(CNN) -- Stephen Hawking's new documentary premiered Sunday night on the Discovery Channel. In it, he claimed that intelligent alien life almost certainly exists and that the search for it is valuable. He also suggested that the potential threats posed by contact with alien intelligence should discourage us from actively sending out messages to the cosmos.
As anyone who has seen the Discovery Channel broadcast knows, it did an excellent job of explaining astrobiology and the search for extraterrestrial intelligence. It illustrated how vast the search is (and will become) and its potential impact on Earth's inhabitants.
We earthlings are fairly new at technology (100 years of transmitting electronic signals) in a very old galaxy (10+ billion years). The SETI Institute's optical and radio searches can only detect life capable of technology more advanced than ours. If such life is less advanced, their technology will not be detectable across the huge distances of interstellar space (smoke signals don't get very far!).
The ultimate success of SETI also depends upon the average longevity of technologies (assuming there are others out there besides ourselves). Longevity or "L" is the last term in the Drake Equation, a formula designed to estimate the number of communicative civilizations in our galaxy. In fact, the length of time a technologically advanced species might continue to transmit is completely unknown and unknowable until, or unless, contact is made.
I think that Prof. Hawking made the point that a short-lived technological society (a small value for "L") means little chance of contact. But it L is large, it is likely that SETI searches will succeed and that the civilization that's transmitting is using a technology that is older and more advanced than our own. Of course he's right, but there's a lot of room for different opinions about what contact with an advanced technology would mean.
In describing the search for extraterrestrial intelligence, Prof. Philip Morrison (co-author in 1959 of the first scientific SETI paper) was fond of saying that "SETI is the archaeology of the future." It's archaeology because any signals we detect will tell us about their past (even signals traveling at the speed of light can take up to 100,000 years to cross the Milky Way Galaxy), but the successful detection would tell us that we could have a long future.
In that case, we are talking about contact through electromagnetic communication. What about physical contact? Well, one thing is for sure: If they can get here, then their technology is superior to ours, and not just by a little! Arthur C. Clarke's third law is, "Any sufficiently advanced technology will be indistinguishable from magic."
Can we be certain that their magic would do us harm? I would hope that Hawking would agree that a large value for L (a requirement for that magical, star-spanning technology) could also mean that their distant civilization had found a way to stabilize itself in order to survive and grow old. That might require outgrowing any aggressive and belligerent tendencies that may have characterized their youth.
Such an advanced technology might well send explorers whose size and shape we cannot yet imagine to study and examine the diversity of life that evolved elsewhere -- and rather than exploiting us, they might value and support the natural biodiversity of the galaxy.
Indeed, most of Hawking's Discovery Channel program was devoted to explaining that life as we know it is hugely diverse, and life as we don't yet know it is worth searching for because of all the ways a discovery would inform and surprise us.
At SETI, our current mission isn't to broadcast, but rather to listen to the universe and see what else might be out there. If signals are detected, everyone on the planet should have a voice in deciding how to respond.
The opinions expressed in this commentary are solely those of Jill Tarter.