Life in the Universe

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Life in the Universe

• Joseph Busche

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• Introduction
• Earth the only place where life is known to
  exist
• Characteristics of Life on Earth
• Origin of Life local or from the stars?
• Extraterrestrial Life
• Drake Equation
• Fermi Paradox
• Conclusions

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What is Life?

• life the form of existence that distinguishes
  living organisms from dead organisms or inanimate
  matter in the ability to carry on metabolism,
  respond to stimuli, reproduce, and grow
  Websters
• Definition is circular, vague, and limited
• Necessarily our conception of life is heavily
  influenced by that around us

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Earth

• Formed approximately 4.5 billion yrs ago
• Oldest traces of organic matter - 3.8 billion yrs
  ago
• Oldest fossils 3.5 billion yrs ago
• Eukaryotes (cells with nuclei) 2 billion yrs
  ago
• Cambrian explosion 500 million yrs ago
• Dinosaur extinction 65 million yrs ago
• Modern Human 100,000 yrs ago

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Characteristics of Earth Life

• Carbon based organic chemistry
• Water necessary for life as we know it
• Exists in an extreme variety of environments
  (even volcanic vents)
• Millions of species currently
• Average life of a species approx 1 million yrs
• Most species are extinct (some estimates are as
  high as 97-98)

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Origin of Life the Stars?

• Panspermia the idea that life (or its building
  blocks) originated in space and seeded the young
  earth
• Astronomers have found many complex organic
  molecules in clouds similar to the one that
  formed our solar system
• Laboratory experiments indicate that complex
  chemistry takes place on interstellar dust grains
• Idea is not favored by most scientists

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Origin of Life home grown?

• Miller-Urey experiments
• Simulate early earth conditions (water, hydrogen,
  methane, ammonia prominent in the atmosphere)
• Electric spark to induce chemical reactions
• At the end of one week, a variety of organic
  molecules including 5 amino acids were found
• Extensions of the experiment showed that
  proteinoids and ATP can be formed

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Extraterrestrial (ET) life

• An ET does not have to be intelligent
• Life may be common, but intelligent life may not
• Simplest thing to do is to look for life after
  the pattern seen on Earth
• Candidates in our solar system include Mars and
  Europa (some include other moons of Jupiter and
  Saturns moon Titan)

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Drake Equation (1961)

• Most popular approach to guesstimate how common
  life might be
• With such a large number of stars in the galaxy
  (100 billion), even if life were rare we might
  not be alone
• The equation has many forms, but the basic idea
  is the same in all of them

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NNfpnefl fi fc fL
We can think of this equation as a series of
questions? 1.) How many stars are there in the
galaxy (N)? 2.) What fraction of those stars
have planets (fp)? 3.) If a star has planets, how
many are capable of supporting life (ne)? 4.) On
what fraction of those planets did life evolve
(fl)? 5.) On what fraction of life planets does
intelligence evolve (fi)? 6.) What fraction of
intelligent species have the means and desire to
communicate (fc)? 7.) What fraction of a planets
life will a communicating life form survive (fL)?
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What numbers should be used?

• N - this number is pretty well established to be
  about 100 billion.
• fp recent data and theoretical models indicate
  that planets are common
• Optimistic guess (99)
• Pessimistic guess (20)

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Number of life suitable objects

• ne in our own solar system there are
  conceivable 3 or 4 habitable bodies in what is
  known as the life zone (earth, mars, venus, and
  possibly a moon of jupiter)
• Optimistic guess (3)
• Pessimistic guess (1/10)

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How likely is it for life to develop?

• Very little data
• Biochemistry suggests that life will arise where
  conditions support it
• Planetary geology may indicate that conditions
  for life are not rare
• Optimistic guess (1/2)
• Pessimistic guess (0.0001)

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How likely is intelligence to develop?

• Are dolphins, birds, monkeys intelligent?
• Evolution is NOT goal oriented (i.e. it has no
  purpose)
• Simpler life forms are more successful
• Intelligence may be useful for survival in rare
  circumstances
• Optimistic guess (0.0001)
• Pessimistic guess (1 out of a billion)

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How many develop technology?

• WHO KNOWS????????
• Will intelligent species left to themselves
  eventually develop a technology sufficient for
  interstellar communication?
• Optimistic guess (1)
• Pessimistic guess (0.1)

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How long will a technological species survive?

• The earth is 4.5 billion yrs old
• Humans survived as a communicating civilization
  for about 100 yrs
• This implies fl is 0.00000001 (10-8)
• If we last as long as the dinosaurs did wed get
  fl is 0.02

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Results

• Optimistically there are 300,000 civilizations
  this is almost certainly absurdly large because
  that means that one is probably quite close to
  us
• Pessimistically there are 10-13 civilizations
  this seems absurdly small because it implies
  that we are a very lucky accident
• My own numbers led to 25 civilizations

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Fermis Paradox (1950?)

• In a lunchtime discussion of life in the
  Universe, Fermi remarked that if intelligent life
  is common, then where are they!
• Flippant as it sounds, it is an important
  question that does not get the press that it
  deserves
• This approach leads to a pessimistic view about
  intelligent life in the Universe

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Geometric Growth

• How long would it take to get a million dollars
  if you start with a penny and double it every
  day? Answer less than a month!
• If a species started colonizing the galaxy how
  long would it take to complete the process?

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Use ourselves as an example

• How long will it take before we colonize another
  star system?
• Lets guess 10,000 years
• If the number of new systems colonized doubles
  every 10,000 years, how long will it take to
  colonize the whole galaxy?
• It would take about 36 colonization waves
• This implies it would take only 360,000 years!

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Analysis

• Colonization is more difficult than sending
  probes or radio signals
• Even if the colonization time is 1 million years,
  that still isnt a long time
• If at ANY time in the past 10 billion years a
  species started a colonization process it would
  probably be here
• Conclusion ????