I get lots of interesting emails, but among last week's crop, this one stood out:
"What do you think of Professor Stephen Hawking's comment that we should stop trying to contact aliens, since if they come here it would be very bad for us? Do SETI scientists not consider this possibility or do you just want to be famous - or rather infamous - for causing the end of humankind? For God's sake, stop it immediately."
Let me state clearly and unequivocally that I am not inclined to cause the end of humanity, even if doing so does offer some modicum of short-lived notoriety. Let me also state an obvious rejoinder to this correspondent's concern: Our SETI experiments are passive. We listen. We don't transmit. There's no danger in simply trying to pick up a signal.
Nonetheless, Hawking's comment has many people legitimately asking: If SETI detects an extraterrestrial transmission, will someone grab the microphone and reply? If so, who speaks for Earth? Will that be whoever wields the most kilowatts? A group designated by international consultation? Or simply those who transmit first?
I doubt it makes any difference. After all, did it matter which of the Australian Aborigines first talked to Captain Cook?
Who responds and what they say is of less import than deciding whether we should reply at all, since the danger is in simply betraying our presence, not in the fine points of the message. It's naivete of a rare sort to think that if I'm hunting for pheasant, it will matter what the birds squawk at me.
In other words, if the extraterrestrials don't cotton to sentient neighbors, it's bizarre to think they will be dissuaded from doing something horrid simply because we had international discussions on what to say to them.
Of course, you could argue that there's no need to worry, since advanced aliens, able to communicate across the vast voids of space, will be benevolent, enlightened beings for whom aggression is as archaic as using trepanning to treat a migraine. Carl Sagan once suggested this, and maybe it's true. Then again, maybe it's not. We don't know.
Consequently, it's tempting to opt for the safest course, and forbid all high-powered transmissions towards the source of a SETI detection. That way, even if the chance of calamity is small, we won't have gambled our very existence.
But that would be hard to enforce, short of war. Besides, it doesn't matter: It's already too late.
Evidence of our existence has already washed over about 15,000 star systems, as the FM, television, and radar signals that were first transmitted during the late 1930s wick into space.
That isn't news to many, of course, but maybe this is: These signals are not hard to find. If there are any aliens within a few hundred light-years, these clues to our existence could be found with an antenna the size of Chicago. For any society able to threaten us across such distances, that's a pretty easy construction project.
And there's more. If hostile aliens can direct their battle rockets our way - a distance of thousands of trillions of miles - then they can surely place some telescopes at a mere 0.02 light-years from their home. Doing so would allow them to use their own sun as a gravitational lens to study the cosmos. They would be able to trivially find our leakage signals, and even the street lights of our cities.
Put another way, our unintended signals to the stars will be clearly visible to any societies that are capable of threatening us. Easy evidence of Homo sapiens is already out there. To forbid high-powered replies (or even deliberate inquiries) is bolting the barn door after the horse has cantered into the countryside.
In addition, prohibiting transmissions is not a minor matter. It's medicine we would need to take forever. After all, the requirement is not that we make ourselves invisible today, but endlessly. And that would be a sad legacy for those to come.
The bottom line is simple: Worrying about beaming signals towards the sky is both alarmist and useless.
I hope some of my email correspondents can now breathe easy.