NSCI 314LIFE IN THE COSMOS16 - INTERSTELLAR COMUNICATIONDr. Karen KolehmainenDepartment of Physics, CSUSB http://physics.csusb.edu/~karen/HOW TO SEARCH FOR LIFE IN OTHER SOLAR SYSTEMS: TRAVEL OR COMMUNICATION?INSTEAD OF SPACESHIPS, USE PHOTONSADVANTAGES OF PHOTONS (LIGHT):–TRAVEL AT SPEED c (FASTER THAN ANY SHIP)–REQUIRE LESS ENERGY THAN SPACESHIPS–CHEAPER–CAN CARRY JUST AS MUCH INFORMATION–RISK OF BIOLOGICAL CONTAMINATION IS ELIMINATEDELECTROMAGNETIC SPECTRUMSPEED OF LIGHT c = 300,000 km/sc = 1 light year / yearFREQUENCY = NUMBER OF WAVES PER SECOND1 Hertz = 1 wave per second1 kHz = 1,000 Hz1 MHz = 1,000 kHz = 1,000,000 HzSPEED = FREQUENCY x WAVELENGTHLONG WAVELENGTH LOW FREQUENCY LOW ENERGYSHORT WAVELENGTH HIGH FREQUENCY HIGH ENERGYTYPEGAMMA RAYS X- RAYSULTRAVIOLETVISIBLE LIGHTINFRAREDMICROWAVETV & FM RADIOAM RADIOWAVELENGTHSIZE OF ATOMSIZE OF ATOMVIRUSBACTERIADUST1 cm1 m100 mFREQUENCYVERY HIGHVERY HIGHHIGHBILLION MHzMILLION MHz1000 MHz100MHz1000 kHzRADIO COMMUNICATIONADVANTAGES OF RADIO WAVES: NOT AFFECTED BY INTERSTELLAR DUSTLOW ENERGY COSTSLOW NOISE BACKGROUND HIGH INFORMATION CAPACITYTRAVEL AT THE SPEED OF LIGHT (LIKE ALL FORMS OF ELECTROMAGNETIC RADIATION)TYPES OF SIGNALSDELIBERATE SIGNALS: SENT IN HOPES THAT ANOTHER CIVILIZATION WILL RECEIVE THEMACCIDENTAL SIGNALS: USED BY THE CIVILIZATION FOR OTHER PURPOSES, BUT ESCAPE INTO SPACE INADVERTANTLYWHAT HAVE WE SENT?–SO FAR, WE HAVE SENT ONLY ONE SHORT (3 MINUTE DURATION) DELIBERATE SIGNAL–HOWEVER, WE ARE SENDING OUT LOTS OF ACCIDENTAL SIGNALSWHAT ARE WE TRYING TO RECEIVE?–SETI = SEARCH FOR EXTRATERRESTRIAL INTELLIGENCE (ONGOING)–SEARCHING FOR EITHER DELIBERATE OR ACCIDENTAL SIGNALSACCIDENTAL SIGNALS THAT WE ARE SENDINGTV AND FM RADIO TRANSMISSIONS HAVE BEEN LEAVING EARTH SINCE ABOUT 1940.THEY HAVE MADE IT A LITTLE OVER 60 LY IN THAT TIME (REACHED 2500 STARS).ANYONE WITH OUR LEVEL OF DETECTION TECHNOLOGY COULD DETECT US IF THEY ARE WITHIN 30 TO 40 LY.DOPPLER SHIFTS IN SIGNALS WOULD RESULT FROM THE EARTH’S ROTATION AND ITS ORBIT AROUND SUN.SIGNAL STRENGTH WOULD ALSO VARY AS VARIOUS PARTS OF THE EARTH ROTATE IN AND OUT OF VIEW OF THE OBSERVER.WE HAVEN’T DETECTED ANYTHING LIKE THIS FROM NEARBY STARS.BUT WILL WE CONTINUE TO BROADCAST MUCH LONGER?A “BROADCAST” SENDS OUT A SIGNAL IN ALL DIRECTIONS (ALTHOUGH IT IS NOT EQUALLY STRONG IN ALL DIRECTIONS). CABLE AND OTHER FORMS OF DIRECTED DELIVERY MAY BE REPLACING BROADCASTS. IF MOST CIVILIZATIONS PROCEED THIS WAY, THE FRACTION OF THE CIVILIZATION’S LIFETIME SPENT BROADCASTING MAY BE RELATIVELY SHORT.DELIBERATE SIGNALSRADIO WAVES ARE BEST (FOR REASONS GIVEN EARLIER). BUT WHAT FREQUENCY DO WE LISTEN AND/OR TRANSMIT AT? RADIO WAVES INCLUDE ALL FREQUENCIES BELOW 300 MHz (OR ALL WAVELENGTHS LARGER THAN 1 METER). ANSWER: FREQUENCIES BETWEEN A FEW HUNDRED MHz AND A FEW THOUSAND MHz ARE BESTWHY?DELIBERATE SIGNALSAT FREQUENCIES BELOW A FEW HUNDRED Mhz, THERE ARE RADIO WAVES EMITTED BY ELECTRONS IN STRONG MAGNETIC FIELDS (PRODUCED BY A VARIETY OF ASTROPHYSICAL SOURCES). THESE PRODUCE A LOT OF “NOISE” THAT WOULD COMPETE WITH A SIGNALFREQUENCIES ABOVE A FEW THOUSAND MHz ARE ABSORBED BY OXYGEN AND WATER IN EARTH’S ATMOSPHEREDELIBERATE SIGNALSSO RADIO WAVES WITH FREQUENCIES FROM A FEW HUNDRED MHz TO A FEW THOUSAND MHz ARE BEST. (THIS IS SLIGHTLY ABOVE THE FREQUENCY RANGE USED BY TV AND FM RADIO.)BUT THIS IS A LARGE RANGE, AND WE COULD SPEND A LONG TIME SEARCHING AT VARIOUS FREQUENCIES WITHIN THIS RANGE.IS THERE ANY “SPECIAL” FREQUENCY WITHIN THIS RANGE THAT MIGHT SEEM LIKE A NATURAL CHOICE?YES!DELIBERATE SIGNALS“SPIN FLIP” TRANSITION IN THE HYDROGEN ATOM : FREQUENCY = 1420 MHz, WAVELENGTH = 21 cm.BUT H ATOMS THEMSELVES RADIATE AT THIS FREQUENCY, PROVIDING BACKGROUND “NOISE” FROM 1419 TO 1421 MHz (SPREAD BECAUSE OF DOPPLER EFFECT) SO MAYBE SOMEWHERE NEAR (BUT NOT EXACTLY) 1420 MHz IS BEST.ANOTHER “LANDMARK”: 1721 MHz TRANSITION IN OH MOLECULE. ANY “TECHNOLOGICAL” CIVILIZATION WOULD KNOW ABOUT THESE FREQUENCIES.THE “WATER HOLE” IS THE FREQUENCY RANGE BETWEEN 1420 AND 1721 MHzTHE WATER HOLERANGE OF FREQUENCIES WITH MINIMUM BACKGROUND RADIO NOISEFREQUENCY RANGE FROM 1420 TO 1721 MHz1420 MHz IS AN EMISSION LINE OF H ATOM1721 MHz IS AN EMISSION OF OH MOLECULE RANGE IN FREQUENCY = 300 MHz = 300,000,000 HzCHOICE OF NAME:H + OH  H2O (WATER)MINIMUM LEVEL OF NOISE  “HOLE”EVOKES IMAGE OF A GATHERING PLACE FOR ANIMALS, SUGGESTING THAT MESSAGES FROM CIVILIZATIONS MAY BE GATHERED IN THIS FREQUENCY RANGESEARCHING THE WATER HOLEA CHANNEL IS A SMALL RANGE IN FREQUENCY (BANDWIDTH) OVER WHICH A SIGNAL IS TRANSMITTED OR RECEIVED, TYPICALLY ABOUT 0.5 HzSETI MUST SEARCH A RADIO “DIAL” OF 300,000,000 Hz300,000,000 Hz0.5 Hz/CHANNELGIVES 600 MILLION CHANNELS IN THE WATER HOLE!A LOT OF CHANNELS TO SEARCH!FORTUNATELY, MODERN RECEIVERS (MULTI-CHANNEL ANALYZERS) CAN SEARCH SEVERAL HUNDRED MILLION CHANNELS SIMULTANEOUSLY!SEARCH STRATEGIESTARGETED SEARCHPOINT RADIO TELESCOPE IN THE DIRECTION OF SUITABLE STARS AND LOOK FOR A SIGNAL.SKY SURVEYSEARCH WHEREVER THE RADIO TELESCOPE (WHILE IN USE FOR OTHER PURPOSES) HAPPENS TO BE POINTING, E.G. PROJECT SERENDIP.NOTE: ARECIBO RADIO TELESCOPE IS NON-POINTABLE. AS THE EARTH ROTATES, SEARCH SKY IN FRONT OF TELESCOPE.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 observations1988: NASA funds a SETI Project1990: Observations begin1993: NASA forced to kill 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”