Ifextraterrestrials ever phoned us, they would be more likely tosend narrowly directed bursts than constantly blaring signals? more text-messagingthan novel-writing, some scientists now suggest.
Sucha strategy also would be more practical for anyone on Earth toreach out to aliens ? if one had at least a billion dollarsto spend.
Howcheap is talk?
For50 years, people have watched the skies with radio telescopes,hoping to detect signals of intelligent alien life. So far, however,the effortsof SETI (the search forextraterrestrialintelligence) haveproved fruitless.
Nowsome scientists suggest the kind of signals SETI has hoped tofind for decades might not be what aliens would broadcast. In a way,the formof communication might come down to cost.
"Ourgrandfather used to say, 'Talk is cheap, but whiskeycosts money,'" said researcher GregoryBenford,an astrophysicist at theUniversity of California, Irvine, and an award-winning science fictionnovelist. "Whatever the life form, evolution selects for economy ofresources. Broadcasting is expensive, and transmitting signals acrosslight-years would require considerable resources."
Assumingthat aliens would strive to optimize costs, limit waste and make theirsignaling technology more efficient, Benford and his twin, James ? afellowphysicist who specializes in high-powered microwave technology ?suggest the signalswould not be steadily blasted out in all directions. Extraterrestrialswould bemore likely to send narrow "searchlight" beams delivered in pulses.
"Thisapproach is more like Twitter and less like 'War and Peace,'" saidJamesBenford, founder and president of Microwave Sciences Inc., inLafayette, Calif.TheBenford twins, along with James' son Dominic, a NASAscientist, detailed their findings in two studies appearing in the Juneissueof the journal Astrobiology.
TheBenfords suggest a continuous signal blared at thousands of stars wouldsimplycost too much energy. They say aliens might use short bursts ? say,anywherefrom a second to an hour long ? and point these signals in narrow beamsat onestar and then another in a cycle involving up to thousands of starsthatrepeats over days or years.
Forcivilizations that constantly watch the skies, the bursts would conveyenoughdata to be recognized as undeniably artificial. As observantcivilizations concentratedon this simple beacon, other beacons could broadcast more complex dataat lowerpower (assuming the aliens were still pursuing a frugal strategy).
TheBenfords suggested looking at a broad range of radio signalsin the 1- to 10-gigahertz range, where the travel of light isrelativelyunimpeded by interstellar matter. Currently SETI is focused on just the1-to-2 gigahertz region,where components of water such as hydrogenand hydroxyl (a compound of hydrogen and oxygen) emit radio signals.
"Theidea is actually based mostly on how all the electronicsof the 1960s, when SETI was first starting out, only operated in therange of afew gigahertz," Gregory Benford explained. "Now they operate in arange of up to 100 or 200 gigahertz, so it's a reason to revisit ourassumptions. Looking to 10 gigahertz makes sense, since it's cheaper byafactor of 10 to build a transmitter at 10 gigahertz than at 1gigahertz."
TheBenfords also said that instead of gazing at stars within 500 or solight-years,as most SETI efforts have done for decades, observers should point moretoward ourgalaxy's center to distances up to 1,000 light-years from Earth, where90percent of the galaxy's stars are clustered.
"Thestars there are a billion years older than our sun, which suggests agreaterpossibility of contact with an advanced civilization than does pointingSETIreceivers outward to the newer and less crowded edge of our galaxy,"Gregory Benford said.
Althoughthe galactic center is home to many bursting stars whoseexplosions are expected to sterilize the space around them, "the vastbulkof stars in the 28,000 light-years between Earth and the galacticcenter arenot in sterilizing environments," Benford told SPACE.com. "For ananalogy, you wouldn't want to hang out in Times Square all the time,but if youlive in New Jersey it's obvious that Manhattan is the place to look fortheaction."
"Willsearching for distant messages work? Is thereintelligent life out there? The SETI effort is worthcontinuing, but ourcommon-sense beacons approach seems more likely to answer thosequestions,"Benford said.
Havewe seen a beacon?
Onepossibility of an extraterrestrialbeacon is a puzzling transient radio source some 26,000light-years fromEarth that was discovered in 2002 in the direction of the galacticcenter. Itsends out radio waves in bursts lasting up to 10 minutes in a 77-minutecycle.
Scientistshave suggested the source, labeled GCRT J17445-3009, is a flare star,anextrasolar planet, a pulsar or a brown dwarf, but none of theseexplanationsfits well, the Benfords said.
Basedon the burst length and the short cycle, the Benfords doubt GCRTJ17445-3009 isa beacon aimed at possible civilizations among a large crowd of stars.Still,if GCRT J17445-3009 is artificial in nature, it could be a signal thatalienspointed just at us, having detected signs of life from our planet. Ifthat isthe case, the Benfords said, we may want to pay closer attention to itssignalsto look for hidden details.
Onthe other hand, GCRT J17445-3009 could be one link in an interstellarcommunications network. If so, it would make sense to look in theoppositedirection, to see if another beam was communicating at it.
"Westudied GCRT not because wereally think it's abeacon, but because it's an interesting way to look at similar burstingsources," Gregory Benford said. "There's thefamous 'Wow' signalfrom 1977, for instance, thatinvolved an enormous amount of power, and that there's still no goodexplanation for."
Insteadof just searching for extraterrestrial intelligence, theBenfords also considered messagingto extraterrestrial intelligences,or METI. They calculated that agalactic-scalebeacon, with an antenna roughly a half-mile (0.9 km)wide with a range of a little more than 1,000 light-years, could bebuilt for $1.3billion. It would cost $200 million annually to operate. To workeconomically,it would use only narrow, high-power microwave beams and 35-secondbursts aimedat each target star.
"Ofcourse, if you want to send a message, first you have tofind a billionaire for this," Gregory Benford told SPACE.com. He notedhehas spoken with a number of billionaires, including former Microsoftchieftechnology officer Paul Allen and Amazon.com founder Jeff Bezos, "andeveryone has the same remark ? that they would rather spend a billiondollars adifferent way."
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