A clash between U.S. President Donald Trump and former President Barack Obama has rekindled the debate over aliens. After former President Obama used the phrase "aliens are real" on a recent podcast, President Trump criticized him, saying he "leaked classified information." The political back-and-forth spread quickly, and online, suspicions that "the government might be hiding something" mixed with rebuttals that it is "merely scientifically plausible."
President Trump said he would begin the process of releasing government documents related to extraterrestrial life and unidentified anomalous phenomena (UAP). UAP is a broader official term than the older unidentified flying object (UFO), encompassing unidentified anomalies in the air, space, and undersea.
Separate from the political fight, the scientific community's position is relatively clear. On whether life exists somewhere in the universe, researchers are keeping the possibility open and continuing their work, and on whether extraterrestrial life has visited Earth, there is still no verified evidence—that is the conclusion.
◇ From hypothesis to statistics in the debate over extraterrestrial life
Until the 1990s, the existence of planets outside the solar system—exoplanets—was closer to a hypothesis. But now, 6,107 exoplanets have been confirmed according to the National Aeronautics and Space Administration (NASA) archive, and some are analyzed to lie in the "habitable zone," where liquid water could exist. As the number of planets has grown exponentially, the discussion that "intelligent life may have arisen somewhere" has shifted into a statistical question.
The so-called "Drake equation" represents this discussion. It is closer to a thought experiment estimating how many communicative civilizations might exist in our galaxy. It multiplies several variables, such as the number of stars, the fraction with planets, the probability of life arising, and the probability of evolving into intelligent life. Recently, researchers have been replacing observable factors like the number of stars and planets with actual data, attempting a probability-based discussion that is narrower than vague guesses.
In 2016, U.S. astronomers Adam Frank and W.T. Sullivan modified the Drake equation to calculate, based on exoplanet data, the probability that "no technological civilization other than humanity has ever existed in the entire history of the universe." They concluded that unless the chance of a technological civilization arising is extraordinarily low, the likelihood that humanity is unique in the universe's history diminishes.
There is caution as well. In 2020, Columbia University professor David Kipping noted that while life appeared relatively early on Earth, intelligent life like humans emerged much later. He analyzed this statistically and offered the interpretation that "life itself may be relatively common, but the evolution of intelligence may not be." Put simply, microorganisms may exist throughout the universe, but beings that have built civilizations like us could be rare.
Kipping added, however, "We can only present statistical probabilities based on what happened on Earth," and emphasized, "We must never give up on efforts to find intelligent life beyond Earth."
◇ "It seems likely, so why don't we see it?"… the Fermi paradox and the race to observe
The concept often cited here is the "Fermi paradox." Put simply, given the sheer number of stars and planets in the universe, multiple civilizations should plausibly exist—so why have we not clearly found traces of them? Rather than denying the existence of extraterrestrial civilizations, the paradox is closer to a concept that poses a scientific task: the need for more precise observations and more data.
In response, observation and exploration projects are in full swing. NASA has spent massive budgets over decades to search for life in space. Recently, it launched Europa Clipper to assess the habitability of Jupiter's moon Europa, and it is also pushing the Dragonfly mission, a rotorcraft lander to study the environment of Saturn's moon Titan. It is additionally developing the Habitable Worlds Observatory (HWO), a more powerful next-generation space telescope targeted for the 2030s.
Harvard University professor Avi Loeb is pursuing the Galileo Project, which aims to observe UAPs passing overhead using a network of small telescopes and instruments. In the search for extraterrestrial intelligence (SETI), a series of smaller projects continue to try to detect electromagnetic signals reaching Earth.
So far, however, none of the U.S. government's official reports or investigative findings has presented definitive evidence that an extraterrestrial civilization visited Earth. The All-domain Anomaly Resolution Office (AARO) at the U.S. Department of Defense and NASA's UAP expert panel have recorded numerous unidentified phenomena over the past decade or so, but have not concluded that they are extraterrestrial technology or life.
In a UAP-related FAQ, NASA said, "It is difficult to draw scientific conclusions due to a lack of high-quality observational data," and AARO says, "To date, we have found no evidence of verifiable extraterrestrial presence, activity, or technology."