The Silurian Hypothesis is a thought experiment, a sort of scientific or philosophical game that graduate students play—similar to the Ship of Theseus, Schrödinger’s cat, or any one of Zeno’s paradoxes (Zeno of Elea: 490 BC–c. 430 BC). It was the subject of an academic paper published in 2018 by astrophysicists Adam Frank (1962– ) and climatologist Gavin Schmidt (date of birth not published). The purpose of this purely intellectual exercise was to understand what evidence of a civilization if any might remain a million years or more after its demise.
To apply this thought experiment to real life, one might consider the planet Mars. Once we reach the point where we can say there appears to be no indigenous life (microscopic or otherwise) on Mars, how might we surmise whether life ever existed in the deep Martian past? Incidentally, geological time on Mars is measured in Ga (giga-annum), or one billion-year increments.
“Who” came up with the Silurians?
The Silurian Hypothesis has nothing to do with the Silurian period on Earth; rather, it references several television shows in the Doctor Who series. In this popular British program, the Silurians are intelligent, technologically advanced reptiles with human-like attributes. They ruled on Earth before humans arrived but were driven underground into a state of timeless hibernation, to be awakened someday. Like, now.
One of the theories that accounts for unidentified anomalous phenomena (UAPs) is based, more or less loosely, on a scenario like this, though it does not require reptilians in particular. In this case, what clues might remain of this early civilization on the surface of this planet 414 million years later, after countless earthquakes, volcanic eruptions, floods, etc.?
It is important to note that there is absolutely no scientific or archaeological evidence to support these episodes involving Doctor Who!
The Silurian Hypothesis forms a methodological approach to evaluating not so much whether there is intelligent life on a planet at present, but whether there ever was. This approach could also be useful in examining comets, asteroids, and meteorites, which are thought to be devoid of organic molecules, proteins, amino acids, and so on. However, because they may have broken off from a planet in the distant past that did have life, they may possess clues and residual organic material.
Sentience
There are three general criteria for deciding whether a lifeform, no matter how simple or complex, is sentient. The fundamental questions are whether it is capable of self-awareness, perception, and the ability to experience sensations and emotions. But as you might infer, there are caveats. For example, a common earthworm might recoil from an electrical shock. But does this mean that annelids are intelligent? My golden retriever is self-aware, as far as I’m concerned. She recognizes, in particular, other dogs of her breed. When I am shaving in the bathroom, out of sight of my golden, she can see my reflection in the mirror and respond to my eye contact and gestures, even though she understands that the reflection she sees is not really me but a facsimile. She displays at least half a dozen emotions as well. Also, most dogs can choose a two-dimensional photo of their owner from an array of photos of other people unknown to them. Some of her behavior is simple conditioning (reward vs. punishment), but this is also how men learn what works when they want to put their wives in a romantic mood. They understand the rewards of candles over dinner, soft music, flowers, and what the consequences are if they don’t go the extra mile.
So, supposing my dog is sentient, how, then, is she intelligent? For one, she learns from experience. If, as a puppy, she saw a rabbit in the backyard, she would run to where the rabbit was, chasing it vainly across the lawn. Soon, she understood that in order to catch it, she should run to a point where the rabbit was not, in order to intercept the creature once it arrived. That tangent made the difference between failure and success. She can also play—and enjoys—a variation of the shell game (i.e., under which cup is the object?) Rather than repeat a wrong guess, she tries as many cups sequentially as she needs to in order to discover the object, and many times she finds it on the first attempt. If the object is under cup #2, she does not choose cup #2 more than once.
Yet, even though it is startling or endearing to see an animal display human-like traits, it is not frightening or incomprehensible. Who knows how some creature on another planet might display love and affection? The praying mantis kills its partner after mating. Is that preferable to earthly customs among humans?
Non-human intelligence
This term need not be scary. Some think of the supernatural or invaders from Mars. In fact, NHI is all around us and we embrace it. We find it in our pets, we use it in our cars and to look up information on our phones. When we fly, we surrender our very lives to the sophisticated controls and algorithms on the flight deck.
The term “non-human intelligence” (NHI) has been used to categorize several different concepts over the past two decades. It is sometimes used to refer to machine learning. Examples of machine learning include facial recognition systems, chatbots, and translation services. Chatbots have been heavily involved in customer service and technical support, among other areas. In the field of robotics, NHI can also refer to the programming that allows for fine object manipulation and repetitive motions. Robotics have been assisting auto manufacturers for decades, accomplishing tedious or dangerous tasks. Neural networks enable radiologists to obtain a second opinion on their interpretations of X-rays and scans, sometimes comparing a patient’s images to those of thousands of other patients. Additionally, people with hearing impairments can have verbal instructions or speeches converted to text as a matter of convenience or necessity.
Non-human intelligence exists in our natural world, again with our pets for example. And beyond that there are dolphins, corvids, primates, insects such as bees and so on.
In the context of Unidentified Anomalous Phenomena, NHI refers to extraterrestrial, interdimensional or other life forms, particularly in terms of their intentions, capabilities, technological accomplishments, and so on.
A good definition of the term non-human intelligences come from Senate Amendment 2610 to the National Defense Authorization Act of 2025 (Sect_03(13) of the 118 Congress which unfortunately was not ultimately passed into law.1 Still, however, it demonstrates the interest the Congress has in this area. SB 2610 defined NHI as:
. . . sentient intelligent non-human lifeform regardless of nature or ultimate origin that may be presumed responsible for unidentified anomalous phenomena or of which the Federal Government has become aware.
We hope that inhabitants in the surrounding planetary systems have good manners as well as some basic sense of morality, though we know that some will likely not. But what if an apex predator from another planet does not possess a soul? What if his race arrives on earth for the purpose of plundering it for its resourcesor becuse they need a home and their plan is to liquidate us (perhaps in the literal sense of the word)? Stories like this are what give credence to the Dark Forest hypothesis.
Obviously, the definition can deal with the outcomes and designs of Artificial Intelligence, but notice the words “ultimate origins” in the amendment. What does that mean? Russia? Pluto? Comet 3I/ATLAS? The fifth dimension?
And, non-human intelligence exists in our natural world. Witness dolphins, corvids, primates, insects such as bees and so on. Then there is artificial intelligence, which is growing by leaps and bounds. In some ways it may surpass human intelligence while in other ways it may never quite be capable of how we reason and behave. Increasingly people in our society, particularly youth use AI to create friends or lovers, though this does not portend well for the future of interpersonal relationships.
We hope that people around us have some basic sense of morality, though we know that some do not. But what if an apex predator from another planet does not possess a soul? What if his race arrives on earth? Stories like this are what give credence to the Dark Forest hypothesis.
How might truly alien life communicate with us? Aloud in our own language (or theirs)? Symbolically as Amy Adams did in the 2016 film Arrival? What if they communicated telepathically? What if there were able to exert some control over our own minds?
Ultraterrestrials/Cryptoterrestrials
The ongoing debate about UAPs and NHIs is driven by anomalous observations and evolving definitions, with NHI serving as a flexible term that encompasses a range of speculative yet scientifically open possibilities.
Non-human intelligence (NHI) need not be extraterrestrial in origin; indeed, the origins of UAPs might be more conveniently located on Earth. For example, they might be ultraterrestrial. An ultraterrestrial is a hypothetical, highly advanced entity or civilization that originates from Earth or another dimension but is not from another planet within our universe. This entity is sometimes referred to as a cryptoterrestrial. These creatures could be pre-Diluvial, meaning they existed either before the Great Flood or even prior to the creation account of Genesis 1:1-2.2
Navy F-18 pilot Ryan Graves who testified to Congress in July 2023 described a UAP that he sighted at a distance as close as 50 feet from his aircraft. According to Lt. Graves, he observed a “dark gray or a black cube inside of a clear sphere.” He estimated the diameter of the sphere to be 5 to 15 feet. Note that there are no external control surfaces such as wings, indications of propulsion such as vents, and yet this object can outperform our most advanced aircraft.
Footnotes
1The amendment (SA 2610) was defeated largely through the efforts of one man, Senator Roger Wicker of Mississippi, who, at this very moment, is trying to keep any similar amendment to the Defense Authorization Act from being added in the coming weeks ahead. This reportedly would be the third time he has done so. His second largest campaign contributor is Lockheed Martin, a defense company that is frequently named by UAP Whistleblowers as being interested in UAP crash recoveries, reverse engineering and so on.
2There are significant references in Jewish commentaries—and a few scattered hints in Christian and apocryphal thought—that support the possibility of a civilization or cycles of existence before the creation described in Genesis 1. For example, in the Babylonian Talmud, Tractate Sanhedrin 38b, Rabbi Meir (c. 70 AD – c. 140 AD) said: “There were 974 generations created before Adam. Each generation was destined to be created, but they were not created because they were not deemed worthy.” Just where Rabbi Meir ben Baal HaNess got this number and this information is not given, and it may be sheer nonsense or at best irrelevant and obscure.
The early church fathers were not particularly supportive of any pre-existence before Adam though the Gnostics were.
Genesis 1:2 describes the earth as “formless and void” (tohu va-bohu), with darkness on the face of the deep, which some have interpreted as evidence of a previous order that was destroyed, the so-called “Gap Theory”. This gap would conveniently provide a niche for dinosaurs and other prehistoric life.
Also, Isaiah 45:18 is sometimes cited using the same adjective: “He did not create it a waste (tohu), He formed it to be inhabited,” suggesting that an inhabited world existed before the chaotic state in Genesis 1:2.
Additionally, it is possible that some society has mastered advanced technology dealing with optical illusions and created a cloaking apparatus that relieved them of the responsibility and challenge of constructing a kingdom on the ocean floor or several miles below the surface of the Earth. Their cities would exist in plain view, assuming we could actually see them.
This CTH speculation would, in the past, never have been approved by a thesis advisor for study. But then again, if we are on the threshold of some exotic revelation about UAPs, it is worth at least laying down the bare bones of a theory on which to build.
There is something called the crypto-terrestrial hypothesis (CTH), a fanciful theory that never gained much traction among serious scientists until the topic of UAPs finally became salient. Now more than ever it is acceptable to entertain scholastic research on UAPs which then raises addition questions such as where do they come from. If the beings that construct and operate the UAPs do not originate in a distant part of the galaxy, could they be living on earth, right under our noses? To that question, the answer is a very qualified “perhaps.” In that case, what scenarios are there? Altogether, there are four possible answers with varying degrees of plausibility:
- A hidden civilization of homo sapiens that has in the far distant past opted to conceal itself from others on the planet’s surface, either under the oceans, in deep caves or caverns, within thick jungles or other inaccessible terrain. This civilization as not only kept pace with the technological achievements of those on the surface, but as actually out-paced them (ergo, the UAPs).
- Another evolutionary branch that developed hominoid (though not human) creatures of compatible intelligence to us. This would be a hidden civilization as well.
- Time travelers from the future could almost as easily account for UAPs.
- Finally, these could be a realm similar to C.S. Lewis’s Narnia inhabited by denizens mentioned in our mythology. Such trolls, fauns, mermaids, dragons etc. would have somehow occasionally crossed the boundaries between our realm and theirs and became trapped here.
It is possible that some society has mastered advanced technology dealing with optical illusions and created a cloaking apparatus that relieved them of the responsibility and challenge of constructing a kingdom on the ocean floor or several miles below the surface of the Earth. Their cities would exist in plain view if we could actually see them. This CTH speculation would, in the past, never have been approved by a thesis advisor for study. Then again, if we are on the threshold of some exotic revelation about UAPs, it is worth laying down the basis of a theory on which to build.
Navy F-18 pilot Ryan Graves who testified to Congress in July 2023 described a UAP that he sighted at a distance as close as 50 feet from his aircraft. According to Lt. Graves, he observed a “dark gray or a black cube inside of a clear sphere.” He estimated the diameter of the sphere to be 5 to 15 feet. Note that there are no external control surfaces such as wings, indications of propulsion such as vents, and yet this object can outperform our most advanced aircraft.
Footnotes
1The amendment (SA 2610) was defeated largely through the efforts of one man, Senator Roger Wicker of Mississippi, who, at this very moment, is trying to keep any similar amendment to the Defense Authorization Act from being added in the coming weeks ahead. This reportedly would be the third time he has done so. His second largest campaign contributor is Lockheed Martin, a defense company that is frequently named by UAP Whistleblowers as being interested in UAP crash recoveries, reverse engineering and so on.
2There are significant references in Jewish commentaries—and a few scattered hints in Christian and apocryphal thought—that support the possibility of a civilization or cycles of existence before the creation described in Genesis 1. For example, in the Babylonian Talmud, Tractate Sanhedrin 38b, Rabbi Meir (c. 70 AD – c. 140 AD) said: “There were 974 generations created before Adam. Each generation was destined to be created, but they were not created because they were not deemed worthy.” Just where Rabbi Meir ben Baal HaNess got this number and this information is not given, and it may be sheer nonsense or at best irrelevant and obscure.
The early church fathers were not particularly supportive of any pre-existence before Adam though the Gnostics were.
Genesis 1:2 describes the earth as “formless and void” (tohu va-bohu), with darkness on the face of the deep, which some have interpreted as evidence of a previous order that was destroyed, the so-called “Gap Theory”. This gap would conveniently provide a niche for dinosaurs and other prehistoric life.
Also, Isaiah 45:18 is sometimes cited using the same adjective: “He did not create it a waste (tohu), He formed it to be inhabited,” suggesting that an inhabited world existed before the chaotic state in Genesis 1:2.
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