Contacting Aliens

We seek him here, we seek him there,Those Frenchies seek him everywhere.Is he in heaven?Is he in hell?That dammed, elusive Pimpernel.Sir Percy Blakeney, Chapter 12, The Scarlet Pimpernel

Searching for ETA Scientific Recipe2Birth of SETISearch for Extra-Terrestrial IntelligenceSearching for Interstellar CommunicationsNature vol. 184, no. 4690, pp 844-846Sept. 19, 1959Giuseppi Cocconi and Philip Morrison The reader may seek to consign these speculations wholly to the domain of science-fiction. We submit, rather, that the foregoing line of argument demonstrates that the presence of interstellar signals is entirely consistent with all we now know, and that if signals are present, the means of detecting them is now at hand.Few will deny the profound importance, practical and philosophical, which the detection of interstellar communications would have. We, therefore, feel that a discriminating search for intelligent signals deserves a considerable effort. The probability of success is difficult to estimate; but if we never search, the chance of success is zero.3Communication the BasisThe building blocks of nature and the fundamental laws of physics that describe their behavior are universal, i.e., they are the same for ET as they are for us.Mathematics is the language in which these laws are expressed.Communication cannot take place unless ET has discovered those laws and developed a mathematics in which to express them.Universal constants such as c (the speed of light), e (the unit of electrical charge), h (Plancks constant) etc. characterize these laws.4Operational IntelligenceIn other words, ET must have reached the stage of operational intelligence, i.e., they must have discovered these laws and built a radio telescope.

Radio wavesthe optimum way to transmit information through space.Why?Radio photons are cheapyou can make 10 million of them for the same cost as 1 visible photon.Fastthey travel at the speed of light.They are penetrating, i.e., they easily travel through intergalactic dust and gas and planetary atmospheres.5The Milky Way Galaxy

ET Here?The distance to ET is on the order of 1000s of light years!6Space is Unimaginably VastMilky Way can be approximated as a giant disk.Radius = 50000 LYThickness = 2000 LY

Volume = p(Radius)2 x ThicknessV ~ 1.6 x 1013 LY3 = 16 trillion cubic light years!217How Far to Our Neighbors?If N = L/103 and L = 106 years, then there are 1000 civilizations in 16 trillion cubic LY or1 civilization in every 16 billion cubic LYImagine every civilization surrounded by a bubble in which it is alone.

V = 4/3 R3V ~ 16 billion cubic LYR ~ 1,600 LYDistance between civilizations:D = 2R ~ 3,200 LY!RR218

2 Way Communication?

Im here!Cool!Send message Receive response 6400 years later!Somewhere in the galaxy far far awayIn the inimitable words of Captain, Road Prison 36 (Strother Martin, Cool Hand Luke, 1967) What we got here is failure to communicate.3200 LY9Assume that all the multiplicative factors in the Drake equation lead us to the conclusion that N = L/10 3, where L is in years. Then if the lifetime of the human species is typical of the lifetime of other specieswe estimate that L = 1 million years and therefore N=1000. Given this, roughly how long would it take to exchange a single message with one of those civilizations?about 10 yearsabout 100 yearsabout 1 10 thousand yearsat least 1 million yearsa time longer than the age of the universe

21How Far to Our Neighbors?There are 1,000,000 civilizations in 16 trillion cubic LY, or 1 civilization in every 16 million cubic LYImagine every civilization surrounded by a bubble in which it is alone.

V ~ 16 million cubic LYV = 4/3 R3R ~ 160 LYDistance between civilizations:D = 2R ~ 320 LY!RRAssume Drake-Sagan are right and N = L and, as weve assumed, L = 1,000,000 years 2111

2 Way Communication?

Im here!Cool!Send message Receive response 640 years later!Somewhere in the galaxy far far awayIn the inimitable words of Captain, Road Prison 36 (Strother Martin, Cool Hand Luke, 1967) What we got here is still a failure to communicate.320 LY12Better to Receive Rather Than Give

If there are lots of alien civilizations how many of them are older than ours?Our galaxy is about 10 billion years old.Life emerged on Earth at least 3.5 billion years ago.We became operationally intelligent only 50 years ago.Soif, blindfolded, you pick at random one kid out of all the kids in SLC, grades K 12+, what would be the odds of picking a kindergartner who just learned to read?Its about 50/106 = 1/20,000! Yup were the new kid on the block better that we listen and try to hear messages from those ancient civilizations now broadcasting.For example, if N = L and L = 106 yrs if you pick an ET at random, what are the chances of picking one whose age is < 50 yrs?13

1420 mhz1720 mhz somewhere between 1420 and 1720 mhz on your radio dial.The Optimum Frequency to Tune In?The Water Hole

water holeThe water hole radio frequency region between 1420 MHz generated by neutral hydrogen atoms and 1720 MHz generated by hydroxyl (OH) radicals is a good choice for interstellar communications because _____.they are the easiest frequencies to generateall radio transmissions eventually fall into this hole so thats where all aliens should lookall operationally intelligent civilizations would be aware of its significance and would think of sending and receiving signals within this spectral regionradio telescopes cannot be tuned to frequencies outside this regionit is not a good choice! Intelligent civilizations would use lasers that produce visible light that can be targeted much better

Where Look for ET and How?Where?Well, weve discussed this essentially we should target F7K2 stars.How?A Telescope with a wide angle field of view targets lots of stars at once but picks up a lot of unwanted radio noise so signal has to be very strong!A Telescope with a narrow field of view targets a particular star but this strategy eliminates background radio noise so signal doesnt have to be so strong but a much smaller number of targets can be examined at a given time!17

Wide Angle Field of ViewWide Angle FOV picks up radio waves from the entire region shown in the figure, but the circled star is G2V and thats ETs home star! Obviously, if ET is far away, his signal will be weak when it arrives at Earth. If it is to be detectable it must stand out above background noisesoTarget star21

Narrow Angle Field of ViewNarrow angle FOV picks up radio waves only from small region therefore less interference from region surrounding the target and a weaker signal can be detected.21Narrow Angle FOV TargetWide Angle FOV Target21How Do We Carry Out a Search of Selected Targets?Where do we search for a signal?(There are about 250 billion stars in the Milky Way Galaxy.) but well look at F7 K2 and no binaries!When do we listen?(We cant scan all the stars at once so we might miss their transmission when were not looking.)What frequency do we set our dial to?(We dont know what frequency the aliens use for their radio station.)What bandpass do we use?(We can easily pick up a lot of frequencies at once with a wide bandpass but we also pick up a lot of noise. We can eliminate much of the noise by using a narrow bandpass, but then we only pick up one particular frequency.)What language will the aliens use?(Well lets take a look at an example of what we might expect.)A very daunting task 21When Do We Listen?We want to look for ETs as far from us as possible. That implies that we adopt a narrow angle field of view targeting strategy but We could be scanning a solar system where ET resides but suppose his transmitter is shut down for maintenance 22

Or our receiver is shutdown when ET is trying to talk to us!21What is ETs Channel?Weve guessed that ET is likely transmitting at a frequency somewhere in the water hole somewhere between 1420 and 1720 Mhz butSuppose shes not!Well maybe we punt!Even if she is, theres a 300 Mhz frequency band in the water hole! (1420 1720 Mhz)How do we scan that band?2124Wide or Narrow Bandpass?What is bandpass?

AmplitudeFrequencyFilterNarrow BandpassWide Bandpass25Wide bandpass picks up a lot of frequencies at once good!But it also picks up a lot of background noise this means signal has to be strong to be detectable bad!Narrow bandpass picks up only the desired frequency with minimal competing bacground noise good!ETs signal will be about 0.1 0.5 Hz wide because of an effect called interstellar broadening. But, there are roughly 600 million 0.5 Hz wide channels within the 300 Mhz region of the water hole so you need a receiver capable of picking up 600 million channels at the same time when you scan a target bad!BETA SETI has been in operation since 1996. It receives 250 million channels simultaneously with a bandpass of 0.5 hertz per channel. It scans through the water hole from 1400 to 1720 Megahertz in eight hops, with two seconds of observation per hop. BETA automatically re-observes candidate signals by observing the sky simultaneously at two different directions with two separate BETA receivers, one scanning slightly to the east and the other slightly to the west. A successful candidate signal would first transit the east FOV and then the west FOV with a speed determined by Earth's rotation rate. A third BETA receiver observed the horizon to veto out signals of obvious terrestrial origin.BETA SETI

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The ALFA Multibeam ReceiverScans 7 directions simultaneously at 1 Hz bandwidth frequencies ranging from 500 11000 Mhz!21

The Allen Telescopic Array 350 Telescopes!The Arecibo MessageThe opportunity arose in 1974 to send a message from the giant Arecibo radio telescope Drake sent it towards the globular cluster, M13. It consisted of a repeating string of 1679 binary bits (0 or 1).

3000000010101010000000000001010000010100000001001000100010001001011001010101010101010100100100000000000000000000000000000000000001100000000000000000001101000000000000000000011010000000000000000001010100000000000000000011111000000000000000000000000000000001100001110001100001100010000000000000110010000110100011000110000110101111101111101111101111100000000000000000000000000100000000000000000100000000000000000000000000001000000000000000001111110000000000000111110000000000000000000000011000011000011100011000100000001000000000100001101000011000111001101011111011111011111011111000000000000000000000000001000000110000000001000000000001100000000000000010000011000000000011111100000110000001111100000000001100000000000001000000001000000001000001000000110000000100000001100001100000010000000000110001000011000000000000000110011000000000000011000100001100000000011000011000000100000001000000100000000100000100000001100000000100010000000011000000001000100000000010000000100000100000001000000010000000100000000000011000000000110000000011000000000100011101011000000000001000000010000000000000010000011111000000000000100001011101001011011000000100111001001111111011100001110000011011100000000010100000111011001000000101000001111110010000001010000011000000100000110110000000000000000000000000000000000011100000100000000000000111010100010101010101001110000000001010101000000000000000010100000000000000111110000000000000000111111111000000000000111000000011100000000011000000000001100000001101000000000101100000110011000000011001100001000101000001010001000010001001000100100010000000010001010001000000000000100001000010000000000001000000000100000000000000100101000000000001111001111101001111000 repeating Why 1679?31Decoding the Message

Arrange the 1679 bits into a matrix of boxes of 23 columns of 73 rows (23 and 73 are the two prime numbers when multiplied together equal 1679).Color the box with a 1 black and a box with a 0 white . The image is parity reversed, i.e., it was generated by scanning right to left, i.e., the first bit in the message occupies the upper row, rightmost cell. The next bit is the in the top row, next cell proceeding to the left. could be that aliens are left-handed? but the "handedness" of the image is completely irrelevant.32How to Count in Binary10110110000010203040506070809108421 Decimal23222120Number00000000110010200113010040101501106011171000810018101010DecimalBinary33The Arecibo Message ExplainedNumbers 1-10

Atomic numbers for H, C, N, O, P

Formulas for sugars, bases and phosphate in DNA nucleotides

Double helix structure of DNA wrapped around a binary number that represents the number of nucleotides in the human genomeHeight of human being marked on the left and human population marked on rightSchematic of solar system (human stands on 3rd planet)

Arecibo transmitting telescope

Diameter of telescope

The boxes have been colored for clarity and right to left parity restored34The NumbersThe first bit pattern tells how humans count in binary from 1-10.

The numbers provide the key for interpreting the next bit pattern a list of the atomic numbers of the five elements that make up DNA.

The Atoms of LifeAtomicNumber Element 1 Hydrogen 6 Carbon 7 Nitrogen 8 Oxygen 15 Phosphorus 35The DNA Molecule

C5OH7C5OH7C5OH7C5OH7PO4PO4PO4PO4C5H4N5C5H5N2O2C4H4N3OC5H4N5OATCGSugarPhosphate36The Structure of DNA and Size of the Human Genome

The structure of DNA is a double helix. If the aliens synthesize the molecule using the previously decoded components, they would see that DNA did form a double helix, which would confirm that they had decoded its chemical makeup correctly.A 32-bit number sits in the middle of the double helix that gives the approximate number of nucleotides in the human genome, about six billion.37Human Shape, Size, and Population

This bit pattern depicts a human at least it does to another human. What an alien would make of it is less obvious.To the left of the the human are the binary digits 0111 (14) in the middle of a dimension bar that denotes the height of the human the human is 14 tall 14 what? The only possible scale is based on the universality of the speed of light c. In SI units, it is c=3x108 m/s. The signal was broadcast at the frequency f = 2380 Mhz. The recipient knows the wavelength of the received message is: L = c / f = 12.6 centimeters in our units (--- some other number of alien units). This provides a length scale for the alien. 14 of these units is 176 cm, which is Frank Drakes height.Another 32-bit number, this one about four billion, is located on the right gives the human population (back in 1974 --- its 7+ billion now). It tells aliens how large an army they need to conquer Earth.38The Solar System

This schematic represents the Sun and planets of the solar system. The gas giants are all larger than the terrestrial planets, with Jupiter and Saturn indicated as larger than Uranus and Neptune to their right. Earth appears directly below the figure of the human and is offset in that direction, identifying it as the planet where humans live --- third rock from the Sun.39The Arecibo Telescope

The pattern represents the Arecibo radio telescope used to transmit the message, with dimension bars and a number binary 100101111110 at the bottom giving its diameter decimal 2430 the number of units of the 12.6 centimeter wavelength scale. Thus, the size of the antenna is 30,618 centimeters, or 306 meters.40The Arecibo message consisted of 1679 bits since _______.that's all the bits that could be sent before funding for the project ran out1679 is one more than 1678, the frequency of the radio wave that the water molecule emitsSir Isaac Newton found a pulsar in M13 on Nov. 16, 1679The transmission frequency was set to 1679 Mhz1679 is the product of two prime numbers, 23 and 73 and if the bits were arranged in 23 columns and 73 rows, a message appeared in picture form

Other Possible Methods of CommunicationHigh intensity, short (1 nsec) laser light pulses.Other Possible Methods of Communication

Berkeley Lick Observatory 1mHarvard 1.8mBerkeley 0.76 m

SETI@HOMEWhat is SETI@home?SETI@home is a scientific experiment that uses Internet-connected computers in the Search for Extraterrestrial Intelligence (SETI). You can participate by running a free program that downloads and analyzes radio telescope data.Go to www.setiathome.berkeley.edu2144Searchin'The CoastersYakety Yak & Other HitsiTunes v6.0.1.3, QuickTime 7.0.3