1 / 44

Searching for ET

“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 Pimperne l. Searching for ET. A Scientific Recipe.

coyne
Download Presentation

Searching for ET

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. “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

  2. Searching for ET A Scientific Recipe

  3. Birth of SETISearch for Extra-Terrestrial Intelligence “… 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.” Searching for Interstellar Communications Nature vol. 184, no. 4690, pp 844-846 Sept. 19, 1959 GiuseppiCocconi and Philip Morrison

  4. Communication … the Basis • The 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. • Universal constants such as c (the speed of light), e (the unit of electrical charge), h (Planck’s constant) etc. characterize these laws. • Mathematics is the language in which these laws are expressed. • Communication cannot take place unless ET has discovered thoselaws and developed a mathematics in which to express them.

  5. Operational Intelligence • Radio waves—the optimum way to transmit information through space. Why? Fast—they travel at the speed of light. Radio photons are cheap…you can make 10 million of them for the same cost as 1 visible photon. They are penetrating, i.e., they easily travel through intergalactic dust and gas … and planetary atmospheres. In other words, ET must have reached the stage of “operational” intelligence, i.e., they must have discovered these laws and built a radio telescope.

  6. The Milky Way Galaxy ET Here? The distance to ET is on the order of 1000’s of light years!

  7. Space is Unimaginably Vast Milky Way can be approximated as a giant disk. Radius = 50000 LY Thickness = 2000 LY Volume = p(Radius)2 x Thickness V ~ 1.6 x 1013 LY3= 16 trillion cubic light years!

  8. How Far to Our Neighbors? If N = L/103 and L = 106 years, then there are 1000 civilizations in 16 trillion cubic LY… or 1 civilization in every 16 billion cubic LY Imagine every civilization surrounded by a bubble in which it is alone. V = 4/3 π R3 V ~ 16 billion cubic LY R ~ 1,600 LY Distance between civilizations: D = 2R ~ 3,200 LY! R R

  9. 2 – Way Communication? I’m here! Cool! 3200 LY Send message … Somewhere in the galaxy … far far away Receive response 6400 years later! In the inimitable words of Captain, Road Prison 36 (Strother Martin, Cool Hand Luke, 1967) …“What we got here … is failure to communicate.”

  10. Assume 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 species—we 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 years about 100 years about 1– 10 thousand years at least 1 million years a time longer than the age of the universe

  11. How Far to Our Neighbors? There are 1,000,000 civilizations in 16 trillion cubic LY, or … 1 civilization in every 16 million cubic LY Imagine every civilization surrounded by a bubble in which it is alone. V ~ 16 million cubic LY V = 4/3 π R3 R ~ 160 LY Distance between civilizations: D = 2R ~ 320 LY! • Assume Drake-Sagan are right and N = L … and, as we’ve assumed, L = 1,000,000 years … R R

  12. 2 – Way Communication? I’m here! Cool! 320 LY Send message … Somewhere in the galaxy … far far away Receive response 640 years later! In the inimitable words of Captain, Road Prison 36 (Strother Martin, Cool Hand Luke, 1967) …“What we got here … is still a failure to communicate.”

  13. Better 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. So…if, 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? For example, if N = L and L = 106yrs … if you pick an ET at random, what are the chances of picking one whose ‘age’ is < 50 yrs? It’s about 50/106 = 1/20,000! Yup … we’re the new kid on the block … better that we “listen” and try to “hear messages” from those “ancient” civilizations now broadcasting.

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

  15. water hole

  16. The “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 generate all radio transmissions eventually fall into this hole so that’s where all aliens should look all operationally intelligent civilizations would be aware of its significance and would think of sending and receiving signals within this spectral region radio telescopes cannot be tuned to frequencies outside this region —it is not a good choice! Intelligent civilizations would use lasers that produce visible light that can be targeted much better

  17. Where Look for ET and How? Where? Well, we’ve discussed this … essentially we should target F7—K2 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 doesn’t have to be so strong … but a much smaller number of targets can be examined at a given time!

  18. Wide Angle Field of View Target star Wide Angle FOV picks up radio waves from the entire region shown in the figure, but the circled star is G2V and that’s ET’s 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 noise…so

  19. Narrow Angle Field of View Narrow 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.

  20. Wide Angle FOV Target Narrow Angle FOV Target

  21. How Do We Carry Out a Search of Selected Targets? A very daunting task … • When do we “listen?” • (We can’t scan all the stars at once … so we might miss their transmission when we’re not looking.) • What frequency do we “set our dial to?” • (We don’t know what frequency the aliens use for their radio station.) • Where do we search for a signal? • (There are about 250 billion stars in the Milky Way Galaxy.) … but we’ll look at F7 ─ K2 and no binaries! • 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 … let’s take a look at an example of what we might expect.)

  22. When Do We Listen? • We want to look for ET’s 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’ …

  23. … Or our receiver is shutdown when ET is trying to ‘talk to us!

  24. What is ET’s “Channel?” We’ve guessed that ET is likely transmitting at a frequency somewhere in the “water hole” … somewhere between 1420 and 1720 Mhz but Suppose she’s not! Well … maybe we punt! Even if she is, there’s a 300 Mhz frequency band in the water hole! … (1420 ─ 1720 Mhz) How do we scan that band?

  25. Wide or Narrow Bandpass? • What is bandpass? Filter Amplitude Frequency Narrow Bandpass Wide Bandpass

  26. Wide bandpasspicks 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 bandpasspicks up only the desired frequency with minimal competing bacground noise … good! • ET’s 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!

  27. BETA ─ SETI BETA – SETI has been in operation since 1996. It receives 250 million channels simultaneously with a bandpassof 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.

  28. The ALFA Multibeam Receiver Scans 7 directions simultaneously at 1 Hz bandwidth frequencies ranging from 500 ─ 11000 Mhz!

  29. The Allen Telescopic Array ─ 350 Telescopes!

  30. The Arecibo Message • The 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”).

  31. 00000010101010000000000001010000010100000001001000100010001001011001010101010101010100100100000000000000000000000000000000000001100000000000000000001101000000000000000000011010000000000000000001010100000000000000000011111000000000000000000000000000000001100001110001100001100010000000000000110010000110100011000110000110101111101111101111101111100000000000000000000000000100000000000000000100000000000000000000000000001000000000000000001111110000000000000111110000000000000000000000011000011000011100011000100000001000000000100001101000011000111001101011111011111011111011111000000000000000000000000001000000110000000001000000000001100000000000000010000011000000000011111100000110000001111100000000001100000000000001000000001000000001000001000000110000000100000001100001100000010000000000110001000011000000000000000110011000000000000011000100001100000000011000011000000100000001000000100000000100000100000001100000000100010000000011000000001000100000000010000000100000100000001000000010000000100000000000011000000000110000000011000000000100011101011000000000001000000010000000000000010000011111000000000000100001011101001011011000000100111001001111111011100001110000011011100000000010100000111011001000000101000001111110010000001010000011000000100000110110000000000000000000000000000000000011100000100000000000000111010100010101010101001110000000001010101000000000000000010100000000000000111110000000000000000111111111000000000000111000000011100000000011000000000001100000001101000000000101100000110011000000011001100001000101000001010001000010001001000100100010000000010001010001000000000000100001000010000000000001000000000100000000000000100101000000000001111001111101001111000 … repeating … Why 1679?

  32. Decoding 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.

  33. How to Count in Binary… Decimal Binary

  34. The Arecibo Message Explained The boxes have been colored for clarity and “right to left parity” restored • Numbers 1-10 • Atomic numbers for H, C, N, O, P • Formulas for sugars, bases and phosphate in DNA nucleotides • Double helix structure of DNAwrapped around a binary number that represents the number of nucleotides in the human genome • Height of human being marked on the left and human population marked on right • Schematic of solar system (human stands on 3rd planet) • Arecibo transmitting telescope • Diameterof telescope

  35. The Numbers • The first bit pattern tells how humans count in binary from 1-10. • The Atoms of Life • 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.

  36. The DNA Molecule Sugar A T C5OH7 C5H4N5 C5H5N2O2 C5OH7 PO4 PO4 C G C5OH7 C4H4N3O C5H4N5O C5OH7 PO4 PO4 Phosphate

  37. The 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.

  38. Human 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 Drake’s height. Another 32-bit number, this one about four billion, is located on the right … gives the human population (back in 1974 --- it’s 7+ billion now). It tells aliens how large an army they need to conquer Earth.

  39. The 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.

  40. The 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.

  41. The Arecibo message consisted of 1679 bits since _______. • that's all the bits that could be sent before funding for the project ran out • 1679 is one more than 1678, the frequency of the radio wave that the water molecule emits • Sir Isaac Newton found a pulsar in M13 on Nov. 16, 1679 • The transmission frequency was set to 1679 Mhz • 1679 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

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

  43. Other Possible Methods of Communication Berkeley Lick Observatory 1m Berkeley 0.76 m Harvard 1.8m

  44. SETI@HOME • What 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 towww.setiathome.berkeley.edu

More Related