
Look for beacons not signals
Look in the laws of physics
Look in DNA
Possible and Improbable Relics
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Dark Matter
Dark Energy
Fine tuning of physical laws
Life
Neon depletion in planets
Absence of anti-matter
How can we make the case that any of these is an
artifact?
Ultimate implications of silence
• The Copernican Principle fails at the level
of human intelligence.
• The universe may be full of life but it is
not full of intelligence.
• If the laws of physics were tuned by
intelligence we did it in the future.