What do you say to a space alien? This question might not be the foremost puzzle in your life, but it was the subject of a lively two-day conference at California's SETI Institute this week.

Here's why: A decade of research by astronomers now suggests that a trillion planets dot the Milky Way. It takes a real Debbie Downer to believe that they're all as dead as the Equal Rights Amendment. Unless Earth is special beyond reason, you can confidently assume there are plenty of societies out there.

That doesn't mean that they'll come to Earth (or, as many believe, already have). Interstellar travel, despite what you've seen at the local multiplex, is hard. But we could easily get in touch via radio signals or flashing laser lights.

SETI — the Search for Extraterrestrial Intelligence — is already scanning the skies, looking for such signals. So far, they haven't found any. But some practitioners figure we should also transmit signals; that we should try speaking without first being spoken to.

Doing so would raise a lot of questions. For example, in which directions should you beam your broadcast, and how do you encode the message? In addition, there's the prickly argument over whether betraying our existence could lead to trouble.

All worthy of consideration. But this week's conference had a narrower focus: message content. If we decide to pick up the phone, what are we going to talk about?

To get as wide a range of viewpoints as possible, the conference organizer, the Institute's Director of Interstellar Message Composition Doug Vakoch, brought together an international crowd of anthropologists, philosophers, linguists, astronomers, archaeologists, social psychologists, journalists, and designers. As you might imagine, this inhomogeneous group frequently arrived at opposite conclusions despite starting with similar premises.

For example, what's the best way to make a message understandable to minds that might be organized in ways far different than our own? Some argued that any society with the kit necessary for detecting broadcasts from Earth will have mastered mathematics and chemistry. We should use these as touchstones to encode our messages. But try writing an essay about love or local government using only mathematical symbols, and you'll quickly discover that this isn't easy (and seldom poetic).

"Send the equivalent of a Rosetta Stone," was the cry of other participants. And after all, that does sound like a great way to help the aliens quickly learn some earthly language. Of course, the "stone" needs to have parallel texts with another language or two, but maybe you could substitute pictures — a kind of picture dictionary. Easy squeezy.

But a linguist precipitated on this parade by noting that — given the uncertainties about why Homo sapiens even has language (is it merely a talent conferred by a random genetic mutation that hit our species 150,000 years ago?), there's no guarantee that the extraterrestrials will be blessed with the gift of gab. They might not have language any more than we have a great sense of smell.

Which brings us back to pictures. Why not simply tell them about ourselves by sending images of artifacts? Time capsules are precedent, one participant noted. They're small collections of contemporary culture that are sealed, buried and sent to the future, if not into space. Clever idea, but if we send the Klingons the radio equivalent of a time capsule, do we put in everything? Do we tell them about our cruelties, and about poverty and war? Or is it better to only display our better natures?

A leitmotiv of the conference — one thing that just about everyone felt they could agree on — was to beware of anthropocentrism. Don't assume that the way we think or describe things will be the same for the extraterrestrials. Context and local knowledge are the frameworks of our daily lives, and it's easy to forget that these are peculiar to us, both in place and in time. The aliens will not get our jokes, our literature, or our reality TV. Their minds, presumably vast and deep, could be as different from ours as those of bats and beetles.

It's a tough problem, and my own contribution was to opine that — rather than wrestle endlessly with what we should say — we send it all. Or at least send a lot. I suggested that we transmit the contents of the Internet, or some large subset thereof, rather than offering up more "greeting cards" similar to those that have been bolted onto some of our spacecraft. Sure, there's a lot of silly stuff on the web — it's not curated, to use the language of museums. But it's wide-ranging, covers a lot of human activity, and is highly redundant. For example, the concept of "automobile" is present in descriptions, photos, and videos. That redundancy will help them — assuming they have the processing power — to figure out a lot of what we've sent.

In movies, the aliens are almost always fluent in colloquial American English. That's handy, and it eases the burden on both actors and audience. Communicating with these well-spoken beings from beyond Earth is a slam dunk.

But if and when we decide to send a shout-out to other worlds, we should first abandon the idea that the inhabitants of those distant locales have our mind set — or even a similar mind.