Transcript Integrative Studies 410 Our Place in the Universe

Final Exam
• Comprehensive
– Most questions from Ch. 15-18, some from Ch. 4-14,
few from Ch. E-3
• Multiple choice plus few short answer questions
• Please study:
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Midterm exams (available on homepage)
Homework
Activities
Textbook
Powerpoint slides
Green Bank (or Drake) Equation
• Estimated number of technological civilizations present in
the Milky Way galaxy is given by
the average rate of star formation (R*)
 fraction of stars having planetary systems (fP)
 average number of planets within the habitable zone for
various types of star and star system (NP)
 fraction of habitable planets that develop life (fL)
 fr. of life-bearing planets on which intelligence appears (fI)
 fraction of intelligent life forms that develop technology (fT)
 average lifetime of a technological civilization (T)
• Could be 100 to 1 billion (?)
Pessimistic Example
• Estimated number of technological civilizations
present in the Milky Way galaxy:
N = (R*=10/year)
 (fP=10%)
 (NP=1)
 (fL=10%)
 (fI=10%)
 (fT= 10%)
 (T=1000 years)
= 10  0.1  1  0.1  0.1  0.1  1000
= 1 (one civilization in the Milky Way  us!)
Optimistic Example
• Estimated number of technological civilizations
present in the Milky Way galaxy:
N = (R*=20/year)
 (fP=50%)
 (NP=4)
 (fL=20%)
 (fI=50%)
 (fT= 50%)
 (T=100,000 years)
= 20  0.5  4  0.2 
= 200,000
0.5 
0.5 
100,000
Illustration of Drake Equation
Habitable Zones
• 1 A.U. = average Earth-Sun distance
Extinction of the
Dinosaurs
• Possibly caused by impact of
a large meteorite
– Large amount of dust thrown into atmosphere,
causing global cooling, disruption of the food chain
– Evidence:
• Iridium layer found in fossil record at about time of
extinction of dinosaurs
• Large numbers of species become extinct at about the same
time
• Crater in Yucatan may be “the one”
• Are extinctions periodic?
Life in the Universe - The Next Step
• Assume there is life
• Now try to find it!
• How? – Depends on the distance & type of
life!
– Our solar system: can get there, study, probe
– Around other stars:
• Simple life  need to identify signs
• Intelligent life  will send out signs (?)
Finding life on Exoplanets
• Problem: Exoplanets are very far away!
– Can’t get there
– Hard enough to discover the planets themselves
– Need to discover something living on them
Green Bank (or Drake) Equation
• Estimated number of technological civilizations present in
the Milky Way galaxy is given by
the average rate of star formation (R*)
 fraction of stars having planetary systems (fP)
 average number of planets within the habitable zone for
various types of star and star system (NP)
 fraction of habitable planets that develop life (fL)
 fr. of life-bearing planets on which intelligence appears (fI)
 fraction of intelligent life forms that develop technology (fT)
 average lifetime of a technological civilization (T)
• Could be 100 to 1 billion (?)
Homework: Conversions
• Convert from hours to years by “multiplying
with one” (conversion factors)
• x years = y hrs (#years/hrs)
= y hrs (#years/days)(#days/hrs)
= y hrs (1years/365days)(1day/24hrs)
• E.g. 5000 hrs = 5000/365/24 years = 0.57 yr
Fermi Paradox
• If ETI exists, it must be widespread
• If it’s widespread, why aren’t they among
us?
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ETI must have had plenty time to occur
Maybe they do not exist
Maybe we didn’t look hard/long enough?
Maybe they are among us?
Signals
• Probably electromagnetic waves
– Easy to generate
– not exceedingly absorbed by interstellar
medium, planetary atmospheres
– Information can be imprinted on them with
minimal energy cost
• Travels fast (but not fast enough?!)
• We are detectable since 12. December 1901
Time is of the Essence
• A lot of things can go wrong in
“cosmic instances” like a few
thousand years
• It is “guesstimated” that a
technological civilization might last
about 3000 years
SETI
• If average lifetime is 1 million years, then the average
distance between civilizations in the galaxy is 150 ly
– Thus 300 years for messages to go back and forth
• Communications via radio signal
– Earth has been broadcasting in RF range for most of this
century
– Earth is brighter than the Sun in radio
– 18–21 cm wavelength range good for interstellar
communication
• SETI search is ongoing
– SETI@Home:
http://setiathome.ssl.berkeley.edu
• If they exist, should we contact them?
SETI with Radio Telescopes
• Radio frequencies are used because
– Civilizations are likely to use these frequencies
– We can observe them from the ground
• Biggest radio telescope is in Arecibo, Puerto
Rico
CETI – Talking to Aliens
• How can we communicate?
– Put up a big sign (?!)
– Send a (radio) signal
– Send a space probe with a message
• Should we try to communicate?
Our Messages to the Aliens
• Golden plate
with essential
info on
humans
• On board
Pioneer 10
space probe
• Started in the
70’s
• past solar
system
In 1974 sent radio
signal from Arecibo
to globular cluster
M13 (300,000 stars,
21,000ly away)
Brighter than the Sun
“The signal, transmitted
at 2380 megahertz with a
duration of 169 seconds,
delivered an effective
power of 3 trillion watts,
the strongest man-made
signal ever sent.”
Our EM Message to the
Aliens