What is it about unidentified flying objects and extraterrestrial visitors that holds such allure? Surveys consistently show that about a third of all Americans think alien spaceships are real — and that as much as 10 percent of the population have seen such spaceships. Eyewitnesses abound, but the physical evidence is flimsy.
"Why is the evidence so poor?" said Seth Shostak, senior astronomer at the SETI Institute and director of the Center for SETI Research. "One really good case might clinch it for them."
Shostak definitely thinks there's intelligent life out there. Otherwise he wouldn't be spending so much time and energy on the radio-based search for extraterrestrial intelligence, a.k.a. SETI. But he also spends more than his share of time debating people who are certain the aliens are already among us. Shostak encountered one such true believer during a speaking engagement in Chicago.
"One guy stood up and said, 'You're just a mouthpiece for NASA!'" Shostak recalled. "And I said, 'If that's true, don't they owe me some back pay?'"
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Fermilab physicist Don Lincoln has also puzzled over society's fascination with extraterrestrial life — and wrote a book about it, titled "Alien Universe."
Among the subjects he covers are the long-term projects to find traces of microbial life on Mars or elsewhere in the solar system, or identify potentially habitable planets beyond our solar system, or pick up radio signals from E.T. But he also traces how our fascination with aliens has changed through the years. For example, we're more likely to think of aliens as weirdly altered humans — like the little green (or gray) men of "X-Files" fame or the pointy-eared Mr. Spock from "Star Trek."
"When we talk about the more intelligent extraterrestrials, we're really holding a mirror up to ourselves," Lincoln said. "If we didn't see ourselves in the vision, we wouldn't find them nearly as fascinating."
But what about all those eyewitness reports? Lincoln said such reports don't cut it, even if they're attributed to presidents or generals. "With something like this, which would have such breathtaking consequences for our understanding of the universe, we're going to need something more than 'somebody said so,'" he said.
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And what about all those unexplained phenomena, like 2012's sightings of an object buzzing over Denver? Just because someone can't explain why an object is behaving in a particular way, doesn't make it an example of alien technology, Shostak said. "That's an argument from ignorance, and that's not good," he said. (By the way, the buzzing objects in the Denver video look a lot like bugs caught on camera.)
Shostak said the UFO community has "its own iconography, its own lore," and even its own belief that it's being held back by a vast conspiracy. John Podesta, who left his post as a senior adviser in the Obama White House last month, added fuel to the fire when he said in a tweet (perhaps in jest) that his biggest failure of the previous year was "once again not securing the disclosure of the UFO files."
Is the UFO debate a matter of science, politics ... or faith?
"People have accused SETI of being some sort of religion," Shostak acknowledged. "But maybe you could make that argument about the UFO community."
Shostak and Lincoln will discuss the alien conspiracy and other aspects of the UFO phenomenon with NBC News' Alan Boyle on Wednesday's installment of "Virtually Speaking Science," an hourlong talk show airing at 8 p.m. ET via BlogTalkRadio. You can also watch the show as part of a live virtual audience in the Exploratorium's Second Life auditorium. If you miss the live show, never fear: You can always catch up with the podcast in BlogTalkRadio's archive or on iTunes. February's show featured Don Lincoln previewing the restart of the Large Hadron Collider.
For still more about the search for aliens, check out Lincoln's book, "Alien Universe: Extraterrestrial Life in Our Minds and in the Cosmos"; or Shostak's book, "Confessions of an Alien Hunter: A Scientist's Search for Extraterrestrial Intelligence."