The probability of alien UFOs has not really changed

Interest in alien visitation has spiked following the recent release of an Pentagon report on their experiences with what they call unidentified aerial phenomena (UAP), or what are commonly called unidentified flying objects (UFOs). Despite the new report, the basic probability math of alien visitation has not changed by any significant amount after the release of new grainy videos. Here is what I maintain is the best answer at this time, in three sentences:

  • The probability that there is some kind of life elsewhere in the universe is extremely high.
  • The probably of concurrent intelligent life elsewhere is much lower, but still high.
  • But the probability of recent alien visitation to the Earth is extremely low.

So, let’s parse that statement out.

What is a UFO?

The primary human fallacy with this term is that the “U” in UFO stands for “unidentified,” and yet most of us hear “alien.” When you see something “unidentified” in the sky, your mind may jump directly to “Ooh, an alien,” but without any other information, the number of natural and man-made alternatives for anything you see in the sky is so big that the laws of probability lean heavily in that direction from the start. “Unidentified” really means “something you don’t normally see, but don’t get freaked out.”

The probability of “Life 1”

The “simple explanation” to the evolution of life on Earth and other planets in other solar systems is a probabilistic one. In the heaving chemical cauldron that was “early Earth” starting between 3.5 and 4.5 billion years ago, many trillions of very “promiscuous” carbon atoms [1] combined chemically with other elements, particularly hydrogen, oxygen, nitrogen, and phosphorus, in increasingly complex ways. At least two of those chemical combinations (RNA and DNA) turned out to be “self-replicating,” or able to make copies of their own complex structures. But that replication is sometimes very slightly imperfect, allowing for differing adaptations to their environment, and thus differing probabilities for further replication. That is what I call “Life 1,” which is biochemical structures (compounds made up of carbon, tied to other elements), replicating in more and more complex ways for several billion years.

Because there are trillions of other solar systems in the universe that have also been “cooking” the same chemicals for up to 14 billion years, the odds that DNA or some other form of replicating chemical information has emerged someplace else in the universe has to approach 100%. Think of it as very tiny odds of winning a lottery, but with trillions of tickets sold. The Law of Large Numbers says to bet on that one.

Then, there is “Life 2”

Katie, bar the door! DNA started replicating, and in always-changing forms. And with it carrying more and more “environment adaptation information,” until it nearly filled the Earth with “living things.” Then, after some four billion years of this “replication with modification and selection” process, YOU eventually showed up, a “winner” in the lottery of life. [2]

At some long ago, but vaguely defined, point along the way to “You,” that biochemical life became sentient (or “self-aware,” an entire other topic), which is what I call “Life 2.” The probability of “Life 2” evolving given “Life 1” first occurring is several “orders of magnitude” (powers of ten) less than the “Life 1” probability. Indeed, most of that intervening four billion years between “Life 1” and today had zero life forms that would approach any arguable level of self-awareness. The literal probabilistic odds are that most planets in distant solar systems have not yet reached that point, and most will never reach it.

Our probability estimate for sentient life on other planets in other solar systems has thus dropped significantly, However, due again to the Law of Large Numbers, and the huge number of other solar systems out there, there is still a very high degree of likelihood that “Life 2” has developed elsewhere in the universe. We are not alone.

Time…time…time see what’s become of me…

Pardon the Paul Simon reference, however the entirety of mankind’s civilized existence on Earth is but a blip in those 14 billion years since the Big Bang. Our one hundred years of radio transmissions, even traveling at the speed of light (one of the few ways in which an alien civilization might find our needle in a near-infinite haystack), have not made it more than one-thousandth of the way across our own galaxy, and there are billions more galaxies out there. Even adding a few hundred thousand years of future human development (I wish I were more confident about that), we still would not have moved past the “blip” phase on the cosmological calendar. For any alien race to “catch us with our pants down” at this moment in time would be an incredibly lucky dart throw across billions of years of time.

This is where those odds switch sides from very likely to very unlikely. You would be hunting for lost keys buried in the sand of a beach, but you would have no idea which beach, or even if the beach is on Earth or Mars (where it is a long way to the water), or whether they were dropped yesterday or one billion years ago.

Beam me up, Scotty…

Add to that the 14-billion-year cosmological history on which that one visiting alien civilization may have, at one narrow range of time, developed an as-yet explainable method for moving sentient life forms across multiple light-years of space, too often looking like a 1950s flying saucer movie in fuzzy pictures, and moving counter to all human-known laws of physics.

The seemingly-mere four light-years of distance separating the nearest star system from Earth is, in reality, 25 trillion miles. Yes, I have read Stephen Hawking, but the cosmological mathematics of possible “worm holes” through which “entangled subatomic particles” could conceivably pass through vast spans of space time is an entirely different thing from passing sentient life forms and large Buck Rogers spaceships over that distance. Sometimes “science fiction” is mostly just “fiction” and wishful thinking. The human-known laws of physics have dropped our odds of that visiting flying saucer a whole lot more, down to the “Don’t bet on it” level of 0.000-just-add-lot-of-zeroes-here-0001.

The more probable and less glamorous alternatives

Military and other observations of seemingly very-high-speed travel by UAPs are very subject to a well-known “brain misfire” called the “parallax illusion” or “motion parallax.” This occurs when you misjudge the distance of a moving object relative to your own movement or relative to a distant stationary object. The object can then appear to be moving at a much higher rate of speed than seems reasonable, or even appear to be not moving when you think it should be.

I would often experience this effect while sitting in commuter train in Paddington Station in London while the train on the adjacent track was moving out. For a moment, you are not sure which train is moving, which can be unnerving. Or if your moving train passes another going the other way on a close parallel track, the illusion of the speed of the other train is exaggerated. You both might be going only fifty miles per hour, but if you don’t “feel” your own forward movement, the other train “feels like” it is going one hundred miles per hour from your point of perception.

Amateur spotting of objects in the night sky is especially subject to the parallax effect, as it is very difficult to accurately judge distance and motion for lights in the night sky. It could be a star that is ten thousand light years away, or a firefly just a few feet from your face. And it is no coincidence that these reports often come from pilots in high-speed aircraft out over the ocean, with few visual clues required for perspective. Fast-moving planes make the judging of parallax effects even more problematic. It is difficult to get the human mind wrapped around the fact that your visual system is itself moving at hundreds of miles per hour, and that fly headed forward in your airplane cabin is moving even faster than the plane is. Our minds have not evolved to do this sort of mental calculation.

A second explanation is provided by experts in the radar and optical systems used in military aircraft which are known to produce visual “artifacts,” especially when used in infrared mode, that might look like objects external to the airplane but are, in reality, just internal camera and light effects. Many of the popular UFO videos have not been direct sightings, rather are being viewed secondarily through various tracking systems. And as I have recently written, what we believe that we “see with our eyes” is in large part a construction of our brain, with lots of “missing parts” filled in, not always accurately.

While governments are normally in denial, new aerial technologies are always being tested by our government, and likely by others. No one of these explanations definitively rules out an alien visitation, but so far, it has been a wise bet to rely on the laws of physics and politics as we know them. Finally, despite nearly all adults in the civilized world carrying around a high-resolution video camera in their pockets, the best we still get are fuzzy images of unexplained visual phenomena.

I sound like a naysayer here, but the reason that most scientists have not gone bonkers over the Pentagon report is that it really provided little information that would “move the odds” more than one zero or two out of an existing dozen (or more) zeroes beyond the decimal point. I often cite Bayesian thinking on this blog, and this is another example. If the new information coming into the equation, as shown below, is very tiny as compared with the existing “prior probability,” then the new “posterior probability” needle has not significantly changed. Is your next vacation drive one thousand miles long or one thousand miles plus one block? More grainy photos from fallible electronic tracking instrumentation does not change my bet. They are the “extra block.” I do not lose any sleep over alien invasions.

Bayes Theorem

In sum, as is true in far too much of science journalism, most of the media play on that recent Pentagon story has been, to use a technical term, really crappy, and some scientists need to review their Bayesian math.


  1. Because its atomic structure, carbon “likes” to bond with many other elements, and it can do so in an innumerable quantity of ways and structures. The “promiscuity” of carbon is actually a commonly used term in biochemistry.
  2. I always like to throw in Biff Rose’s recitation of the Joseph Newman poem “Paradise Lost,” a humorous view of the evolution of life on Earth:

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2 thoughts on “The probability of alien UFOs has not really changed

  1. Peter R Robinson

    Good article. One vital factor when computing the probability of intelligent life arising is that it requires stable life-suppporting conditions to exist on a planet WITHOUT EXCEPTION FOR SOME FOUR BILLION YEARS.

    We have no idea how unlikely that is.

    “‘We Are Probably Alone’” by Peter Rodes Robinson
    SETI, the Fermi/Hart Paradox, and the Great Filter.

    1. @rklindgren Post author

      Very true, although the estimate for the number of stars in the universe has been steadily growing, with one estimate at 1 billion trillion. Even the Fermi Equation starts to break down at those numbers. However, all but a few billion are so far away that the question of whether they have “life” becomes irrelevant.

      As for interstellar travel, the HG Wells “War of the Worlds” scenario is still pretty relevant, where neither aliens not humans would survive infestation from infectious agents from another planet. I thought the intestinal bugs I acquired on my trip to Bolivia a few years ago would kill me.

      We assume that we humans are “individuals,” when we may just be the “domesticated animals” of our gut biome, which we carry with us wherever we go. Mess with those suckers the wrong way and you are dead.


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