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.

Are ridiculously crazy and complex ideas sometimes correct? Absolutely. Should we jump to the conclusion that they're correct without ruling out more vanilla explanations? Probably not. When it comes to UFOs, we might ask ourselves whether it is more likely that E.T. life exists, took an interest in us, traveled who-knows-how-far across the universe, buzzed through our skies, and then disappeared—or, more implausible still, crashed in Roswell, New Mexico? Or is it perhaps more likely that experimental military aircraft or poorly understood natural phenomena are responsible for things we see in the sky but can't identify?

Without "extraordinary" evidence, I'm going with the second option. That being said, most scientists I know (including myself) think that finding extraordinary evidence for E.T. life would be one of the most paradigm-shifting discoveries in all of human history. But we also have to be mindful of confirmation bias—the well-documented fact that the more we want something to be true, the more likely we are to believe it, and the less likely we are to apply a truly critical eye. But in fact, as I often tell my students, the more we want something to be true, the more critical we have to try to be. Or as Richard Feynman put it: "The first principle is that you must not fool yourself—and you are the easiest person to fool."

In my view, even if unidentified flying objects are terrestrial in origin, they warrant understanding. Hoaxes aside, studying genuinely unidentified objects could give us new scientific insights, or provide information on threats to national security. Just because something is unlikely doesn't mean it isn't worthy of serious academic study. In fact, I would argue that the more rare a phenomenon is, the more insight it is likely to give us into how things work.

Since 1947 there have been three (known) formal investigations into UFOs: Project Sign (1947­–1949), Project Grudge (1949–1951), and Project Blue Book (1952–1969). As part of Project Blue Book, the Condon Committee was convened in 1966, including such luminaries as the late Carl Sagan, and tasked with carrying out an independent analysis of available data on UFOs. Perhaps not surprising, but disappointing to many, the committee did not find that any of the UFO reports they examined required extraordinary explanations. It is, however, interesting to note that roughly 6 percent of the 10,147 UFO reports the U.S. Air Force investigated were classified as "unidentified." That is still over 600 cases.

Of these unidentified cases, the Condon Committee concluded that, "most of the cases so listed are simply those in which the information available does not provide an adequate basis for analysis." Some cases, however, raised eyebrows. For example, the Lakenheath-Bentwaters Incident, which took place in England in 1956, involved both the U.S. Air Force and the Royal Air Force. About this case, the committee reported, "in conclusion, although conventional or natural explanations certainly cannot be ruled out, the probability of such seems low in this case and the probability that at least one genuine UFO was involved appears to be fairly high." What actually happened? Who knows? This was over 60 years ago. Our scientific technology was far behind what it is now. Then again, so was our ability to pull off hoaxes.

Much of the problem with cases like Lakenheath-Bentwaters is that they are not repeatable. When something happens just once and never again, it is really hard to test our hypotheses—and the bedrock of the scientific method is that a hypothesis simply must be testable to be handled scientifically. Another famed example of a nonrepeating and unresolved case happened in 1977 with the "Wow!" signal. An extremely strong narrow-band radio signal was detected by the Big Ear radio telescope at almost exactly the frequency of a fundamental hydrogen transition line (1420.41 MHz), which we expect an E.T. civilization might use to communicate. Fast-forward 40 years, and astronomers identify a previously unknown comet that was passing by back in 1977 and could have accounted for the "Wow!" signal. Does this new discovery rule out an E.T. origin? Nope. But Occam's razor suggests that a comet that we know exists—and we know could have caused the signal—seems a tad more likely.

Extraterrestrial life was also on the table as an option in 1967 when Jocelyn Bell Burnell observed short radio pulses coming from a fixed location in the sky—and repeating. Because the pulses repeated, it was possible to rule out conventional explanations such as stars, or Earth-based emissions. As Burnell writes about the potential of E.T. life, "obviously the idea had crossed our minds and we had no proof that it was an entirely natural radio emission." With the E.T. hypothesis still on the table, the radio source was even nicknamed LGM-1 ("Little Green Men 1"). But the source did repeat, and more of these repeating radio sources were found, and hypotheses could be tested. What were these mysteries signals? Burnell had discovered pulsars, extraordinary dense and spinning remnants of supernova. While an E.T. life origin for the signals was ruled out, the discovery of pulsars has been of such importance to understanding our universe that they have resulted in two Nobel Prizes.

I will admit that our repeated failures to detect signs of E.T. is a downer. One reason this gets to me is because of something called "Fermi's Paradox." In a nutshell, given some basic assumptions about life, one could reasonably conclude that our galaxy ought to be teeming with it. So as Enrico Fermi famously asked: "Where are they?" There are three main categories of solutions: First, life could be really, really, really hard to get going. Our very limited evidence on Earth suggests this is not so; life arose on our planet almost as soon as it possibly could have. But a singular data point is not sufficient. We can't at present rule out that we are utterly alone in our galaxy, if not the entire cosmos. That is depressing.

The second class of explanations suggests that there is, in fact, E.T. life, but we just haven't detected it. That could be because we just haven't looked very hard yet, or because we are not looking in the right way, or because they don't want us to see them. Given the age of the universe and our galaxy, if life isn't super-hard to emerge, we are statistically most likely to be cosmic babies. In this context, E.T. life is likely to be millions of years more technologically advanced than we are. Thinking about how far our technology has come in the last 100 years, it is unfathomable to think what we might be capable of in a million. If we survive that long. If E.T. life is millions of years more advanced than we are, and they don't want us to know about them, I'm pretty sure we wouldn't know about them.

Then there is the third set of solutions to Fermi's paradox. These go along the lines of the following: Life has formed and evolved elsewhere. Maybe lots of times. But it doesn't exist now. There are lots of ways the universe could kill us, for example a major asteroid impact. If we were sufficiently technologically advanced, however, I give us a fighting chance. Or we might kill ourselves off. This is where Fermi's Paradox gets really depressing. We are in our technological adolescence, by which I mean we are smart enough to destroy ourselves, but maybe aren't smart enough not to do so. It could be that any civilization that becomes sufficiently technologically advanced is doomed to destroy itself.

For the time being, as far as we know, we are the only sentient life capable of trying to understand the universe. If we screw up, it doesn't look like anyone is going to come to save us. I kind of hope that E.T. life is out there, millions of years more advanced, and just waiting for us to grow up before it stops by for a visit. And I hope that headline actually makes the front page above the fold.