Lecture 38. The Fermi Paradox, Von Neumann Machines, Galactic Colonization.

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Lecture 38. The Fermi Paradox, Von Neumann
Machines, Galactic Colonization.
reading Chapter 13
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Enrico Fermi
Built the first nuclear reactor (under Stagg
Field at the University fo Chicago), demonstrated
the concept of the nuclear chain reaction in
1942. 1938 Novel Prize in Physics for work on
induced radioactivity.
When he submitted his famous paper on beta decay
to the prestigious journal Nature, the journal's
editor turned it down because "it contained
speculations which were too remote from reality".
Thus, Fermi saw the theory published in Italian
and in German before it was published in
English. He never forgot this experience of being
ahead of his time, and used to tell his protégés
"Never be first try to be second".
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The Fermi Paradox
First articulated by Enrico Fermi in 1950. If
there is a high possibility for ETL 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. Why
would robots be better to use than humans for
this task??
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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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Von Neumann Machines and SETI
So, if there arent Von Neumann Machines all over
the universe, we must be alone. Therefore, is
SETI a waste of time/money???
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How Likely Is It That We Are First?
Intelligent civilization on Earth has only
been around for 4,000 years/3.8 Ga. Perhaps it
takes 4.5 Ga to evolve intelligent
civilizations. Suppose intelligence arises
around 1/1 million stars. Given 100 billion stars
in the galaxy, 100,000 should evolve
civilizations. If the first of these arose 6 Ga
(age of the solar system 4.5 Ga) then an
intelligent civilization should be arising
somewhere in the galaxy every 60,000 years. (If
you use 1/1 billion stars, then you expect 100
civilizations, or one arising every 60 million
years).
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How Likely Is It That We Are First?
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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. If you travel at 0.01 c,
and it takes 5,000 years between hops it would
only take 100 million years to colonize the
entire galaxy.
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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
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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.
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Lecture 39. Does Life Elsewhere Seem Likely?  The
Psychological Impact of Finding Life Elsewhere.
reading Chapter 14