Despite offering only one sentence on the subject, Carl Sagan is generally regarded as the father of modern probe theory. In his award-winning PBS television series Comos, first broadcast in 1980, Sagan famously said, "It is the height of arrogance to believe that extraterrestrials only use anal probes for research on humans and not all animal species."

For over a decade, Sagan's assertion that extraterrestrials use anal probes to study all creatures on our planet went unchallenged by the scientific community, but another quip from a famous scientist changed the way the world viewed alien anal probes. Though probe theory isn't mentioned in Hawking's book A Brief History of Time, in the film version, produced in 1992, Hawking states, "It's absurd to think that extraterrestrials would use anal probes on all of the animal species they study."

With all of our advancements in probe theory, it's difficult now to understand how revolutionary Hawking's statement was in 1992. By that time, Sagan's suggestion that "It is the height of arrogance to believe that extraterrestrials only use anal probes for research on humans and not all animal species" was widely taught to school children and was his most often quoted saying. This author, along with many other young space enthusiasts who shopped at Spencer Gifts, even had a poster of Sagan and his saying on his bedroom wall in high school.

The popular press interpreted Hawking's statement as a shot at Sagan and ran stories about bad blood between the two. Many scientists, however, saw merit in Hawking's new line of thinking and quickly designed experiments to demonstrate the impracticality of using probes on all animals. A team of researchers at Stanford University studied the size variation of all the known animal anuses on Earth and estimated an extraterrestrial would need a whopping 4,000 different sized probes to explore them all effectively. Other scientists picked away at the edges, arguing that certain species were too large or too small to be practically studied. A blue whale, for example, was considered far too big to be beamed onto a ship for study, not because of the theoretical strength of a ship's tractor beam, but because of the inefficiency of intergalactic travel in a ship with enough empty space to put a 29-meter whale.

As probe theory grew in popularity, the United States government funded over $60 million in research by the end of the century. Controversy arose as the work became less theoretical, and many animal rights groups argued it was cruel for zoos to leave animals out at night for possible abduction. A five-year, $3.1 million NIH-funded effort that failed to effectively insert a probe into a flea led to a barrage of jokes on late-night talk shows.

Funding started to dry up in the late 1990s as innovative probe theory research became rare, and in a post-9/11 world, the public consciousness dramatically shifted. Probe theory was essentially dead. Alien anal probes, darlings of the scientific community in the 1990s, were now considered a quaint relic of a simpler time. Even researchers who had built their careers in the field publicly wondered if there was anything left to say.

However, probe theory was only dormant, not dead, and it would be revived twelve years later by an unlikely information source: Twitter. Astrophysicist Neil deGrasse Tyson said in a series of tweets, "There is no scientific reason for anal probes to be used repeatedly over decades. Particularly for a civilization with the advanced technology to visit other planets. The only plausible explanation is sexual."

Everything we understood about probe theory was turned on its head. The possibility that extraterrestrials may use anal probes on only humans hadn't been seriously considered since the 1970s. Suddenly, the scientific community went from having all of the answers to having none of the answers. In many ways, the field was even more wide open than in the golden age of probe theory. If the anal probes are sexual in nature and extraterrestrials are attracted to humans, what else might they be attracted to? Monkeys? All animals? Greek statues?

Now, there is a sense in the scientific community that we are on the cusp of a breakthrough, but it will require new ideas to carry the field forward. One promising study seeks to review records from the world's space agencies to see if the many animals launched into space may have returned with overlooked signs of abduction and probing. However, an influx of proposals with dubious scientific merit shows signs of the cash grab of the late 1990s, such as one study that (if funded) would collide pairs of gerbils in the Large Hadron Collider.
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Simply educating the public about probe theory may be the ultimate solution. Victims of alien abductions inevitably ask the wrong questions once aboard the spaceship, like "Where am I?" or "What’re you going to do with that probe?” instead of practical questions, like “Are you attracted to monkeys?”

Of course, science often surprises us, and the next great leap forward in probe theory may come from an entirely unexpected source. However, I can confidently say that we’re closing in on the answers to some of our most probing questions.