Announcements

1
Announcements

• No HW this week (Q4)
• HW12 due on Friday, December 16
• No class on Tuesday, December 13
• Thursday schedule on Tuesday, December 13 (in
  lieu of Thanksgiving day) TA has office hours
• Final on Thursday, December 22, 1100?130, in
  Harriman 137

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Search for Life in the Universe

• Chapters 12 (Part 2) 13
• Alien Civilizations

3
Outline

• UFOs
• Crashed Aliens in Roswell, NM
• Crop Circles, Abductions, etc.
• Ancient Visitations
• Cover-Up Scientific Disinterest
• Where Is Everybody?
• Age of Civilization
• Cosmic Calendar
• Civilization Timescales
• Youngest Civilization
• Galactic Colonization
• Colonization Models
• Motives for/against Colonization
• Possible Solutions to the Paradox

4
UFOs

• Appearance
• Jet planes first introduced at the end of World
  War II ? public aware of fast-moving aircrafts
• First UFO claim in June 1947
• Flew erratic, like a saucer ? flying saucer
• 50 of the public believe in the existence of
  UFOs
• Air Force Investigation
• 20-year investigation
• 90 of claims discarded
• Remaining 10 indeterminate
• Lack of proof is no proof

5
Crashed Aliens in Roswell, NM

• Known facts
• Rancher found crash remnants July 1947
• Military personnel picked up the debris
• Remains shown next day in Fort Worth, TX
• Claimed to be remains of a weather balloon
• Claims by Stanton Friedman (1978)
• Crash an alien spacecraft
• Alien bodies also recovered
• Story hushed up by military
• Analysis
• Project Mogul balloon used for secret monitoring
  of Soviet tests
• Witness accounts in seventies contradicted or
  discounted
• Motive for secrecy not clear
• Ability to keep secret highly doubtful

6
Crop Circles, Abductions, etc.

• Crop circles
• Claim too accurate and too quick to be done by
  humans
• Shown to be possible
• Some admitted to be pranks
• Abductions
• Sleep paralysis common dream during rapid eye
  movement (REM)
• Also known during day dreaming

7
Ancient Visitations

• Ancient drawings
• Claim pictures of aliens
• Counterclaim other possibilities abound
• Nazca markings
• Claim needed unavailable knowledge
• Counterclaim did not need unavailable knowledge
• Claim could only be seen from space
• Counterclaim could be form of worship
• Egyptian pyramids
• Claim Egyptians could not build the pyramids by
  themselves
• Counterclaim it was shown that the pyramids
  could be constructed with tools available then

8
Cover-Up Scientific Disinterest

• Cover-up
• Motive to avoid alarm 50 already think that
  aliens have landed
• U.S. Government notoriously unable to keep
  secrets known by many for a long time
• All other governments need to participate in the
  conspiracy
• Scientific disinterest
• Stems from lack of evidence, not disinterest
• If there was serious evidence, or the chance to
  obtain serious evidence, scientists would jump at
  it

9
Where Is Everybody?

• Statement of the Paradox
• If our civilization is not unique, others would
  have formed long before us, would now be far more
  advanced, and would long have colonized the
  Galaxy
• Where are they?
• Von Neumann machines
• Self replicating robots
• Overcome distance by much longer longevity
• Frank Tipler Von Neumann machines would by now
  have colonized the entire Galaxy
• We have seen no evidence ? our civilization is
  unique

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Cosmic Calendar
11
Civilization Timescales

• Time to form a civilization done by us in 4.6
  byr
• Age of Galaxy 10 byr
• Time to form civilizations before us 6 byr
• Rate
• 1011 stars x 10?6 probability 105 civilizations
  1 per 6 x 104 yr
• 1011 stars x 10?6 probability / 20 (heavy element
  abundance) 5,000 civilizations 1 per 105 yr
• 1011 stars x 10?9 probability 100 civilizations
  1 per 6 x 107 yr

12
Youngest Civilization

• Assume youngest civilization 105 years older than
  us
• At a distance of 8 x 104 ly, we would still see
  it at an age of 2 x 104 yr

13
Colonization Models

• Light travel time through the Galaxy
• 105 yr
• Nuclear-powered travel at 0.1c
• 106 yr
• Coral Model (0.1c)
• Colonize a star and then move on
• Add 150 yr per step of 50 yr
• Multiplies expansion time by 4

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Motives for/against Colonization

• For
• Human nature
• Humankind spread quickly
• And then spread more by displacing other people
• Against
• Population growth too expensive
• Conquering a backward civilization not worth
  defeating cavemen, although natural resources
  may be valuable
• Conquering a more advanced civilization
  cavemen unlikely to defeat us

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Possible Solutions to the Paradox

• We are alone
• The numbers in the Drake equation are poorly
  known, so we are possibly alone
• Civilizations but no colonization
• Technical difficulties our estimates may be too
  optimistic
• Sociological reasons population and energy
  problems solved another way
• Self destruction we have already come close to
  nuclear confrontation
• There is a Galactic civilization
• They are keeping us in a nature reserve
• We are not interesting
• We may be interesting sometime in the future,
  when our action manifests our cosmic maturity

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Thank you for your attention

• Good luck on the final
• Thursday, December 22, 1100?130
• in Harriman 137 (here)