The Harvard photon bucket isn’t looking at any particular wavelength, but SETI investigators have long speculated that intelligent beings would choose to send their signals at a special frequency, one that is somehow fundamental to the universe. If we knew what that frequency was, it would narrow our search dramatically, because we’d have to observe just a tiny fraction of the spectrum. That’s why Project Serendip and a number of other radio SETI efforts focused on the hydrogen line.

In the optical regime, there are equally interesting frequencies that an intelligent civilization might choose. Called Fraunhofer lines, these are naturally occurring gaps or holes within the spectrum of visible light given off by stars. At these frequencies, the stars’ background energy drops considerably—in some cases, to only one-tenth its normal value. So if an alien sent a signal at the wavelength of a Fraunhofer line, the transmitter wouldn’t have to be nearly as strong, and at the receiving end, the search for the correct wavelength would be greatly simplified.

The operators of the Harvard telescope assume that the transmitter is pointed our way continuously. But what if the source is transmitting only sporadically—pointing toward our solar system for a few nights, say, and then moving on to another star system? Only a lucky coincidence would have everything lined up at exactly the right time. Yet, the only way to cover the entire sky at once would be to construct many thousands of receivers, each looking in a different direction.

And what if the alien’s signal requires a much larger receiver than what we currently have? There are several options here. You can simply build a bigger photon bucket, which would increase the collection area and thus boost the number of incoming photons. Or you could network together lots of smaller telescopes. Stuart Kingsley, an optics engineer and SETI enthusiast, and I proposed such a scheme several years ago. We were inspired by the enormous popularity of the SETI@home program, which is harnessing the power of 5 million personal computers to crunch through the data collected by SETI radio telescopes.

Our proposal involved using hundreds or even thousands of amateur telescopes, equipping each of them with a low-cost photodetector and then aiming all of them at a given star system at the same time. Of course, each telescope would be a slightly different distance from the star, but you could compensate for those differences by using a GPS receiver to pinpoint each telescope’s position to within a few centimeters. You would also need an Internet connection to some central control center, which could collect all the data and coordinate when the telescopes were observing and where they were pointed.

For the best observations, though, you would need to place your telescope out in space. Earth places some limits on how sensitive a detector you can build. Manufacturing and maintaining a telescope’s large mirrors is costly, and wind vibrations and the pull of gravity also constrain the size of the apparatus. What’s more, the atmosphere filters out photons of certain frequencies, and you can’t observe at all in cloudy weather.

A photon bucket out in space or on the moon, by contrast, would experience low gravity and no wind (although the solar wind is still a consideration). You could therefore construct it from lightweight materials, so it could be much larger than any terrestrial receiver. And, of course, there would always be clear weather.

Such endeavors, though, will have to wait for a generous benefactor to come along. Nearly all of the SETI research today is funded by individual donors or by nonprofit groups, such as the Planetary Society, in Pasadena, Calif., and the Bosack/Kruger Charitable Foundation, in Natick, Mass., both of which helped finance the new Harvard facility. The U.S. government officially ended its support of SETI in 1993. Unless we get very lucky, we will need to conduct larger-scale, dedicated searches, not just in the RF and visible light spectrum but at infrared and ultraviolet wavelengths, too. We are, in other words, still a long way from being able to declare SETI a success or a failure. But broadening the scope of the search beyond radio waves is a significant step forward.