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The Search For Extraterrestrial Intelligence (SETI)
The Search For Extraterrestrial Intelligence (SETI)
The Search For Extraterrestrial Intelligence (SETI)
The Search For Extraterrestrial Intelligence (SETI)
The Search For Extraterrestrial Intelligence (SETI)
The Search For Extraterrestrial Intelligence (SETI)
The Search For Extraterrestrial Intelligence (SETI)
The Search For Extraterrestrial Intelligence (SETI)
The Drake Equation:
The Drake Equation:
Another way to see what the Drake equation represents:
Another way to see what the Drake equation represents:
Intelligence, technology
Intelligence, technology
Intelligence, technology
Intelligence, technology
Intelligence, technology
Intelligence, technology
Lifetime of the communicating phase
Lifetime of the communicating phase
TV leakage radiation
TV leakage radiation
TV leakage radiation
TV leakage radiation
Geographical distribution of TV stations
Geographical distribution of TV stations
Geographical distribution of TV stations
Geographical distribution of TV stations
What frequency should be used to listen or send interstellar messages
What frequency should be used to listen or send interstellar messages
Reasons for radio SETI:
Reasons for radio SETI:
Reasons for radio SETI:
Reasons for radio SETI:
The importance of bandwidth
The importance of bandwidth
The importance of bandwidth
The importance of bandwidth
The importance of bandwidth
The importance of bandwidth
SETI projects: partial historical list
SETI projects: partial historical list
SETI projects: partial historical list
SETI projects: partial historical list
Arecibo: message sent to M13 (1974): Globular cluster ~25,000 lyr away
Arecibo: message sent to M13 (1974): Globular cluster ~25,000 lyr away
Ohio State University SETI (1977-1997) With the Big Ear fixed
Ohio State University SETI (1977-1997) With the Big Ear fixed
Ohio State University SETI (1977-1997) With the Big Ear fixed
Ohio State University SETI (1977-1997) With the Big Ear fixed
Ohio State University SETI (1977-1997) With the Big Ear fixed
Ohio State University SETI (1977-1997) With the Big Ear fixed
SETI projects: partial historical list
SETI projects: partial historical list
SETI projects: partial historical list
SETI projects: partial historical list
SETI projects: partial historical list
SETI projects: partial historical list
SERENDIP
SERENDIP
SETI@home: Now searching for pulses
SETI@home: Now searching for pulses
SETI@home: Now searching for pulses
SETI@home: Now searching for pulses
SETI@home: Now searching for pulses
SETI@home: Now searching for pulses
SETI@home: Now searching for pulses
SETI@home: Now searching for pulses
SETI@home and distributed computing
SETI@home and distributed computing
Allen Telescope Array (ATA)
Allen Telescope Array (ATA)
The Search For Extraterrestrial Intelligence (SETI)

: John Scalo. , . , The Search For Extraterrestrial Intelligence (SETI).ppt zip- 7851 .

The Search For Extraterrestrial Intelligence (SETI)

The Search For Extraterrestrial Intelligence (SETI).ppt
1The Search For Extraterrestrial 17waterhole. Alien civilizations will know
Intelligence (SETI). AST 309 part 2: that these two lines are from the
Extraterrestrial Life. dissociation products of water, whatever
2The Drake Equation: N = N* fpl nhab fL they call H and OH. Not taken too
fC fT L/T. Stars? Planets? Habitable seriously, But convenient range to strive
Origin Complex Intelligence, Lifetime for. (Allen Telescope Array uses this
planets? of life? life? technology? of range, and more.). OTHER MAGIC
civilization. FREQUENCIES Some frequency based on
3Another way to see what the Drake combinations of fundamental constants of
equation represents: What is the nature? (e.g. speed of light, Plancks
likelihood or probability that the constant, ) The combination can be
sequence of events shown to the right will expressed without referring to our units
occur, ending up with the peculiar group (e.g. meters) Intergalactic frequency
of phenomena listed at the bottom standard based on temperature of cosmic
branching? And are there many other background radiation? Many others have
possible branchings that we havent been suggested. Too many! None in use
thought of, or are incapable (for, say, today.
biological reasons) of imagining? 18SETI projects: partial historical
4Intelligence, technology. list. Ozma (1960) In 1960, radioastronomer
IntelligenceIf we want to communicate Frank D. Drake, then at the National Radio
with aliens, they must have something like Astronomy Observatory (NRAO) in Green
what we usually call intelligence. What Bank, West Virginia, carried out
does this mean? Are there different humanity's first attempt to detect
types? What about other animals? Other interstellar radio transmissions. The
cultures? Especially oral tradition stars chosen by Drake for the first SETI
cultures. Why did humans evolve such big search were Tau Ceti and Epsilon Eridani.
brains? Why think that extraterrestrials From April to July 1960, for six hours a
would share our forms of cognition? Factor day, Project Ozma's 85-foot NRAO radio
in Drake equation: What is probability telescope was tuned to the 21-centimeter
that life elsewhere develops emission (1420 MHz) coming from cold
intelligence? Call it fI . hydrogen gas in interstellar space. A
Communication, technologyIf we want single 100 Hz channel receiver scanned 400
signals, the aliens must have some kind of kHz of bandwidth. The astronomers scanned
system of representation, like a language. the tapes for a repeated series of
How likely? Other forms? Musical? uniformly patterned pulses that would
Unimaginable? And no matter what kind of indicate an intelligent message or a
language they have, they have to be series of prime numbers such as 1, 2, 3, 5
technological civilizations if they are to or 7. With the exception of an early false
send signals across the Galaxy. We could alarm caused by a secret military
enter these topics as two more experiment, the only sound that came from
probabilities, fC fT . N(planets with life the loudspeaker was static and no
that also developed intelligence and meaningful bumps superimposed themselves
technology) = N* fpl nhab fL fC fT. on the formless wiggles on the recording
5Lifetime of the communicating phase. paper.
We left out one crucial factor: The 19Arecibo: message sent to M13 (1974):
fraction of the Galaxys age T that a Globular cluster ~25,000 lyr away Message
civilization is in the technologically written by Drake, Sagan, et al. Frequency:
communicating phase. We know the age of 2380 MHz 1679 binary digits. SETI
our Galaxy is T ~ 10 billion years. projects: partial historical list.
Consider our chances if civilizations only 20Ohio State University SETI (1977-1997)
last for 100 years Average length of time With the Big Ear fixed radiotelescope
spent in the communicating phase L. (used Earths rotation to scan the sky)
Sometimes referred to as lifetime of a August 15, 1977: detected a strong
technological civilization. Call it L. Our narrow-band signal for 72 secs: SETI
final Drake equation is then: N = N* fpl projects: partial historical list.
nhab fL fC fT (L/age of Galaxy) This Duration consistent with extraterrestrial
represents the number of communicating source Strength: 30 times above background
civilizations in our Galaxy. We have been noise Frequency: 1420 MHz (neutral H)
this way for only ~ 100 yr. If this were Bandwidth: <10 kHz.
L, then N (number of civilizations for 21SETI projects: partial historical
communication in our Galaxy) would be list. The location of the signal in the
around 1. Even if N ~ 100, there is no constellation Sagittarius, near the Chi
hope for two way communication, and Sagittarii star group. RA= 19h25m31s 10s
probably very difficult to locate them or 19h28m22s 10s declination= ?2657?
among a 100 billion possibilities. And too 20? There were ~50 follow-up searches
far for biosignatures. In order for our performed in this area, but nada =>
Drake equation N to come out reasonably Origin of the Wow! signal is still
large (say a million), the average undetermined.
lifetime L must be extremely large, 22SETI projects: partial historical
something like 100,000 to a million years. list. NASA asks for SETI proposal,
? This means we can expect any nearby astronomers propose Project Cyclops,
civilizations to have had a long lifetime, 1000 100 meter radio telescopes on back
i.e. be very advanced. I think this is the side of moon, costing $10 billion (1970s).
only thing we can know with any certainty NASA asks for more moderate plan, planning
about extraterrestrial civilizations: If for next ~ 17 years. Ohio State SETI:
there are enough of them to make it likely 1977-1997 (replaced by golf course). Best
we will find them, then they must be very known for the wow signal. Harvard, Paul
advanced (using beacons)! Horowitz and Project META (millions of
6SETI web sites. SETI at Space.com bands in frequency), Project BETA (billion
http://www.space.com/searchforlife/index.h bands in frequency). Horowitz and Sagan
ml SpaceRef.com 1993 Astrophysical Journal summarize
http://www.spaceref.com/Directory/Astrobio results. One of first SETI papers in
ogy_and_Life_Science/seti/ Ongoing SETI refereed journal. Harvard and Horowitz now
searches: SETI Institute/Allen Telescope converted to Optical SETI, largest in
Array http://www.seti.org/ Project world. UC Berkeleys Project SERENDIP.
SERENDIP, UC Berkeley Since 1977! Part of data analyzed by 5
http://seti.ssl.berkeley.edu/serendip/sere million home computers through SETI@home.
dip.html SETI@home Dec. 1991. NASA funds $100 million SETI
http://setiathome.berkeley.edu/ Sourthern effort (MOP). Detailed plan for combined
SERENDIP, Univ. Western Syndey targeted and sky survey searches. 1993:
http://seti.uws.edu.au/ SETI Italia Funding removed by senate amendment
http://www.seti-italia.cnr.it/ Optical Project Phoenix (SETI Institute) rises
SETI at Berkeley from the ashes. Piggy-backs off various
http://seti.ssl.berkeley.edu/opticalseti/ radio telescopes, mainly Arecibo. 2001:
Harvard http://seti.harvard.edu/oseti/ Paul Allan and others fund the Allen
Amateur SETI: Project BAMBI Telescope Array, 350 6meter telescopes. 42
http://www.bambi.net/ SETI League complete by Oct. 2007.
http://www.setileague.org/ Project ARGUS 23SERENDIP. One of oldest operational
http://www.setileague.org/argus/index.html SETI searches--since 1979, UC Berkeley.
7STRATEGIES FOR COMMUNICATION WITH 1997--installed as piggyback at Arecibo
EXTRATERRESTRIAL CIVILIZATIONS. ?SETI is radio observatory (picture below), largest
concerned with searches for signals from single-dish radio telescope in world (but
extraterrestrial civilizations, not can only point in one direction). SERENDIP
spectral biomarkers we discussed earlier = Search for Extraterrestrial Radio
in course, or actual travel to other star Emissions from Nearby Developed
systems. ? Except for 1974 signal to Intelligence Populations. SERENDIP IV is
globular cluster M13 (thousands of light the fourth instrument of the project,
years away), we only try for reception, no collects data by 'piggybacking' on top of
transmission. (What if they are all the Arecibo radio telescope. SERENDIP IV
listening?) ? Signals could be instrument is basically a 200 billion
intentional (they are trying for contact) operations per second supercomputer that
or nonintentional (we eavesdrop, one way scans 168 million narrow (0.6 Hz) channels
or another). A few unintentional every 1.7 seconds for signals that are
candidates listed on next slides, but we significantly 'louder' than the background
are most concerned with intentional static. Some of its data is analyzed
signals, and with establishing a two-way through SETI@home for desktop
conversation. ? Remember: Distance to even computers--so far millions of users,
the nearest 1000 or so stars ~ 50 light largest distributed computing project in
years, and we expect only a tiny fraction world, led to ~ 100 other distributed
of them to have life, let alone computing projects, e.g. folding@home,
intelligent communicating life, so we are prime@home, climatenet@home, (details on
necessarily asking whether to undertake a next slide). The Arecibo radio telescope
search with a guaranteed very low in Puerto Rico, used by both SETI Insitute
probability of success, and, even if for Project Phoenix, and by UC Berkeley
successful, communications will involve for their SERENDIP IV.
decades or even centuries. You can see why 24SETI@home: Now searching for pulses.
funding for SETI is sparse! August 2008: SETI@home switches to search
8Four types of nonintentional types of for pulsed radio signals. Observations are
signals: Leakage radiation from radio, TV, from SERENDIP piggy-backed on radio
or other radio broadcasts. Earth as telescope at Arecibo that is built into a
example: Many TV stations broadcasting mountain. This dish only points in one
different shows, or same shows at direction as sky drifts across this
different times, radio waves emanating direction--the drift takes about 12
from Earth have always been incoherent, seconds for a given point in the sky.
completely scrambled. It is not true that SETI@home searches for signals that rise
alien ETI could be seeing our early TV and fall in 12 seconds--any object will do
shows! Alien communications, e.g. between this, but most will be broad-band sources
home planet and colonies. We would have to (top image). Narrow search by requiring
be almost exactly in the line of sight narrowband signal (2nd image). Will check
between home planet and colony, and guess for several different bandwidths.
the frequency range. Seems very unlikely. Information in image? Search for pulsed
Dyson spheres -- hypothetical constructs signal (3rd image). If from planetary
built by advanced civilizations in order system, should also be Doppler shifting
to collect nearly all the energy of their (chirped signal), as in 4th image. Home
parent star. Spherical shell at same computers look for various combinations of
distance from star as the home planet. The frequencies, bandwidths, and chirp rates.
intercepted energy is somehow channeled to See if you can understand why the white
planet. But shell is heated by the thing in the illustration below might be
incident radiation: What will its a signal SETI@home screensaver Can you
temperature be? At what wavelength would see the alien signal??
you conduct a search for Dyson spheres? 25SETI@home and distributed computing.
Products of technological activity e.g. By 2007 over 40 projects had joined the
gamma rays from their (hypothetical) BOING distributed computing family, using
fusion propulsion systems, CFC molecules the software provided by SETI@home.
from their air conditioners Protein folding: folding@home,
9TV leakage radiation. World TV predictor@home, Rosetta@home,
spectrum. World TV power vs. time. Proteins@home Primegrid.com: privately run
10Geographical distribution of TV mathematical project that searches for
stations. Geographical distribution of TV very large prime numbers and has already
stations. As Earth rotates, this pattern found more than 100 new primes.
of populated areas is the only evidence Einstein@home is based at the University
for TV broadcasts. of Wisconsin in Milwaukee and searches for
11How would an alien civilization try to pulsars in the sky based on data from the
communicate across many light years of gravitational wave detectors LIGO and GEO.
space? The only thing that is almost climateprediction.net: Oxford Univ. UK
certain is that they will use high-profile climate simulator. Jan 2005:
photonsfastest and cheapest way to First paper in Nature, 2,570 simulations
transmit information that exists (as far of Earth. By 2007: 50,000 simulations.
as we know). Even though photon signals Goal is several million, to explore 23
are the only choice we can think of, that parameters of the climate model.
still leaves many considerations that we 26Allen Telescope Array (ATA).
need to guess about: Where to point our Eventually 350 6 meter antennas,
telescopes? What kind of stars should we equivalent to 100 meter single dish. 42
point our telescopes toward? Or would it dishes saw first light in Oct 2007.
be better to survey the whole sky? Entered hibernation due to funding
Wavelength: What wavelength region should problems this year! => Maybe restart in
we expect is optimum for sending Sep 2011 due to private donations >
interstellar signals? Radio? Optical? $200,000 Unique features: ? Large field of
Other? Bandwidth: What range of view, so can scan sky faster in survey
wavelengths? Broadband or narrow-band? mode. ? Large range of frequencies (1-10
WHY? Recognition and Interpretation: How GHz for targeted search, five times range
would a message, or some sign that it is of Phoenix), and small bandwidth (~ 1Hz),
not a natural phenomenon, be using more than a billion channels. ?
distinguished, and how would a meaningful Finally offers SETI 24/7 monitoring
message be encoded? Well discuss each of (Phoenix had Arecibo for only about 3
these in turn. weeks per year 1998-2004) Goals: ?
12WHERE TO POINT? a. Sky survey. Survey Targeted search: Survey 106 stars with
entire sky with telescopes beam this good sensitivity between 1 and 10 GHz for
might involve millions of directions for weak non-natural transmitters. ? Sky
typical radio telescopes. If you want to Survey ~ monitors inner Galactic plane in
finish in your lifetime, you could only water hole range 1420-1720 MHz for very
spend a very brief time on each direction, strong non-natural transmitters.
so you could only detect very strong 27Optical SETI (OSETI). When faced with
signals. But at least you wont miss any the question What kind of signals would
of them. And the method doesnt make any alien civilizations transmit, the
assumptions about what the most likely traditional answer has been: Continuous
stars are for signal reception. ? This is narrow-band radio transmissions An
a low-sensitivity method, but complete for alternative: Maybe they would send
strong signals. b. Targeted search. Point distinct broad-band pulses. They would
at the nearest (less than about 50 to 1000 stand out against background noise not
l.y.) stars roughly like the sun and because they are precisely centered on a
cooler (recall conditions for habitable particular wavelength, but because they
planets). Could detect weaker signals, are very short and punctuated bursts of
i.e. would have higher sensitivity. But energyunlike most other natural
you will only cover a tiny fraction of the phenomena. This is the world of Optical
sky. ? This is a high-sensitivity method, SETI, which searches for signal in the
but severely incomplete. Most current visible (or infrared in future) light
searches have shifted to a sky survey mode range, usually looking for nanosecond
(a) However plans change rapidlythe Allen pulsed laser radiation. Reasons: Radio
Telescope Array (largest current project) 21cm line has huge noise problem with
combines both approaches. And some interstellar gas. Laser-like signals are
optical SETI searches (see below) are tightly beamed, so can be sent over very
targeted searches. large distances (no loss due to
13What frequency should be used to inverse-square law). With current
listen or send interstellar messages? From equipment can send out pulsed laser beam
the Earths surface, most radiation is 5000 times brighter than the Sun
blocked by the atmosphere. The exceptions Unidirectional--can pinpoint direction
are optical (visual) and radio photons. with high precision. Higher frequency
Earths atmosphere also blocks out most of --can encode more information. There are
the infrared part of the spectrum due to two OSETI programs at UC Berkeley, and now
water vapor in our atmosphere. From the ongoing or about-to-launch OSETI searches
highest mountains or a jet plane, the at Harvard, Lick Observatory, and Columbus
infrared is barely accessible, but not for Observatory. Current projects: Berkeley:
the continuous kinds of surveys we have in Monitors 2500 stars as part of exoplanet
mind. Note that if we could do such a search. Searches for ultra-narrow band
survey from Earth orbit (expensive), or, signals. Harvard: since 1998, using 61
if we only had about $100 billion dollars inch telescope. Nearly 100,000
so that we could build a facility for SETI observations. Dec. 2000: new 72 inch
on the far side of the moon (Project telescope dedicated to an all-sky survey.
Cyclops), our considerations might be Can detect nanosecond (billionth of a
different. Why have most SETI searches second) pulses and cover entire sky in 200
concentrated on radio wavelengths instead nights. Lick Observatory Targeted search
of optical? A single amazingly influential began in 2000. First results published in
paper by Cocconi and Morrison (1960 Stone et al. 2005 Astrobiology. 14
Nature) set the stage. Their arguments for candidate events.
radio SETI are on next slide. 28Encoding a message. ?SETI researchers
14Reasons for radio SETI: 1. focus on a signal anyone could comprehend.
Interstellar dust selectively blocks Not clear this is sensible! ? It is very
shorter wavelengths (higher frequencies) sensible to expect digital, binary, not
strongly suggests we use the IR or radio analogue signal. ? How to encode a picture
parts of the spectrum (long wavelengths or into a string of binary (0,1) signals? The
small frequencies). But IR is dominated by simplest and most efficient way to encode
Earths atmospheric molecular emission if a message (we think) is binary code. Use
search from surface, so that leaves radio. only 2 characters, e.g. a 1 and a 0, or a
Notice that radio SETI allows reception + and a - , or "on" and
from the entire galaxy, but optical isnt "off", ... Each 1 or 0 (or
that bad, since we can see stars out to ~ whatever) is a "bit". Then the
1 kpc. Besides, most radio searches are message can just be sent as a series of
concentrating on nearby stars anyway. (We pulses. Expect the message to be a
dont want 1000-year conversations.) 2. two-dimensional picture that is encoded in
Radio photons are cheaper to send than a one-dimensional binary string that
optical photons (because energies are ~ factors into prime numbers. e.g. 551 = 29
100,000 times smaller for radio). 3. The x 19 (or 19 x 29); 1679 = 23 x 73 (the
main consideration is noise: Here noise 1974 Arecibo transmission). Example: We
means anything that is not an alien receive signal 1111100000101011010110101.
signal--any kind of interference. We This factors into 5 x 5, giving a picture
should listen (or send) where the noise is of the greek letter "pi". Or try
minimized, so that we can recognize the the letter "E", etc. But why
(probably weak) signal. Noise is minimum would ETI send out signals that anyone
in a region of the radio part of the could decode? Perhaps they send out
spectrum. This is summarized in a classic signals which could be understood only by
graph shown on next slide. Arecibo Home of others who are already "at the same
SERENDIP, SETI@home, Phoenix. Allen level" as they are. What would be a
Telescope Array, SETI Institute, N. Calif. difficult signal for us to recognize?
15Alien signaling: Choosing a wavelength Maybe the test would be to recognize some
range that minimizes noise -- anything sort of "meaning" in the
that is not an alien signal. Avoid very message. (Think about musical signals. At
low frequencies (wavelengths too large), present, there is no viable theory of
because synchrotron radiation from musical meaning in music analysis,
supernova remnants dominates there. (Far philosophy, cognitive science, pattern
left in figure) Avoid frequencies higher recognition, or any other field that has
than about 10 GHz because of H2O and O2 approached the problem.) Deeper questions:
emission from Earths atmosphere. Cosmic Will symbolic communication systems be
microwave background radiation sets universal among intelligent creatures? Is
floor at intermediate frequencies, and grammaticity hard-wired into our brains?
that is where the noise is minimum, and Another example of single mutation?
where we should search. A message will 29The Eerie Silence.. ? SETI has been
arrive in a narrow wavelength band or on-going for about 50 years and NOTHING
bands, not spread over the whole 1-10 GHz has been detected ? Conclusion: are we
region. There are 10 billion 1 Hz bands in alone? Are there no ETIs in our galaxy? ?
this range. How to decide which ones to No, not yet. But they are probably no
pick? First, must understand bandwidth. nearby ETIs similar to us, nor a nearby
16The importance of bandwidth. Basic strong radio beacon intended to notify us
idea: Can pack more power in a narrow of ETIs presence. There are many stars
frequency range (narrowband signal) than not observed yet, so many frequencies not
spreading out over a large range explored and many other possible ways for
(broadband signal). So can distinguish a ETIs to communicate.
narrowband signal from the background more 30What IF The Eerie Silence is broken!
easily. Think of the everyday radio What then? There is actually a so-called
analogy again, and it should be clear! SETI Post Detection Task Group (a
SETI@home: Each vertical band is a 10 permanent study group of the International
kHz slice of the 2.5 MHz wide SERENDIP Academy of Astronautics). Its only a
data. There are 250 such slices. But think tank, no legal status, no
search is for signals much narrower than governmental involvement. In case a signal
these bands. is detected the task group would advise to
17Which frequency? If it is true that perform the following steps: Verify
narrow-band signal is the only sensible authenticity of ETI signal Contact the
approach, how will we decide which band to International Astronomical Union =>
use? Suggested beacon frequencies (or which will contact UN. inform the
hailing frequencies or magic government of the country (countries)
frequencies): HI (neutral hydrogen) 21cm where radio telescope is located Public
(wavelength) line? The frequency is 1420 announcement Such a discovery will have
Megahertz = 1.42GHz Natural, abundant, but unprecedented and enormous scientific,
lots of interference by interstellar gas. social, cultural, political and spiritual
(Latter has apparently been forgotten.) OH consequences for humanity. Nobody knows
line at 1.7 GHz? H + OH = H2O, so maybe what will happen (depends on nature of
region between these two --> the signal, e.g. distance to source).
The Search For Extraterrestrial Intelligence (SETI).ppt
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The Search For Extraterrestrial Intelligence (SETI)

The Search For Extraterrestrial Intelligence (SETI)

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