REMINDERS

• Final homework due Wednesday

• Final Exam Thursday next

• Office hours Wednesday, 2-3 PM

• No class Tomorrow!

Wednesday, August 13, 2014 LIFE IN THE

Wednesday, August 13, 2014 THE SEARCH FOR LIFE

• are seeking to answer one of the oldest questions humanity has posed: are we alone in the universe?

• This question has taken several forms throughout the years, even requiring an investigation of what is meant by ‘life’

• The search is active today and is responsible for several areas of research

Wednesday, August 13, 2014 SETI

• The Search for Extra- Terrestrial Intelligence (SETI) is the name given to the several different active searches for intelligent alien life around the world

• Includes search for signals from extraterrestrial civilizations and also evidence of advanced (modification of environment) Wednesday, August 13, 2014 CLASS ACTION!

Wednesday, August 13, 2014 WHICH ENVIRONMENTAL FACTOR BELOW IS MOST IMPORTANT FOR LIFE?

• (A)

• (B) Protection from radiation

• (C) Moderate average temperatures

• (D) Good restaurants

Wednesday, August 13, 2014 WHICH ENVIRONMENTAL FACTOR BELOW IS MOST IMPORTANT FOR LIFE?

• (A) Oxygen

• (B) Protection from radiation

• (C) Moderate average temperatures

• (D) Good restaurants

Wednesday, August 13, 2014 CONDITIONS FOR LIFE

• Assuming that we’re looking for life as we know it (-like life), there are several environmental conditions necessary:

• Stable in temperature

• Moderate atmospheric pressure

• Liquid water

• Sources of

Wednesday, August 13, 2014 MILLER-UREY EXPERIMENT

• Tried to recreate the environment on the early Earth to investigate the origin of life

• Was able to produce dozens of amino acids (the building blocks of DNA and life) in the closed system

Wednesday, August 13, 2014 HABITABLE ZONE

• The region around a where can have environments suitable for life

• There is still some debate as to exactly how big this region can be around different types of

• Temperature is the main factor:

• closer = hotter farther = cooler middle = just right

Wednesday, August 13, 2014 HABITABLE ZONE

Wednesday, August 13, 2014 HABITABLE ZONE

Wednesday, August 13, 2014 HABITABLE PLANETS

• Must have:

• Average temperature range between freezing and boiling points of water

• Liquid water on surface

• Plenty of chemical elements and molecules

• Source of energy (for example: the )

Wednesday, August 13, 2014 HABITABLE PLANETS

• Probably have:

• Active geologic system (volcanoes, plate tectonics, etc.)

• Not too high or low a surface gravity

• Moderate atmospheric pressure (though oxygen is not necessary)

• A moderately fast rotation rate (not tidally locked)

Wednesday, August 13, 2014 HABITABLE PLANETS

• Might have:

• A large Moon (which creates tides)

• Salty

• Mass between 0.5 and 5.0 Earth masses

• Complex organic molecules

Wednesday, August 13, 2014 KNOWN PLANETS

Wednesday, August 13, 2014 HABITABLE PLANETS

Wednesday, August 13, 2014 CLASS ACTION!

Wednesday, August 13, 2014 EVEN IF THE LIFE ON A IS ONLY MICROBES, IT WILL STILL PRODUCE OBSERVABLE SIGNATURES

• What might be the most easily detectable and unmistakable of these signatures?

• (A) Exotic atmospheric compositions (ozone, methane, etc.) that can only be formed by life

• (B) Phosphorescent light from bioluminescence

• (C) Changes in the planet’s atmosphere and surface

• (D) Good restaurants

Wednesday, August 13, 2014 EVEN IF THE LIFE ON A PLANET IS ONLY MICROBES, IT WILL STILL PRODUCE OBSERVABLE SIGNATURES

• What might be the most easily detectable and unmistakable of these signatures?

• (A) Exotic atmospheric compositions (ozone, methane, etc.) that can only be formed by life

• (B) Phosphorescent light from bioluminescence

• (C) Changes in the planet’s atmosphere and surface

• (D) Good restaurants

Wednesday, August 13, 2014 SIGNATURES OF LIFE

• The best signifier of life is so-called biogenic gases, atmospheric gasses that can only be formed by life

• Some commonly suggested biogenic gasses are methane, ozone, nitric acid, and ammonia

• For a planet in another , this may be the only way to detect life that isn’t actively trying to communicate

Wednesday, August 13, 2014 DETECTING SIGNALS FROM EXTRATERRESTRIALS • Radio waves pass through the gas and dust in the without being absorbed, and are therefore probably the best way for one alien civilization to contact another

• Any signal would have to be very strong to be visible

• Many radio telescopes (including Arecibo, shown on the right) spend some time searching for messages from distant stars

Wednesday, August 13, 2014 OPINION POLL!

Wednesday, August 13, 2014 HAVE WE ALREADY BEEN CONTACTED BY ALIENS?

• (A) No

• (B) Yes, but we didn’t realize it

• (C) Yes, but the government is covering it up

• (D) Yes, but only in ancient times

Wednesday, August 13, 2014 THE WOW! SIGNAL

• A strong narrow-band radio signal detected by Jerry Ehman in 1977

• Observation lasted 72 seconds (due to telescope-the full signal may not have been observed), never detected again

• Matched the expected characteristics of an extraterrestrial signal fairly well

Wednesday, August 13, 2014 OPINION POLL!

Wednesday, August 13, 2014 IN YOUR OPINION, WHY HAVEN’T WE RECEIVED A DEFINITE SIGNAL FROM ALIENS?

• (A) They don’t exist

• (B) They do exist, but they don’t care, or are not trying

• (C) They do exist, but they cannot signal us (either they don’t have the technology yet, or have different )

• (D) They do exist and they know about us, but for some reason are unwilling to contact us

Wednesday, August 13, 2014 THE

• Physicist Enrico Fermi proposed that if extraterrestrial civilizations were common in the universe, they should be detectable in some way

• If so, then where are they? Why don’t we see them?

• Possible solutions are that intelligence is rare, or simply that life itself is rare, or that life is very difficult to detect

Wednesday, August 13, 2014 THE

• Developed by in 1961 as a way to think of the factors involved in the generation of civilizations

• Frequently used to calculate the number of civilizations in the galaxy, though this use is questionable

Wednesday, August 13, 2014 THE DRAKE EQUATION

N = R fp ne fl fi fc L ∗ × × × × × × • N is the number of civilizations in our galaxy we could communicate with right NOW

• R* is the rate of star formation per year in our galaxy (stars/year), (total # of stars/age)

• fp is the frequency of planets per star (planets/star)

• ne is the fraction of planets that are habitable (habitable planets/planet)

• fl is the fraction of these planets that do develop life (life/habitable planet)

• fi is the fraction of planets with life that develop intelligent life (intelligence/life)

• fc is the fraction of intelligent civilizations that releases detectable signals (communicating/int.)

• L is the length of time (in years) that a civilization releases detectable signals (years)

Wednesday, August 13, 2014 THE DRAKE EQUATION

N = R fp ne fl fi fc L ∗ × × × × × × ~7/year (100 Bn stars/13.6 Bn years)

~20% ~50% (1 in 5 stars has (recent studies indicate an earth-like that Sun-like stars may planet in the HZ) be closer to 100%)

Wednesday, August 13, 2014 THE DRAKE EQUATION N =7 0.5 0.2 f f f L × × × l × i × c × 1/3 to 1/1,000,000,000 (Earth//?)

very small to 1 100-10,000 years (fraction of all life? (Civilizations tend to last Or is it inevitable?) a few hundred years, but 1/25-1/3 how long will we last?) (, Neanderthals, Chimpanzees, Dolphins?, Pigs?, certain birds? (parrots, corvids?), whales?) Wednesday, August 13, 2014 THE DRAKE EQUATION

N = R fp ne fl fi fc L ∗ × × × × × × N =7 0.5 0.2 0.1 0.5 0.04 300 × × × × × × N =0.42 So my conclusion is that life in the galaxy is rare, and we are unlikely to ever contact another intelligent civilization (though, not incredibly unlikely-it is not unimaginable) However, if we take the upper estimates I provided, we get a much more generous number: N =7 0.5 0.2 0.3¯ 1 0.3¯ 10000 × × × × × × N 780 ≈ Wednesday, August 13, 2014 THE DRAKE EQUATION

N = R fp ne fl fi fc L ∗ × × × × × × N 780 ≈ • With this many civilizations currently existing, do we really have a chance to contact them?

• Assume uniform distribution throughout the galaxy:

• Volume = ~8x1012 cubic light years

• Volume per civilization ~ 1010 cubic light years

• Typical separation: ~1300 ly

Wednesday, August 13, 2014 THE DRAKE EQUATION

• Bottom line? The Drake equation can produce results from N = 10-20 to 36.4 million, meaning anything from “We are alone” to “The galaxy is crowded!”

• Is it a useful scientific tool to give us exact numbers of alien civilizations? Can we take people who use it this way seriously?

Wednesday, August 13, 2014 OUR EFFORTS TO CONTACT ALIEN CIVILIZATIONS

• SETI is not always passive, as with radio telescopes---we have made efforts to contact other civilizations

• The was a powerful radio signal emitted by the Arecibo radio telescope in Puerto Rico. Several similar signals followed

• The Pioneer and Voyager spacecraft all have plaques or, in the case of Voyager, a golden record, which attempts to carry vital information about the race to extraterrestrials

Wednesday, August 13, 2014 Wednesday, August 13, 2014 INTERSTELLAR TRAVEL

• Given current technologies, our understanding of physics, and capabilities, interstellar travel would take an impossibly long time

• The fastest human spacecraft (Voyager I) would take 80,000 years to reach the nearest star

• Various proposals for ‘generation ships’ (like mobile colonies) have been made, but the engineering task is too large as yet

Wednesday, August 13, 2014 DYSON SPHERES

• A theoretical structure built by a civilization with incredible engineering ability that completely surrounds a star and harnesses all of its energy

• Other forms, including a ring, or multiple rings have also been proposed

• Searches for these objects have found nothing

Wednesday, August 13, 2014 THE

• A metric for measuring a civilization’s technological advancement based on the amount of energy it uses

• First proposed in 1964 by

Wednesday, August 13, 2014 THE KARDASHEV SCALE

• Type I: Uses energy equivalent to the entire energy budget of a planet (total from solar radiation), ~1012

• Probably uses fusion , interplanetary spaceflight, etc.

• Type II: Harnesses the energy of an entire star, ~1026 Watts

• Interstellar colonization, , stellar engineering

• Type III: Harnesses the energy of an entire galaxy, ~1037 Watts

• Intergalactic travel, galactic-scale engineering

Wednesday, August 13, 2014 THE KARDASHEV SCALE

• Type 0: Uses some energy sources on a planet (mostly organic based sources, e.g. wood, oil, etc), easily destroyed by natural disasters/societal collapse

• Type IV: Harnesses the energy from all in the universe, effectively omnipotent

• Teleportation, matter/energy transformation, time travel

• Type V: Able to access the multiverse....

• Capable of engineering entire

Wednesday, August 13, 2014 THE KARDASHEV SCALE

• Humans today: 0.717 (Type 0--we don’t even make the scale)

• Type I: typical low sci-fi civilization (esp. in solar system), e.g. Neuromancer, KSR’s Mars series, Firefly, Ender’s Game

• Type II: Hi-tech sci-fi civilizations, e.g. Star Trek Federation, Ringworld builders, Covenant from Halo, Superman by himself

• Type III: Very hi-tech civilizations, e.g. Star Wars Empire

• Type IV/V: Seemingly all-powerful, e.g. Doctor Who Time Lords, Q Continuum from Star Trek, 2001 Monolith Builders, Contact

Wednesday, August 13, 2014 THE KARDASHEV SCALE

Wednesday, August 13, 2014 ACTIVITY TIME!

Wednesday, August 13, 2014 CLASS ACTIVITY

• Break into groups of 4-5

• Design and write down a message to send to extraterrestrials to let them know several important things about us:

• 1) Where we are

• 2) What we’re like

• 3) What we know (and that we’re intelligent)

• Think about how you would communicate this: aliens probably don’t speak English, and probably don’t look or think like us (do they even see, hear, and feel like us?)

Wednesday, August 13, 2014