If humanity ever receives authentic signals from an alien civilization, should it respond? The question is not too preposterous to consider.

The U.S. government is expected to soon publish a report revealing what several of its entities, including the Central Intelligence Agency, know about “unexplained aerial phenomena” — that is, UFO sightings made over several decades by military personnel and others.

If alien civilizations exist, the chances we'll make contact, however small, are probably growing faster than ever before given advances in our ability to study planets orbiting other star systems, and to search with telescopes for signals indicating intelligent life. So far, nearly every such signal detected — mostly by research supported by the SETI Institute in California — has eventually been traced back to our own satellites or interference coming from other human activity. But one day — next week, in a century, maybe longer — that may change.

If we do actually hear from an alien civilization, should we send a message back? Stay silent? This issue has stirred argument among scientists, as any other civilization would most likely be far more advanced than our own. Some scientists urge sending out signals to initiate contact now; others think that’s far too risky. But this really shouldn’t be a decision for scientists alone — the entire world should be involved.

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