There may only be a few dozen full-time SETI researchers, but millions more want to offer some part-time help. Their interest is understandable. What, after all, could be more enticing to a person of the 21^st century than the thought that, despite the ingenuity of the tens of billions of humans that have strolled and lolled across this planet, he or she might be the first to discover aliens on some far-off world?

This widespread interest in aiding the search undoubtedly accounts for the popularity of the SETI@home screen saver. It also accounts for a lot of my e-mail.

Every day I get screenfulls of suggestions, questions, and commentary. Most are straightforward: the writer has a query about a specific aspect of SETI technology. For example, how can we recognize an extraterrestrial signal? Occasionally a correspondent will have a laundry list of questions that could more quickly be answered if they would only take a two-semester college course in either physics, astronomy, or radio engineering. My responses to such non-specific inquiries are probably unsatisfying, but I usually write something out of sympathy for those impeded by high tuition or low SAT scores.

Now and again, independent thinkers will send their own research papers - the distilled essence of years of effort in the attic or den - which purportedly show in a handful of pages, and with third-grade mathematics, that Einstein was wrong, and that SETI is therefore, somehow, barking up the wrong tree. I store these with tender care, and always offer to send back originals. But then again, I'm probably too soft.

Then there are the folks who have privileged insight, and want to share. "Check out the Pleiades with your antennas," they will admonish. Of course, the Pleiades comprise a young stellar cluster: its member stars are pups, only a few tens of millions of years old - hardly time enough to incubate complex life.

"The Sirius system," others recommend. "After all the Dogon (a tribe in Mali) were visited by aliens who told them about the white dwarf star that orbits Sirius A." Alas, Sirius, too, is a young star, at most a few hundred million years old. And the Dogon probably weren't visited.

Occasionally, I'll be contacted by "remote viewers," who apparently have the power to locate the extraterrestrials using nothing more than the hardware that squats between their ears. They, too, will offer targets in the sky (again, usually bright, naked-eye stars that almost invariably are too hot, and too young, to support interesting habitats for life). And while I'm always keen for new ideas, I fear that - given the cost in time and money to scrutinize any star system - targets need more supporting material than simply a "remote vision".

Another category of suggestion is how to do the experiment better. "Why are you wasting your time looking for light or radio signals?" some correspondents rebuke. "Gravity waves are what the aliens will be using to communicate, because gravity waves are instantaneous." Even leaving aside the considerable difficulty of detecting a gravity wave, and the even greater difficulty in generating one (you might have to smash stars together to signal distant listeners), there's the disappointing fact that, as far as we know, gravity waves travel at light speed, and no faster.

A variation on this theme, and one that is fashionably erudite, is to propose that advanced societies will chat using quantum entanglement, a subtle effect that is instantaneous. But a careful look at this phenomenon will show that it doesn't beat the light-speed rap. If you want to send information, quantum entanglement is not a scheme for doing so instantaneously.

At least a few people each month offer the "new physics" lament. "Two hundred years ago, people were still communicating by flashing lanterns and smoke signals. Those techniques were indescribably unsophisticated. So what makes you think that advanced societies would still be using primitive [their word] electromagnetic radiation to signal?" Well, of course there's no denying that new developments in physics might turn up communication schemes of which we are unaware - schemes that really do make light and radio seem like primitive ways to transmit messages. The problem here is that it's gosh-darn difficult to conceive an experiment - let alone built the required equipment - when you have no idea of the physical principles involved. This is like telling Christopher Columbus to forget the wooden ships, and build a jet plane.

Still others try to help us tune our receivers. The natural frequencies of DNA and chlorophyll have been suggested as spots on the dial to investigate (but what, exactly, are those frequencies?) Others say we should tune our equipment to the wavelength of brain transmissions (presumably alien brains). Well-intentioned suggestions, but hard to either justify or implement.

Clearly, much of the free advice we get is worth the price paid. But sometimes there are real solid ideas in this unsolicited input, and I honestly try to give each incoming bit of correspondence the benefit of consideration. The best ideas in science often arrive on unexpected trajectories, and that's certainly been true for SETI.

So keep those cards and letters coming, folks. Just don't expect a college education by e-mail.