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341 We have no basis for assuming that another technological civilization would welcome contact with us; nor do we have any basis for assuming that another civilization would be hostile. We simply don’t know how extrater- restrials would react to contact with humans. Do we live in a universe of cooperation and altruism, or in a universe of Darwinian competition? Might this vary from one intelligent species to another? Some think—or assume—that any extraterrestrial civilization that broadcasts its existence is likely to have peaceful intentions. What if some listeners do not? Our first deliberate message might reveal a great deal about the present level of our science and technology—and about our comparative weakness. Half a century without a clear signal implies either some degree of scar- city, or else a reticence on the part of aliens to broadcast at full strength. This lack of beacons should be at least somewhat worrisome, Brin con- cluded, especially to those who feel an urge to shout. The civilizations that survive may be the ones that do not call attention to themselves.” Given our ignorance, a certain degree of prudence may be in order. We have policy choices; we can make a conscious decision about what to do. We could limit Active SETI. We could even reduce the intensity of our normal leakage radiation (this process already is underway in radio and television broadcasting, although not yet in the use of military or planetary radars). Meanwhile, the operators of our noisiest technologies will con- tinue to make the choice for us, without a public policy debate. Which Signals Could Be Dangerous? The Earth already radiates extensive signals at certain wavelengths, but most are too weak to be detected at interstellar distances. The brightest are confined to narrow ranges of frequencies. Which are most likely to reveal our presence? One approach is to classify human-generated signals in three catego- ries: signals not sent in preferred directions, which could be described as including the Earth’s normal radio leakage; Active SETI signals sent in preferred directions; transmissions in reply to a signal from an extra- terrestrial civilization. Signals that are sent with no spatial or temporal preference are part of Earth’s normal background noise and may not be a problem. However, messages that are sent in preferred directions and that are long enough for the other civilization to confirm their origin—such as Active SETI messages—may be dangerous." The search is science and is properly the domain of scientists. Deliber- ately calling attention to ourselves is not science, but policy. Given our lack of knowledge about alien civilizations—and the potential negative consequences of contact—we may need to observe a The Prime Question