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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, 11:00 1:30, in Harriman 137.

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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, 11:001:30, in Harriman 137

AST 248, Fall 2005


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Search for Life in the Universe

Chapters 12 (Part 2) & 13

Alien Civilizations

AST 248, Fall 2005


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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

AST 248, Fall 2005


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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

AST 248, Fall 2005


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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

AST 248, Fall 2005


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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

AST 248, Fall 2005


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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

AST 248, Fall 2005


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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

AST 248, Fall 2005


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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

AST 248, Fall 2005


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Cosmic Calendar

AST 248, Fall 2005


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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

AST 248, Fall 2005


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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

AST 248, Fall 2005


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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

AST 248, Fall 2005


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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

AST 248, Fall 2005



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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”

AST 248, Fall 2005


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Thank you for your attention

Good luck on the final:

Thursday, December 22, 11:001:30

in Harriman 137 (here)

AST 248, Fall 2005


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