Human intelligence: have we reached the limit of knowledge?

Written by Maarten Boudry

Human intelligence: have we reached the limit of knowledge?
Credit: Mike Ver Sprill/Shutterstock

Despite huge advances in science over the past century, our understanding of nature is still far from complete. Not only have scientists failed to find the Holy Grail of physics—unifying the very large (general relativity) with the very small (quantum mechanics) – they still don’t know what the vast majority of the universe is made up of.

The sought after Theory of Everything continues to elude us. And there are other outstanding puzzles, too, such as how consciousness arises from mere matter.

Will science ever be able to provide all the answers? Human brains are the product of blind and unguided evolution. They were designed to solve practical problems impinging on our survival and reproduction, not to unravel the fabric of the universe. This realisation has led some philosophers to embrace a curious form of pessimism, arguing there are bound to be things we will never understand. Human science will therefore one day hit a hard limit—and may already have done so.

Some questions may be doomed to remain what the American linguist and philosopher Noam Chomsky called “mysteries”. If you think that humans alone have unlimited cognitive powers—setting us apart from all other animals—you have not fully digested Darwin’s insight that Homo Sapiens is very much part of the natural world.

But does this argument really hold up? Consider that  did not evolve to discover their own origins either. And yet somehow we managed to do just that. Perhaps the pessimists are missing something.

Mysterian arguments

“Mysterian” thinkers give a prominent role to biological arguments and analogies. In his 1983 landmark book The Modularity of Mind, the late philosopher Jerry Fodor claimed that there are bound to be “thoughts that we are unequipped to think”.

Similarly, the philosopher Colin McGinn has argued in a series of books and articles that all minds suffer from “cognitive closure” with respect to certain problems. Just as dogs or cats will never understand prime numbers, human brains must be closed off from some of the world’s wonders. McGinn suspects that the reason why philosophical conundrums such as the mind/body problem—how physical processes in our brain give rise to consciousness—prove to be intractable is that their true solutions are simply inaccessible to the human mind.

If McGinn is right that our brains are simply not equipped to solve certain problems, there is no point in even trying, as they will continue to baffle and bewilder us. McGinn himself is convinced that there is, in fact, a perfectly natural solution to the mind–body problem, but that human brains will never find it.

Even the psychologist Steven Pinker, someone who is often accused of scientific hubris himself, is sympathetic to the argument of the mysterians. If our ancestors had no need to understand the wider cosmos in order to spread their genes, he argues, why would natural selection have given us the brainpower to do so?

Mind-boggling theories

Mysterians typically present the question of cognitive limits in stark, black-or-white terms: either we can solve a problem, or it will forever defy us. Either we have cognitive access or we suffer from closure. At some point, human inquiry will suddenly slam into a metaphorical brick wall, after which we will be forever condemned to stare in blank incomprehension.

Another possibility, however, which mysterians often overlook, is one of slowly diminishing returns. Reaching the limits of inquiry might feel less like hitting a wall than getting bogged down in a quagmire. We keep slowing down, even as we exert more and more effort, and yet there is no discrete point beyond which any further progress at all becomes impossible.

There is another ambiguity in the thesis of the mysterians, which my colleague Michael Vlerick and I have pointed out in an academic paper. Are the mysterians claiming that we will never find the true scientific theory of some aspect of reality, or alternatively, that we may well find this theory but will never truly comprehend it?

In the science fiction series The Hitchhiker’s Guide to The Galaxy, an alien civilisation builds a massive supercomputer to calculate the Answer to the Ultimate Question of Life, the Universe and Everything. When the computer finally announces that the answer is “42”, no one has a clue what this means (in fact, they go on to construct an even bigger supercomputer to figure out precisely this).

Is a question still a “mystery” if you have arrived at the correct answer, but you have no idea what it means or cannot wrap your head around it? Mysterians often conflate those two possibilities.

In some places, McGinn suggests that the mind–body problem is inaccessible to human science, presumably meaning that we will never find the true scientific theory describing the mind–body nexus. At other moments, however, he writes that the problem will always remain “numbingly difficult to make sense of” for human beings, and that “the head spins in theoretical disarray” when we try to think about it.

This suggests that we may well arrive at the true scientific theory, but it will have a 42-like quality to it. But then again, some people would argue that this is already true of a theory like . Even the quantum physicist Richard Feynman admitted, “I think I can safely say that nobody understands quantum mechanics.”

Would the mysterians say that we humans are “cognitively closed” to the quantum world? According to quantum mechanics, particles can be in two places at once, or randomly pop out of empty space. While this is extremely hard to make sense of, quantum theory leads to incredibly accurate predictions. The phenomena of “quantum weirdness” have been confirmed by several experimental tests, and scientists are now also creating applications based on the theory.

Mysterians also tend to forget how mindboggling some earlier scientific theories and concepts were when initially proposed. Nothing in our cognitive make-up prepared us for relativity theory, evolutionary biology or heliocentrism.

As the philosopher Robert McCauley writes: “When first advanced, the suggestions that the Earth moves, that microscopic organisms can kill human beings, and that solid objects are mostly empty space were no less contrary to intuition and common sense than the most counterintuitive consequences of quantum mechanics have proved for us in the twentieth century.” McCauley’s astute observation provides reason for optimism, not pessimism.

Mind extensions

But can our puny brains really answer all conceivable questions and understand all problems? This depends on whether we are talking about bare, unaided brains or not. There’s a lot of things you can’t do with your naked brain. But Homo Sapiens is a tool-making species, and this includes a range of cognitive tools.

For example, our unaided sense organs cannot detect UV-light, ultrasound waves, X-rays or gravitational waves. But if you’re equipped with some fancy technology you can detect all those things. To overcome our perceptual limitations, scientists have developed a suite of tools and techniques: microscopes, X-ray film, Geiger counters, radio satellites detectors and so forth.

All these devices extend the reach of our minds by “translating” physical processes into some format that our sense organs can digest. So are we perceptually “closed” to UV light? In one sense, yes. But not if you take into account all our technological equipment and measuring devices.

In a similar way, we use physical objects (such as paper and pencil) to vastly increase the memory capacity of our naked brains. According to the British philosopher Andy Clark, our minds quite literally extend beyond our skins and skulls, in the form of notebooks, computers screens, maps and file drawers.

Mathematics is another fantastic mind-extension technology, which enables us to represent concepts that we couldn’t think of with our bare brains. For instance, no scientist could hope to form a mental representation of all the complex interlocking processes that make up our climate system. That’s exactly why we have constructed mathematical models and computers to do the heavy lifting for us.

Cumulative knowledge

Most importantly, we can extend our own minds to those of our fellow human beings. What makes our species unique is that we are capable of culture, in particular cumulative cultural knowledge. A population of human brains is much smarter than any individual brain in isolation.

Human intelligence: have we reached the limit of knowledge?
Are we cognitively closed to cosmology? Credit: Mohamed Ali Elmeshad/Shutterstock

And the collaborative enterprise par excellence is science. It goes without saying that no single scientist would be capable of unravelling the mysteries of the cosmos on her own. But collectively, they do. As Isaac Newton wrote, he could see further by “standing on the shoulders of giants”. By collaborating with their peers, scientists can extend the scope of their understanding, achieving much more than any of them would be capable of individually.

Today, fewer and fewer people understand what is going on at the cutting edge of theoretical physics—even physicists. The unification of quantum mechanics and relativity theory will undoubtedly be exceptionally daunting, or else scientists would have nailed it long ago already.

The same is true for our understanding of how the human brain gives rise to consciousness, meaning and intentionality. But is there any good reason to suppose that these problems will forever remain out of reach? Or that our sense of bafflement when thinking of them will never diminish?

In a public debate I moderated a few years ago, the philosopher Daniel Dennett pointed out a very simple objection to the mysterians’ analogies with the minds of other animals: other animals cannot even understand the questions. Not only will a dog never figure out if there’s a largest prime, but it will never even understand the question. By contrast, human beings can pose questions to each other and to themselves, reflect on these questions, and in doing so come up with ever better and more refined versions.

Mysterians are inviting us to imagine the existence of a class of questions that are themselves perfectly comprehensible to humans, but the answers to which will forever remain out of reach. Is this notion really plausible (or even coherent)?

Alien anthropologists

To see how these arguments come together, let’s do a thought experiment. Imagine that some extraterrestrial “anthropologists” had visited our planet around 40,000 years ago to prepare a scientific report about the cognitive potential of our species. Would this strange, naked ape ever find out about the structure of its solar system, the curvature of space-time or even its own evolutionary origins?

At that moment in time, when our ancestors were living in small bands of hunter-gatherers, such an outcome may have seemed quite unlikely. Although humans possessed quite extensive knowledge about the animals and plants in their immediate environment, and knew enough about the physics of everyday objects to know their way around and come up with some clever tools, there was nothing resembling scientific activity.

There was no writing, no mathematics, no artificial devices for extending the range of our sense organs. As a consequence, almost all of the beliefs held by these people about the broader structure of the world were completely wrong. Human beings didn’t have a clue about the true causes of natural disaster, disease, heavenly bodies, the turn of the seasons or almost any other natural phenomenon.

Our extraterrestrial anthropologist might have reported the following: “Evolution has equipped this upright, walking ape with primitive sense organs to pick up some information that is locally relevant to them, such as vibrations in the air (caused by nearby objects and persons) and electromagnetic waves within the 400-700 nanometer range, as well as certain larger molecules dispersed in their atmosphere.

“However, these creatures are completely oblivious to anything that falls outside their narrow perceptual range. Moreover, they can’t even see most of the single-cell life forms in their own environment, because these are simply too small for their eyes to detect. Likewise, their brains have evolved to think about the behaviour of medium-sized objects (mostly solid) under conditions of low gravity.

“None of these earthlings has ever escaped the gravitational field of their planet to experience weightlessness, or been artificially accelerated so as to experience stronger gravitational forces. They can’t even conceive of space-time curvature, since evolution has hard-wired zero-curvature geometry of space into their puny brains.

“In conclusion, we’re sorry to report that most of the cosmos is simply beyond their ken.”

But those extraterrestrials would have been dead wrong. Biologically, we are no different than we were 40,000 years ago, but now we know about bacteria and viruses, DNA and molecules, supernovas and black holes, the full range of the electromagnetic spectrum and a wide array of other strange things.

We also know about non-Euclidean geometry and space-time curvature, courtesy of Einstein’s general theory of relativity. Our minds have “reached out” to objects millions of light years away from our planet, and also to extremely tiny objects far below the perceptual limits of our sense organs. By using various tricks and tools, humans have vastly extended their grasp on the world.

The verdict: biology is not destiny

The thought experiment above should be a counsel against pessimism about human knowledge. Who knows what other mind-extending devices we will hit upon to overcome our biological limitations? Biology is not destiny. If you look at what we have already accomplished in the span of a few centuries, any rash pronouncements about cognitive closure seem highly premature.

Mysterians often pay lip service to the values of “humility” and “modesty”, but on closer examination, their position is far less restrained than it appears. Take McGinn’s confident pronouncement that the mind–body problem is “an ultimate mystery” that we will “never unravel”. In making such a claim, McGinn assumes knowledge of three things: the nature of the mind–body problem itself, the structure of the , and the reason why never the twain shall meet. But McGinn offers only a superficial overview of the science of human cognition, and pays little or no attention to the various devices for mind extension.

I think it’s time to turn the tables on the mysterians. If you claim that some problem will forever elude human understanding, you have to show in some detail why no possible combination of mind extension devices will bring us any closer to a solution. That is a taller order than most mysterians have acknowledged.

Moreover, by spelling out exactly why some problems will remain mysterious, mysterians risk being hoisted by their own petard. As Dennett wrote in his latest book: “As soon as you frame a question that you claim we will never be able to answer, you set in motion the very process that might well prove you wrong: you raise a topic of investigation.”

In one of his infamous memorandum notes on Iraq, former US secretary of defense, Donald Rumsfeld, makes a distinction between two forms of ignorance: the “known unknowns” and “unknown unknowns”. In the first category belong the things that we know we don’t know. We can frame the right questions, but we haven’t found the answers yet. And then there are the things that “we don’t know we don’t know”. For these unknown unknowns, we can’t even frame the questions yet.

It is quite true that we can never rule out the possibility that there are such unknown unknowns, and that some of them will forever remain unknown, because for some (unknown) reason human intelligence is not up to the task.

But the important thing to note about these unknown unknowns is that nothing can be said about them. To presume from the outset that some unknown unknowns will always remain unknown, as mysterians do, is not modesty—it’s arrogance.


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Comments (12)

  • Avatar

    Joseph Olson


    Sadly, many never progress beyond primary school learning. Many have curiosity thwarted by secondary school. The 5% who progress to college are suffocate by politically correct dogma, leaving only 0.5% of the population even capable of grasping the ‘limits of knowledge’ hypothesis. Of those, most are compartmentalized and are only capable of understanding in their narrow scope. Short a Nouveau Renaissance, we have passed the arc of general human knowledge.

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    Vance Lunn


    I do not know if many who come here simply perusing great science articles will understand what a truly dangerous line of thinking this is. If the dominant message in schools, media, and grom governments became “There is an upper limit to what we can learn and we have already reached that limit.”, then people would stop trying to learn and to innovate. Oppressive power hungry regimes would love to oppress the acquisition of knowledge in this soft, subtle way.

    We don’t even use more than 10 percent of our brain capacity. True, there is a limit to how fast our brains cam process data and thus come up with solutions, but we have already built machines that can far exceed this limit, just like we have built machines to help us fly when we lack the equipment naturally to do so. I certainly hope this idea never takes hold. There would be few greater tools of oppression than the teaching of such a paradigm.

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      I disagree .. just because I can’t know everything doesn’t hold me back from trying to learn everything that I can. And as far as innovation .. forget it .. we have not slowed in innovation whatsoever .. moreover, we currently innovate at a faster rate than we ever have before. And as long as there is a perceived “need”, we will continue to innovate without any perceivable end.

      There may be a limit to our knowledge, and I believe realistically there is, but I don’t see how that would preclude us from attempting to attain a virtually limitless list of aspirations.

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      So, there is a limit to how good I can play golf. A hard limit. I can never do better than a hole-in-one on every hole. However, that doesn’t stop me from trying!!! .. and I think the very same could be said for general knowledge and innovation as well.

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    Jim Beichler


    I greatly enjoy your online articles, both as a professional scientist (theoretical physicist) and a historian of science. In some cases, you seem to be .the only honest scientific publication about some of the important issues we face in the world today. I often put references to your work on Facebook, so others can learn the truth about some of the scientific issues that have been falsely co-opted by politicians and political pundits instead of listening to what the politicians (falsely) tell us (lie about) that science says to support their own political agendas. Hope you don’t mind the publicity and extra advertising. If you ever want some good topics, ideas and/or or articles, I would be willing to contribute or talk to some of your reporters on the important scientific issues of the day.

  • Avatar

    Andy Rowlands


    Some very interesting ideas here, though I don’t neccessarily agree with them. My own personal belief is the human mind has an almost limitless capacity to absorb information, but with time our memory fails and we start to lose some of that information. I think there is much more about the universe we don’t know, even with the vast amount of information we have gleaned about it. I also think machines like the LHC will delve more and more deeply into the sub-atomic world, at least until we run out of money to build them any bigger. When Peter Higgs theorised the particle now named after him back in 1964, he never thought he’d actually see it, but he was there at Cern when they found it.

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    The Hitchhiker’s Guide to The Galaxy, was a brilliant spoof of astronomy, aliens and of course the (false) big bang theory.Douglas Adams was a genius writer.

    No they wont marry Quantum physics and General Relativity. The 2 are probably incompatible at current levels. What goes on at 10 ^ -15m controls what goes on at 10^15m! That says that nuclear physics controls what the galaxies do.

    Suggested reading find, Hoyle (greatest astrophysicist) Burbidge and Narlikar Quasi Steady State cosmology, search in

    Im not sure if we, humans, have reached any limit, whats more probable is there is just information overload, there is so much data, due to technology esp. satellite data, that is is overwhelming researchers who have to produce the goods in limited time. They havent the time to really ‘think’ about the problems. Most of the astro data is proving the BB theory wrong, but because it is entrenched, it cannot be questioned. At the early 20th century when the great physicists were around they had more time. I heard Fred Hoyle say that in that he hadnt time to really think, he was too busy for many years.

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    So we have a limit to our knowledge, or is it we have a limit on our understanding of it?
    Sure some humans can be very specialized in one field or another in certain aspects of study but are there not individuals who are very adapt in most fields they attempt?
    Overall I believe that it is the sum total of human knowledge that will continue to advance (in our faulty error prone way), however it is in understanding the totally of all knowledge where we come unglued, and have to rely on a few people who can stretch their imagination to see the majority of it. Hopefully such people have good communication skills or the message will be lost even for the brightest among us.
    Basically we have 3 discrete limits to intelligence —
    Knowledge, understanding, and imagination, and they work in concert. When all three are well balanced true knowledge and understanding can be found.

    Simple question for the more adept here —
    Is the passage of time a constant or a variable? (Provide incontrovertible and verifiable observational evidence for your answer. )

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      Herb Rose


      Hi Tom,
      The answer is that the passage of time is variable according to the observer. For some insects a day is a lifetime while for some trees it is but a moment in their lives. The reality is that there is no time only energy. We use the energy of different objects (the orbiting of the Earth around the sun, the rotational energy of the Earth, the orbital energy of the moon) to create units of time so we can communicate with others with a common reference frame. You cannot separate time out of V^2 anymore than you can determine the weight of a bolt by the torque used to affix it to an object. There is no past or future only the present and the only constant is change. The rate of change or time varies for everything and while things may have similar rates of change they are different. We all live a lifetime but that lifetime is different for everyone. Time is just a measuring unit like a kilogram, meter, calorie, or liter that are artificial creations allowing for more accurate communications.

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        Yes indeed Herb Rose,
        However my point is that if the passage of time is a variable — that is to say all of us at this instant within our bubble of reality, and all physical constants within it, change to accommodate that change in time’s rate — then we would not know that anything was different. Of course that means it does not make any difference to us locally, things would still be as they are.
        The upshot is though, we have no definite method of knowing that time’s rate of change across the universe (or between galaxies) is progressing at the same rate as we do as we exist within the universe, therefore can not readily tell. We are like a fish staring through a transparent medium unable to tell whether distant objects are truly near or distant because we can not see that the medium itself (time) varies.
        Maybe those so called ‘blackholes’ are just regions where time progresses at such incredibly slow rates that they can not be accurately observed.

        I suppose it’s having a quote by Douglas Adams in the essay. I inevitably recall his flippant and serious line …

        “Time is an illusion. Lunchtime doubly so.”
        ― Douglas Adams, The Hitchhiker’s Guide to the Galaxy

        and that gets me thinking this way!

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          Herb Rose


          Hi Tom,
          You are questionings what is the proper reference point for making any measurement. If every object on Earth doubled in size we would not notice because all measurements are made from our perspective. The speed of light varies with the strength of the magnetic and electrical fields it travels in but if we say that the speed of light is constant than distance and time vary. If everything is variable then what do we establish as a basis to measure how things are varying?
          My opinion is that the proper reference point for measuring any characteristic of an object is the center of the energy field that organizes those objects.
          The Earth is a unit with its own energy field and objects in that field are measured from the reference point of the center of the Earth.
          The moon is another unit that has its own energy field and the position, speed, and other properties of objects on the moon are measured from the center of the moon not from the perspective of the Earth unit.
          The energy fields of the moon and Earth combine to form a larger unit that orbits the sun. The Earth and moon have no position or speed relative to the sun because their units are not in the organizing energy of the sun. It is the larger energy field formed from their combined fields that has position and velocity relative to the sun.
          The energy fields of atoms combine to form molecule units, which then combine to form larger objects with a larger energy field and the process continues through planets with moons, to solar systems, to galaxies, and galaxy clusters.
          It is energy that gives structure to all the objects in the universe and each unit has its own time frame and central reference point
          In atoms where electrons can disappear and reappear at a different position without moving how do you distinguish this disappearance and instantaneous reappearance from something traveling faster than the speed of light, or our speed of light?.

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      Hi Tom. Time is constant ’cause I said so. Anybody can ask me if they wish to verify it.

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