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183 make a conscious decision not to seek it. If they ever tried to detect other civilizations, they may have given up after a search for signals or a search with probes failed to reveal convincing evidence; very few species may have millenium-length attention spans. They may see no point in exploring their interstellar environments or expanding their presences outward into the Galaxy; they may think that such tasks are beyond them or too low a prior- ity to warrant a serious effort. They may have abandoned the use of the needed technological capabilities because of internal crises or societal changes. Perception does not necessarily lead to action. Motivation may be as important as capability. If other civilizations do search for signals or send out probes, they have not found us yet. We may have entered the era of interstellar communications so recently that they have not detected us. If they have found us and have decided to respond, their messages or probes may not have reached us. There are alien signals or artifacts, but they are beyond our ability to detect. Other technological civilizations may be using means of communi- cation or transport unknown to us. There are alien signals or artifacts that are potentially detectable with our present technologies, but we do not see them because they are outside of our current search space. We may not have searched long enough, widely enough, deeply enough, or continuously enough. We may be looking for the wrong kinds of signals or artifacts; our searches may rest on faulty assumptions. We have detected signs of extraterrestrial technology but fail to recognize them. We may have evidence that is unpersuasive or ambiguous, or the evidence may be buried in masses of recorded data. Other technological civilizations are concealing their presence from us, and possibly from others as well. They may deliberately limit their emis- sions, maintaining something like radio silence. Explanations Common to Both New Arrival Inadequate Human Technology Inadequate Search Strategies We Misunderstand the Evidence They Are Hiding