It barely got a mention in the media, but in June the U.S. Navy briefed members of Congress on UFOs. The fact that we live in a culture where this is only a minor news story gives me pause; if someday extraterrestrial life actually visits Earth, the story will least make the top 10 list of "Most Significant Things That Have Happened in Human History." To be fair, the briefing was classified, so we don't actually know what Congress was told. But according to a 2015 survey, 56 percent of Americans already "believe" in UFOs, regardless of what Navy pilots may or may not have seen.

For many people, "UFO" is synonymous with aliens, but it's worth reminding ourselves that it literally stands for "unidentified flying object." An unidentified object could be just about anything, because … well, it's unidentified. One of our mottos in science is that "extraordinary claims require extraordinary evidence." This doesn't mean that crazy-sounding things are never true; it means that we should practice due diligence when thinking about overturning well-understood or well-tested ideas. This motto also suggests we keep an eye on Occam's razor—the idea that the simplest explanation is the most likely to be true.

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