The Fermi Paradox

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The Fermi Paradox
First articulated by Enrico Fermi in 1950. If
there is a high possibility for ETL (extra
terrestrial life) then where is
everybody??? Given -planets (protoplanetary
disks) are common -life originated early on
Earth, is easy to evolve -only a matter of time
before intelligence arises -the vastness of the
universe 100 billion stars in the Milky Way
galaxy 100 billion galaxies in the universe -the
tremendous age of the universe Then -expect to
have a large number of civilizations. It is only
a matter of time before they develop the ability
for intergalactic travel.
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The Fermi Paradox, cont.
However there is no evidence of galactic
colonization. Herein lies the paradox. Maybe
we are the first? We have already built robots
to travel to other planets in the
solar system. It is reasonable that we will keep
building better robots for exploration of our
solar system. It didnt take a great deal of
technology to land on the Moon. We (beings)
dont have to colonize - machines we construct
could do the job.
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Von Neumann Machines
Self-replicating machines. Travel to and explore
other worlds. Dig up resources. Use those
resources to build more robots. Disseminate and
colonize additional worlds. Would spread from
star system to star system. Requires technology
only slightly more advanced than our own.
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Extension of the Fermi Paradox
In 1981, Frank Tipler used the idea of
colonization by self-replicating Von Neumann
machines to argue that machines would spread
throughout the galaxy as soon as any
civilization reaches a level to build these
machines. Because it doesnt take much more
technological capability than what we already
have. And if civilizations are common. The
universe should be overrun by self-replicating
machines.
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How Likely Is It That We Are First?
Suppose intelligence arises around 1 in one
million stars. Age of galaxy 12 billion
years but you have to wait a few billion
years For a sufficient number of supernova to
deliver heavy elements To the galaxy. Indeed,
this is borne out by observations of
planetary Systems around nearby stars Given 100
billion stars in the galaxy, 100,000 should
evolve civilizations. If the first of these
arose 6 Ga then an intelligent civilization
should be arising somewhere in the galaxy every
60,000 years.
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How Long Would It Take To Colonize The Galaxy?
If -you could travel at 10 the speed of light,
0.1 c (3 x 107 m/sec) And The average distance
between stars is 5 light years (50
years) And After 150 years you can spread to
the next system, sending new craft to one or two
other systems. Then You could colonize the
entire galaxy in 10 million years if you start at
the edge of the galaxy.
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One day, some civilization decides to use its
resources to launch 1000 inhabited space ships in
random directions.   Each spaceship is capable
of a propulsion velocity of 0.1 c.   99 of all
spaceships are destroyed before reaching another
planet   Upon arriving at another planet, on
average 10,000 years later, the surviving members
of the civilization spend 10,000 more years on
that planet converting its resources into 1000
more spaceships to repeat this exercise.
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Galactic Colonization, cont.
Would other civilizations want to colonize? Right
now we have no motivation - the costs outweigh
the need. However, the human desire for
colonization is strong - filling every
niche. Reasons for colonization - escape
war - escape persecution - lack of resources -
too much competition for resources - protect
your lineage/civilization from extinction Stupid
Civilizations cant colonize because they use up
all their resources first
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Possible Solutions to the Fermi Paradox

• We are alone / we are the first / there is no
  galactic
• civilization.
• Civilizations are common, but no one has
  colonized the galaxy.
• Why?
• - technological difficulties - interstellar
  travel is difficult or
• vastly more expensive or dangerous than we
  think
• - maybe our desire to explore is unusual and
  other societies
• would not choose to leave their stars
• - maybe civilizations tend to destroy themselves
• There is a galactic civilization and it is
  deliberately avoiding
• us / hiding their existence from us / or we just
  havent found
• them yet (havent looked at enough stars??)

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The Prime Directive / The Zoo Hypothesis
Other civilizations are aware of our presence,
but they have deliberately kept us in the dark
about their existence. Or they have kept our
solar system off limits to leave us
alone. The Sentinel Hypothesis The monolith
in Arthur C. Clarkes 2001 A Space Odyssey ETs
leave a device that sends a signal when our
civilization becomes sophisticated enough.