Making the Search Simple

Could SETIefforts be simpler? While today's radio searches rely on highly sophisticatedantennas and receivers, our fledgling optical search systems are far lessintricate. Experiments to look for fleeting flashes of light from other starsystems have been conducted using only a modest telescope and about 20 thousanddollars' worth of electronics; simple and cheap, like onion dip.

But there'sa problem: these searches for momentary pulses of light check only one part ofthe sky at a time. Therefore, unless some alien society is incessantly aimingtheir lasers in our direction, there's a distressingly good chance that we'llbe looking the wrong way when our solar system gets pinged.

This isknown in the SETI trade as the "synchronicity problem." I was recentlythinking about it over a fourth-rate burger, when it reminded of a passingremark once made by California radio astronomer Jack Welch, offered at a SETImeeting in Paris two dozen years ago. Welch wondered whether any gregariousextraterrestrials might not make a signal so strong and obvious that "even cowscould see it."

Despite theimportant fact that cows seldom write for refereed journals, Welch's point isworth ruminating over: why couldn't an alien civilization aim a signal at Earththat we could detect simply by pivoting our eyeballs to the night sky?

Indeed,this type of signal might make sense as part of a two-component transmittingstrategy, something I've broached in these electronic pages before. Onecomponent is an intermittent, powerful "ping" designed to mark a spot on thesky and get our attention. Having found it, we would surely expend the time andcurrency to build whatever instrumentation was necessary to detect the secondcomponent, the (far weaker, but always on) "message."

Historically,intermittent lights in the sky have frequently grabbed our attention. Supernovae are an example. Probably the brightest in recorded history (as seenfrom Earth) occurred in the year 1006, and was a favorite subject at elite cocktailparties for months. Then five centuries later Tycho Brahe, the celebratedDanish astronomer with the metal nose, saw a "guest star" in the constellationof Cassiopeia. It shone as bright as Venus, and eventually gained notoriety asTycho's Supernova.

True, youraverage Renaissance man-in-the-street probably didn't remark on Tycho's find. Butit was enough that a few people did. They made it known to everyone, andforever.

So imaginethere was an occasional, very bright light in the night sky-appearing at leastas frequently as once a year-something that we could see easily, even without atelescope and 20 thousand dollars' worth of electronics. A few tens ofbillions of people have trod our planet since Homo sapiens emerged, andit seems pretty certain that this intermittent flash would not only have beennoticed many times - it would be written into our folklore, and as familiar asthe evening star.

Yet wedon't seem to have witnessed such a thing. Is this because it's too hard forthe aliens to arrange? Does it require too much energy for them to light upour sky this way?

Let's lookat the numbers. Virtually everyone (including cows) has observed the strobelights affixed to airplane wing tips. You can easily see these at anyaltitude, but when a jetliner is only a mile high, the strobes are muchbrighter than the brightest star. They flash about once a second, at anaverage power of roughly 50 watts.

So whatwould it take to make a similarly noticeable flash once a year from, say a thousandlight-years away - a reasonable maximum distance for the nearest aliens?

For thosereaders who love the requisite arithmetic, I note that a thousand light-yearsis about 6 thousand trillion miles. Ergo, the average power necessary for aonce-a-year flasher that, at Earth, would be as bright as a mile-high jetlinerstrobe, is 5 10²⁵ watts. That's trillions of times morepower than all humans use; trillions of times the sum total of every lightbulb, factory, SUV, and Wii. In fact, it's 10 percent of the power output ofthe Sun.

But perhapsI should say, it's only 10 percent of the power output of the Sun. Forsome advanced aliens, that might not be very consequential. In 1964, Russianastrophysicist Nikolai Kardashev theorized that the universe could be host tocivilizations on three levels: Type I societies that use the energy resourcesof their planet; Type II that use most of the output of their home star; andType III societies that command the energy output of an entire galaxy.Civilizations falling into either of the latter two categories would have theresources to make our theoretical galactic flasher.

So does thefact that naked-eye SETI has failed to find such a beacon mean something? Arewe on the horns of a dilemma? It sounds as if we've somehow missed seeing sucha signal, or perhaps there's no nearby civilization with the technical talentsto construct one. The latter would suggest that there's nothing moreaccomplished than a Type I society in our neck of the woods, despite the factthat the Milky Way is 10 billion years older than Earth.

That's possible.Then again, maybe the truly sophisticated aliens have better means of tellingus where to find information. Or perhaps they have sound reasons to be at leastslightly cryptic.

Still, itstrikes me as paradoxical, given the vastness of the cosmos, that such a simplesignal has not been recognized, a signal that even a cow could see. No lasersfor our grazers. Call it the cow paradox.

• All About SETI
• Shadows and Silhouettes: Looking for Transits
• Images: Venus Transit Gallery
• Detecting Other Worlds: The Transit or 'Wink' Method
• Way-Out World: New Technique Finds Most Distant Planet Ever
• Mercury Transits Sun, Images on Web