What would happen if we found out that we are not alone in the universe? Or, on the flip side, what would happen if we decided that we really were alone? Experts provided updated answers to those age-old questions, from a scientific as well as a religious angle, during a Sunday session at the American Association for the Advancement of Science's annual meeting. But one of the most intriguing questions had more of a personal spin: What would you ask E.T. if you had the chance?

First, here's some background:

Questions surrounding the possibility of life beyond Earth might get more serious sometime in the next quarter-century or so. Wesley Traub, chief scientist for NASA's Exoplanet Exploration Program, predicted that by 2030, five Earth-scale planets would be identified among the 100 closest star systems as worthy of being studied for signs of life. He based that prediction on the most recent lineup of candidates from NASA's planet-hunting Kepler probe.

"About a third of all planets are planets that could have life on them," he said — that is, Earth-size worlds or super-Earths.

Looking for alien life
What would scientists look for when it comes to life detection? Traub speculated that future spacecraft could analyze the atmospheres of alien worlds for signs of high oxygen levels and water vapor. Spectral analysis of the light reflected by those planets might even turn up the chemical signature of chlorophyll or other chemicals indicative of life. But it'd be almost impossible to tell whether the alien organisms are one-celled creatures, six-legged dinosaurs or intelligent species. If they're smart enough to communicate with us, the only way we'd know is through well-known means such as radio signals or laser bursts (or maybe orchestrated blasts from a stellar beacon).

Seth Shostak, senior astronomer at the SETI Institute, has said that evidence of alien life — either through such direct contact or through long-distance chemical analysis — could become available in a time frame ranging from 2025 to 2035. And he bet his listeners at Sunday's talk that he'd buy them a cup of coffee if E.T. wasn't found in their lifetime. (Will that bet ever pay off? Think about it: You can't take your Starbucks with you.)

So what would society do if life is detected? At Sunday's talk, science historian Owen Gingerich said the first scientific claims for E.T.'s existence would likely be hotly contested, just as the Mars meteorite microfossils have been for the past 15 years. Even if the findings are confirmed, it would take years for the implications to sink in.

Most of the leaders of the world's religions say extraterrestrial life wouldn't shake their faith. But 16th-century theologian Giordano Bruno was burned at the stake after saying so, and even today some believers say E.T.'s existence would make a "mockery" of Christianity. Like it or not, religious institutions and other pillars of society would have to accept (or deny) a paradigm shift at least as big as the shifts sparked by astronomy and biology. 

Misanthropic principle
What if life is not detected? It's pretty hard to prove a negative, but suppose future probes analyze the atmospheres of scores of Earth-size planets ... and find nothing worthy of note. Suppose the search for extraterrestrial intelligence continues for a century ... and no messages are received. Howard Smith, a senior astrophysicist at the Harvard-Smithsonian Center for Astrophysics, said the evidence already suggests that intelligent life is extremely rare in the universe, and we're the only sentient beings within a 1,250-light-year radius. (Smith chose that figure because it's about as far as humans could possibly travel during a 100-generation round trip at the speed of light.)

"We are probably alone and will have to solve our own problems," he said at Sunday's talk.

Smith calls this the "misanthropic principle." That term plays off the widely cited anthropic principle — the idea that Earth appears to be so suited for life as we know it not necessarily because God made it that way, but simply because we wouldn't be around to see it if it wasn't.

The way Smith sees it, the misanthropic principle is a good thing. The view that we alone are responsible for our zone of the cosmos should make us feel "blessed," and more careful about not spoiling the good thing we've got here.

"The misanthropic principle is joyous," Smith said. "We should rejoice in our good fortune."

Is it depressing or liberating to think that we're truly the best the universe has to offer, at least in this celestial neck of the woods? Feel free to add your comments below.

Oh, and about the question we started out with: What would you ask E.T. if you had the chance? This came up during the question-and-answer session, and one of the suggestions was along the lines of "Dear E.T.: Do you have a religion?" (That led science writer David Despain to quip in a Twitter comment: "Hello, I'm a Jatravartid. Let me share with you the message of the Great Green Arkleseizure's white handkerchief.")

Personally speaking, I'd rather ask: "How did you do it? How did you survive long enough to get to this point of contact?" If E.T. responds by raising its ray gun, I'd probably have the answer I wasn't hoping to get.

But what would you ask? 

More about the search for aliens:

• How would alien life change your life? 
• What to do if we find alien life
• Calculate the odds of finding E.T.
• Hawking: Aliens may pose risks to Earth
• Still more about the search from msnbc.com

Join the Cosmic Log community by clicking the "like" button on our Facebook page or by following msnbc.com science editor Alan Boyle as b0yle on Twitter. To learn more about Alan Boyle's book on Pluto and the search for planets, check out the website for "The Case for Pluto."