Transcript Is there anybody out there?

A Dale Mabry Journal Club Presentation
Intelligent Life: Rare Event or
Common Occurrence?
Life - as we know it
Life needs
• RNA
• AminoAcids
• Water (fluid)
Life shows
• Cellular organization
• Inheritance/Reproduction
• Metabolism
smoker video
• Even if bacterial life is relatively
common, the main question is, do we
share the Universe with intelligent life?
• “After all, Captain Kirk goes boldly
where no humanoid went before NOT to
search for new strains of bacteria or a
moss”. (Shostak)
• Shostak’s main argument is that
intelligent life will evolve as the result
of competition and natural selection
among higher forms of life.
Bacteria
Metazoa
Intelligent lifeforms
200-300 million
An attempt to calculate the likelihood of alien life in the galaxy
Result?
Hundreds or thousands of potential civilizations
VeryLargeArray
The endeavor (SETI) is a
yes-or no-experiment. The
search is a
failure, until it suddenly
becomes a success.
(Shostak)
[email protected]
Pioneer 10 Plague
Location!!!!
Critical Issues
• Position of star in the galaxy
• Lifetime and size of the star (habitable
zones and timeframes)
• Planet with metals and large moon
• Large planets in the star system
• Several billion years without destruction
• Limited amount of global mass
extinctions
Drake’s Equation Revisited
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N* = stars in the Milky Way galaxy --> 200 to 300 million
fp = fraction of stars with planets --> 5-6%
fpm = fraction of metal-rich planets --> less than 1%
ne = planets in a stars habitable zone --> 1
ng = stars in a galactic habitable zone
fi = fraction of habitable planets where life does arise
• fc = fraction of planets where complex metazoans arise
• fl = percentage of a lifetime of a planet that is marked by the
presence of complex metazoans
• fm = fraction of planets with a large moon
• fj = fraction of solar systems with Jupiter sized planets
• fme = Fraction of planets with critically low number of mass
extinction events
Summary
There is mounting agreement and
evidence supporting the potential for an
abundance of bacterial life.
Summary
“Intelligent” higher forms of life are
either also abundant because they will
inevitably evolve from bacterial life…
Summary
…or higher forms of life are very rare
(perhaps unique on earth) because the
odds are heavily stacked against their
appearance.