NSCI 314LIFE IN THE COSMOS16 - INTERSTELLAR COMMUNICATION IIDr. Karen KolehmainenDepartment of Physics, CSUSBhttp://physics.csusb.edu/~karen/HISTORY OF SETI1959: Water hole suggested as best frequency range to search, by Giuseppi Cocconi and Philip Morrison1960: Project Ozma, Frank Drake searched Tau Ceti & Epsilon Eridani (nearby suitable stars)1961: Drake Equation & first meeting about SETI, ten attendees including Sagan, Drake, & Morrison1960’s: Many all-sky surveys carried out in Soviet Union1973-82: Horowitz, targeted ~400 Stars1974: Signal (lasting 3 minutes) sent by Arecibo radio telescope towards globular cluster M131983-85: Sentinel & Horowitz, all-sky survey1985-92: META, 8 million channels, funded by Planetary Society 1985-present: SERENDIP including SETI@home SETI@home (http://seti.berkeley.edu), “piggybacks” on radio telescopes that are performing other observations1992: NASA begins a SETI project1993: funding cut for NASA SETI project1994-present: Project Phoenix, targeted search carried out by SETI Institute, funded by private donations1995-present: Project BETA funded by Planetary Society. This search uses a multi-channel analyzer that can search 250 million channels simultaneously. The entire “water hole” frequency range can be searched in 16 seconds per star.RADIO WAVES FOR SIGNALSADVANTAGES:–NOT ABSORBED BY INTERSTELLAR DUST (UNLIKE VISIBLE LIGHT AND OTHER KINDS OF ELECTROMAGNETIC WAVES)–LOW ENERGY REQUIREMENTS, THUS CHEAP–TRAVEL AT THE SPEED OF LIGHT (LIKE OTHER ELECTROMAGNETIC WAVES, BUT FASTER THAN ANY SPACESHIP)–CAN CARRY A LOT OF INFORMATION (LIKE OTHER ELECTROMAGNETIC WAVES)LASERS FOR COMMUNICATIONS?A LASER BEAM IS TIGHTLY COLLIMATED (DOESN’T SPREAD OUT) – ENERGY CONCENTRATED IN A SINGLE DIRECTION.ENERGY ALSO CONCENTRATED AT A SINGLE WAVELENGTH – CAN OUTSHINE A STAR AT THAT WAVELENGTH.VISIBLE LIGHT (LASER) EASIER TO USE THAN RADIO WAVES OR MICROWAVES (MASER).MAY BE PREFERABLE TO RADIO COMMUNICATIONS IF DESTINATION IS KNOWN.SINCE SIGNAL IS TIGHTLY BEAMED, WE ARE LESS LIKELY TO INTERCEPT A SIGNAL ACCIDENTALLY.DELIBERATE VS. ACCIDENTAL SIGNALSACCIDENTAL SIGNALS ARE NOT DESIGNED TO ATTRACT THE ATTENTION OF ALIEN CIVILIZATIONS. THEY ARE USED FOR OTHER SURPOSES, BUT ESCAPE INTO SPACE AND COULD BE PICKED UP BY ALIENS.–EXAMPLES: OUR TV AND FM RADIO BROADCASTS, PLUS MILITARY RADAR SIGNALSDELIBERATE SIGNALS ARE DESIGNED TO ATTRACT THE ATTENTION OF ALIEN CIVILIZATIONS.DELIBERATE VS. ACCIDENTAL SIGNALSHOW STRONG ARE THE SIGNALS WE CAN SEND? ASSUMING THAT THE HYPOTHETICAL ALIENS WHO ARE DETECTING OUR SIGNALS HAVE THE SAME LEVEL OF TECHNOLOGY WE HAVE:–THEY COULD DETECT OUR TV AND FM RADIO BROADCASTS IF THEY WERE UP TO 1 LY AWAY (NO STARS THAT CLOSE).–THEY COULD DETECT OUR MILITARY RADAR SIGNALS IF THEY WERE WITHIN 30 OR 40 LY.–THEY COULD DETECT OUR DELIBERATE SIGNALS (IF SENT WITH ARECIBO RADIO TELESCOPE) IF THEY WERE ANYWHERE WITHIN THE MW GALAXY.IF THE ALIENS ARE MORE ADVANCED THAN WE ARE TECHNOLOGICALLY, THEY COULD DETECT OUR SIGNALS FROM FARTHER AWAY.DELIBERATE VS. ACCIDENTAL SIGNALSBUT WOULD THEY BE ABLE TO UNDERSTAND OUR SIGNALS?–IT WOULDN'T BE EASY IN THE CASE OF OUR ACCIDENTAL SIGNALS. WE HAVE AGREED ON CERTAIN WAYS OF ENCODING INFORMATION IN THESE SIGNALS THAT MAY NOT BE OBVIOUS TO SOMEONE ELSE (EVEN OTHER HUMANS). EVEN IF THEY COULD FIGURE THIS OUT, THEY WOULDN'T UNDERSTAND ANY HUMAN LANGUAGES OR UNDERSTAND HUMAN CULTURAL REFERENCES.–IN THE CASE OF DELIBERATE SIGNALS, WE WOULD HAVE TO TRY TO MAKE THE SIGNALS EASY TO UNDERSTAND.WHAT WILL A SIGNAL CONSIST OF?A SIGNAL THAT DOESN’T CHANGE WITH TIME CARRIES NO INFORMATION.INFORMATION CAN BE CARRIED BY CHANGING THE INTENSITY (AM) OR WAVELENGTH (FM) OF SIGNAL WITH TIME.BUT WHAT CONTENT DO WE WANT TO PUT INTO THE MESSAGE, AND HOW DO WE PUT IT THERE? HOW CAN WE INCREASE THE LIFELIHOOD THAT THE ALIENS WILL UNDERSTAND WHAT WE ARE TRYING TO SAY?REMEMBER THAT THE ALIENS WON’T KNOW OR USE ANY HUMAN LANGUAGES.WHAT WILL A SIGNAL CONSIST OF?WHAT CONTENT DO WE WANT TO PUT INTO THE MESSAGE, AND HOW DO WE PUT IT THERE?THEY WOULDN'T UNDERSTAND ANY HUMAN LANGUAGE.PICTURES?–HOW DO WE TRANSMIT A PICTURE USING RADIO WAVES OR LASERS? MATHEMATICS?–MATHEMATICS PROVIDES A UNIVERSAL LANGUAGE THAT ANY TECHNOLOGICAL CIVILIZATION WILL UNDERSTAND.–WE CAN USE MATH TO TRANSMIT A PICTURE.–BUT WHAT KIND OF MATHEMATICS?COUNTING IN BINARY AND DECIMAL0+0=0 1+0=1 1+1=2 2+1=3 3+1=44+1=5 5+1=6 6+1=7 7+1=8 8+1=9NOTICE THAT A NEW SYMBOL IS CREATED FOR EACH NEW NUMBER.UNTIL… 9+1=10, WHICH IS “NINE PLUS ONE IS TEN, BUT WRITE ZERO AND CARRY THE ONE.” A NEW SYMBOL IS NOT CREATED TO REPRESENT THE NUMBER TEN. IN THE DECIMAL SYSTEM, THERE ARE ONLY TEN DIFFERENT SYMBOLS (0, 1, 2, 3, 4, 5, 6, 7, 8, AND 9) USED.IN BINARY, THERE ARE ONLY TWO SYMBOLS (0 AND 1): 0 + 0 = 0 1 + 0 = 1 1 + 1 = 10 (10 = THE NUMBER TWO WRITTEN IN BINARY)10 + 1 = 11 (THREE) 11 + 1 = 100 (FOUR)…DECIMAL012345678BINARY0110111001011101111000DECIMAL vs. BINARY•IN DECIMAL, AN EXAMPLE IS 7205 •7205 = (7 x 1000) + (2 x 100) + (0 x 10) + (5 x 1) •7205 = (7 x 103) + (2 x 102) + (0 x 10) + (5 x 1)IN BINARY, AN EXAMPLE IS 10111011 = (1 x 8) + (0 x 4) + (1 x 2) + (1 x 1) 1011 = (1 x 23) + (0 x 22) + (1 x 2) + (1 x 1)1011 IN BINARY WOULD BE WRITTEN AS 11 IN DECIMALBINARY NUMBERSSIMPLEST SYSTEM – ONLY TWO SYMBOLS (0 AND 1) NEEDEDEACH SYMBOL (0 OR 1) IS A BITUSED BY MOST COMPUTERSWOULD BE AN OBVIOUS WAY TO ENCODE A MESSAGE–A PULSE COULD BE A “1” AND A GAP (NO SIGNAL) COULD BE A “0” (OR VICE VERSA)–A LONGER-DURATION PULSE COULD BE A “1” AND A SHORTER-DURATION PULSE COULD BE A “0” (OR VICE VERSA)–TWO DIFFERENT FREQUENCIES COULD BE USED – A PULSE AT ONE FREQUENCY COULD BE A “1”, AND A PULSE AT THE OTHER FREQUENCY COULD BE A “0”BINARY NUMBERSMESSAGE CAN ENCODE A PICTURE – LET 0 BE A WHITE DOT AND 1 BE A BLACK DOT (OR VICE VERSA)MUST ARRANGE BITS INTO ROWS AND COLUMNS IN AN UNAMBIGUOUS WAY–IF A MESSAGE CONTAINS 1200 BITS, THE DOTS COULD BE ARRANGED IN•30 ROWS, 40 COLUMNS (OR VICE VERSA)•60 ROWS, 20 COLUMNS (OR VICE VERSA)•120 ROWS, 10 COLUMNS (OR VICE VERSA)CHOOSE TOTAL NUMBER OF BITS IN THE MESSAGE TO BE THE PRODUCT OF TWO PRIME NUMBERS –FOR EXAMPLE, 551 = 19 x 29–BUT IS THIS 19 ROWS AND 29 COLUMNS, OR 29 ROWS AND 19