For more than a half-century, a small group of astronomers has sought intelligent company among the stars. They’ve done so by turning large radio antennas skyward, hoping to eavesdrop on signals from an advanced society. It’s a program known as SETI, the Search for Extraterrestrial Intelligence.

But now some researchers propose that we should do more than simply don headphones and await E.T.’s call: We should make serious efforts to encourage a response from putative aliens by deliberately transmitting our own messages. It’s a simple idea, akin to tossing a bottle into the cosmic ocean. But recent arguments for what’s termed active SETI have loosed a storm of controversy, one that has even washed into the halls of academe.

Why is this? Why has the sending of dispatches to worlds many trillions of miles distant suddenly become a hot-button issue? The simple answer is that there’s now a perception that advertising our existence could be a mortal threat to the planet.

The reasoning is this: While no one has yet offered decisive proof for life beyond Earth, in the past two years astronomers have learned that tens of billions of habitable planets suffuse our galaxy. Consequently, to believe that only Earth has spawned intelligence is to insist that our world is the site of a miracle. That point of view rarely appeals to scientists.

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