The Frontiers of Knowledge Cover

A. C. Grayling on What We Know—and Have Yet to Discover—About the Universe, Our Past, and the Mind

It’s remarkable to think that it was only a few centuries ago that the majority of the Western world believed that the earth was less than 10,000 years old, that the sun and planets revolved around the stationary earth, and that humans were specially created in God’s image, equipped with immortal souls that survived bodily death to inhabit, for all eternity, a supernatural realm (a subset of the population, amazingly enough, still believes all or most of this). 

Since then, our picture of the world has changed dramatically, to say the least. We now know that the universe is billions of years old, that the earth is one of an estimated 700 quintillion planets occupying one of around 100 billion galaxies in the observable universe, and that humans are one among a number of primate species having evolved over the course of millions of years. 

The incredible story of how we came to know all of this, what we have left to discover, and the lessons we’ve learned about the process of inquiry itself is the ambitious project undertaken by the philosopher and polymath A. C. Grayling in his latest book, Frontiers of Knowledge: What We Now Know About Science, History, and the Mind. Having already written The History of Philosophy in 2019 (one of, if not the best single-volume accounts of the history of the subject), Grayling turns his attention to the development and current state of our scientific and historical knowledge. 

Grayling sets out to explore three subjects that have utterly transformed our modern world-views: science, history, and psychology, and more specifically, fundamental physics and cosmology, human evolution and our pre-classical past, and the new sciences of the brain and mind, making up the three main sections of the book. 


Grayling begins part one by recounting the history of technology, the rise of science, and the development of modern physics. But this is not simply a book about the history of science. Grayling is more interested in the deeper epistemological questions concerning how we know what we do and what we’ve discovered about the process of scientific discovery itself. As Grayling wrote:

“[In addition to what we know], it also matters that we understand how we know. When we see how scientific and historical knowledge is acquired, what problems are overcome in acquiring it, and what questions are raised about the assumptions and methods involved, we not only learn how to evaluate what we know, but we also learn a great deal about responsible thinking and the demands of intellectual honesty. These matter in every sphere of human activity, and they are at a premium.”

If we really want to understand the state of knowledge in physics, for example, we can’t just set about learning the history of physics and its various experiments and discoveries. We must also   consider the methodological principles by which those discoveries were made, the philosophical implications of those discoveries, and the fundamental philosophical problems associated with their interpretations. This is, in fact, what is missing, or else covered inadequately, in most accounts of popular science written by practicing scientists. 

To take one example of a methodological problem (Grayling lists a dozen), consider the Ptolemy Problem. Here’s how Grayling describes it:

“Ptolemy’s geocentric [earth-centered] model of the universe ‘worked’ in a number of ways, permitting the successful navigation of the oceans and prediction of eclipses, thus showing that a theory can be efficacious in some respects while still being incorrect. How do we avoid being misled by pragmatic adequacy?”

This should bring to mind the current state of our knowledge in quantum physics; while quantum mechanics is pragmatically adequate—being responsible for a host of technologies—this fact in itself—just as with the geocentric model of the universe—is no guarantee that it is the correct model of reality. Basic methodological considerations such as these—often overlooked in the more superficial popular science books available—is what sets Grayling’s book apart from the others.

The most interesting part of Grayling’s coverage of particle physics is his suggestion that the reason quantum physics seems so foreign to us is that we are not cognitively primed to understand scales that small. He notes how contemporary cognitive science is catching up to the transcendental idealism of Immanuel Kant, which essentially states that how the world appears to us is a product of our cognitive capacities, not how the world is “in itself.” 

Any researcher studying human perception understands this. Taking vision as an example, think about how, as light enters the lens of the eye and strikes the retina, an electrical impulse is sent along the optic nerve to the visual cortex in the occipital lobe of the brain, where the image is “seen.” The resulting image, however, is only a re-construction by the brain of electricity and chemical reactions—encased as they are in our pitch-black skulls—into a three-dimensional full-color image that is projected “out there” in three-dimensional space.

The eyes, in this case, are not acting as “windows” into the world, where the brain just sees an unadulterated picture of reality; instead, the brain is actively creating our reality based on how it is designed to structure experience. We can never step outside of our brains to compare our perceptions to how the world “really is,” but there is no reason to suppose that our brains are primed to pick up on every aspect of the underlying reality, only the parts which impinge on our perceptual systems and then only based on how they are reconstructed in the “virtual reality” created by our cognitive architecture. (Keep in mind, for example, that visible light accounts for only 0.0035 percent of the entire electromagnetic spectrum.)

As Grayling notes, this is a big clue as to why quantum physics is so puzzling, and a point that escapes the notice of most philosophically-naive physicists. If what we are perceiving in the world of everyday objects is not the world in itself, but rather our own cognitive constructions—like the icons on a computer interface that mask the internal workings of the computer—then even if we use technology to penetrate smaller scales, we are still only able to conceptualize subatomic scales according to our macroscopic pictures of reality. And if our understanding begins to break down, it’s not because we have yet to fully understand the subatomic world, it’s because we don’t have the cognitive capacity to ever understand the subatomic world, or the fundamental structure of reality that exists at scales our brains never evolved to care about. 

To take the computer example a little further, if everyday objects are like the icons on a computer interface, then zooming in to everyday objects with the assistance of technology is like zooming in on the icons to discover that they are composed of pixels. But whether viewing the icons from a distance or up close as a collection of pixels, both perspectives still mask the underlying operations of the computer—the hardware, transistors, and electrical activity responsible for the generation of the icon images—in the same way that everyday objects and the subatomic world mask an underlying reality we’re not equipped to penetrate.  

As Grayling points out, the current mysteries of quantum physics can then be explained in one of two ways. The first option is to suppose that our theories of quantum physics are either wrong or incomplete, but their experimental success suggests otherwise (unless this is an example of the Ptolemy problem described above). The second possibility—and one I find to be more likely—is that, as Grayling puts it, “the cognitive architecture of our thought imposes conceptions of order, causality, linearity, consistency, monotonicity, uniformity, predictability, and so on, which are as useful to conceptualizing quantum phenomena as it would be to apply dog-grooming techniques to solving quadratic equations.” 

We simply did not evolve to understand the very small and very large scales of space and time that exist outside of our cognitive and experimental reach. This may sound like a defeatist position—and we may well do better to assume it’s not true, in case new discoveries or experiments prove it to be wrong—but it does go a long way in explaining our lack of progress in understanding the incoherence of the quantum world. 

This Kantian way of seeing the world also explains why mathematics is so effective in science; if we experience the world according to the way our brains structure reality—and our brains structure reality quantitatively in space and time—then it is no longer such a mystery as to why that particular tool or way of thinking is so effective. The corollary, however, is that, as we come to rely more on mathematics to explain the nature of reality, we must confront the possibility that what we’re describing has more to do with the nature of our minds than with nature itself. 

Grayling ends the section on science by considering whether or not we are justified in seeking a “theory of everything,” and why we are so obsessed with the idea that all of reality must necessarily be reduced to a single substance or equation. The origin of this idea lies with the ancient Greeks—and specifically Parmenides—but there is little reason to think that the universe out of necessity must conform to our ideas about how we think the universe “should” be. And even if experiment or mathematical discovery suggests that the universe is structured in a particular way, it’s possible that, as discussed above, this is telling us more about how our brains actively construct reality than reality itself. 

Kant, incredibly, was aware of all of this long ago. In the Critique of Pure Reason, Kant wrote:

“Human reason has the peculiar fate in one species of its cognitions that it is burdened with questions which it cannot dismiss, since they are given to it as problems by the nature of reason itself, but which it also cannot answer, since they transcend every capacity of human reason.”

If modern science is butting up against those cognitive limitations, the prospects of discovering a “theory of everything,” or explaining the deep mysteries of the quantum world, are slim. Still, we have no choice but to pursue the answers, due to innate human curiosity and because it cannot be predicted ahead of time what human ingenuity will discover. For this reason, cognitive closure—based on the human desire to eliminate ambiguity and arrive at definite conclusions—is one of the biggest intellectual mistakes we can make, and represents the most significant obstacle to continued progress. We must push forward, keeping in mind the limitations and issues we must overcome.  


Next, Grayling turns to history, as he recounts our evolutionary and pre-classical past, noting how it was not until as late as the nineteenth century before we were able to piece together anything at all (excluding mythology) about history prior to ancient Greece. Before then, most people just assumed that pre-history was what the Old Testament said it was. We now have a much richer conception of our past compared to the 6,000 years presented in the Bible, including the fact that we used to co-exist with several other species of Homo before they all went extinct. 

Sticking with the same approach, Grayling presents a clear picture of what we know about our past, how we know it, what we have left to learn, and the methodological considerations and debates that are often missing from historical accounts that paint a far more straightforward picture than what the evidence allows. 

The strength of this section lies in Grayling’s consideration of the philosophy of history, and the question of whether we can ever truly understand the past in objective terms without reading into the past our present concerns, viewpoints, perspectives, and biases. 

Since we can reconstruct the past only through preserved remains and written accounts—and since we know that written accounts are not always reliable—we have reason to suspect that the past may have been significantly different from what we can assemble from the available evidence.

Consider that even reports of traffic accidents, for example, vary by observer depending on the vagaries of memory, disposition, sympathy, and motivation. And if accounts can vary widely concerning an event that just recently transpired, imagine how greatly the problem is exacerbated the further one goes back in time. 

All history, in a sense, is therefore selection and interpretation, often written by the victors, as exemplified in the numerous “patriotic” retellings of US history that exclude the genocide and removal of an entire native population. It must be remembered that what is left out of any historical account can be equally (or more) important than what is included, as is the method by which the assemblage of facts is interpreted in light of the motivation of the author. 

But history is not a merely subjective endeavor, either. While the past is messy and often uncertain, the process of historical inquiry has developed methods by which reasonable positions can be ascertained. History denial (Grayling covers Holocaust denial in great detail), revisionism, and conspiratorial thinking can be weeded out by the same process of discovery and peer review available in the natural sciences. Events with several credible, consistent accounts that all converge on a specific interpretation can be taken as highly probable to have occurred as documented, whereas events with a limited number of more questionable accounts should be viewed with more suspicion. 

Although certainty is elusive in the historical domain (as in all others), historical knowledge does not require certainty, either. Historical viewpoints need only be well supported in view of the totality of available evidence, and we must guard against our tendencies for cognitive closure, prepared to update our beliefs in the light of new evidence. As Grayling wrote:

“History as enquiry lives, develops, changes, fluctuates in focus and meanings, and the best hope of grasping history as the past is to cleave to the evidence, be scrupulous in reasoning, dispassionate in judgement, and never tempted to start from conclusions with the intention of bending facts to fit them. In that direction lies the possibility of convergence on a best-supported understanding of the past.”

The Mind

In the final section, Grayling covers the new sciences of the brain and mind, charting the evolution of our understanding of the brain, the rise of neuroscience, and the perpetual mystery of consciousness. Cognitive closure is a particular hazard in this area, exemplified by the philosophers that—based on the reductionist findings of neuroscience—proclaim consciousness to be an illusion simply because it can’t be explained in reductionist terms.

Of course, if consciousness is an illusion, these philosophers never tell us who or what, exactly, is being deceived. It seems far more likely that what neuroscience is showing us is a series of correlations between brain states and mental activity, but is effectively silent on how subjective experience—what it’s like to feel pain or see the color red—arises from the electrochemical excitations of the brain. 

Clearly, there is a deeper mystery here. On the one hand, you have physical objects that occupy space and that are positioned in time (including the brain itself). On the other hand, you have thoughts, emotions, and ideas, which, while just as real, are immaterial in nature and do not take up physical space. The fundamental task is how to explain the coexistence of both physical and immaterial realities, not to deny the problem. 

Several potential explanations exist: Perhaps everything is ultimately composed of matter, as the materialists suppose, or everything is composed of mind, as the philosopher George Berkeley and others have proposed. Or rather, mind and matter might interact with each other, as the dualists maintain, or, instead, mind and matter might not interact with each other but are simply two sides of the same coin operating in parallel, as Spinoza claimed. 

The remarkable fact is that, even with all the advances of neuroscience, we’re no closer to resolving these disputes. That’s why, as Grayling wrote, “the great, and true, commonplace about consciousness is that it is simultaneously the most familiar and the most mysterious thing in the universe.” 

Understanding the richness of the philosophical debate is what makes it so irritating when a neuroscientist or philosopher comes along and pretends to have solved the problem, or states that the problem doesn’t exist, or that consciousness is an “illusion.” There is a deeper mystery here waiting to be solved, and whether neuroscience will one day solve it remains an open question. The other possibility is that, once again, we’ve hit the limits of our understanding, unable to step outside of our own consciousness to study it in objective terms. 

One of the more interesting points in this section is Grayling’s assertion that we cannot understand the mind without reference to the physical and social environments in which it develops. And so even if the reductionist account is true—and all mental phenomena reduce to fundamental physics—as a method of explanation, physics and neuroscience offer very limited insights into the human mind. One is far better off learning about human nature by reading literature, history, and philosophy (the humanities), as it better captures the social and cultural environments in which mental development ultimately depends.  

A final point is that the neurosciences represent one of the greatest existential dangers to humanity if scientific discoveries are not accompanied by richer discussions of ethics. If we ever reach the point where brain scan technology or medical interventions can, for example, read or change the contents of thought (rather than just measure brain activity), we need to be prepared to discuss the ethical and legal ramifications of those interventions. 

As Grayling’s law states, “Anything that CAN be done WILL be done if it brings advantage or profit to those who can do it.” The corollary, of course, is that “What CAN be done will NOT be done if it brings costs, economic or otherwise, to those who can stop it.” 


The Dunning-Kruger effect, according to, is “a cognitive bias whereby people with limited knowledge or competence in a given intellectual or social domain greatly overestimate their own knowledge or competence in that domain relative to objective criteria or to the performance of their peers or of people in general.” Essentially, when you know very little about a topic, you are blind to your ignorance and therefore overestimate your competence. 

It is only when you begin to gain more knowledge in a subject that you experience the opposite and paradoxical effect of losing confidence in your abilities as you’re exposed to all of the previously unidentified aspects of the subject you now realize you know little about. Education (in particular, liberal education) is, in this way, essentially the process of overcoming the Dunning-Kruger effect and coming to terms with how little you actually know about the world. 

One of the key insights of this book is that this phenomenon does not apply exclusively to individuals. A similar “paradox of knowledge” can be said to apply to humanity in general, in that the more we collectively discover about the world, our past, and ourselves, the more mysteries and puzzles arise in the wake of those discoveries. Whereas we used to think that every advance in our knowledge led to a decrease in our collective ignorance, we now know that the opposite is true.

For example, there was a time, not long ago, when we thought that Isaac Newton had discovered everything there was to know about the universe, and that physics was essentially a closed subject. Promising young physics students were even told to switch careers because there was simply nothing left to discover. 

But then discrepancies in Newton’s theories were noticed based on new discoveries. For instance, when it was discovered that the speed of light must remain constant, this meant that space and time cannot be absolute, as Newton claimed. And so Newtonian physics was, in significant ways, replaced by relativity theory, which in turn may eventually be revised due to its incompatibility with quantum mechanics. Rather than being a closed subject, then, contemporary physics is even more puzzling, with the deep mysteries of quantum physics, dark matter, dark energy, and more yet to be fully explained. 

Regardless of our progress, then, the paradox of knowledge always seems to hold—as we make new discoveries, new problems present themselves, ad infinitum. We are therefore always straddling the frontier between the known and the unknown, which is why it’s always a mistake to assume that our knowledge in any subject is ever closed or complete.

And this is the main message of the book. We must pursue knowledge with a greater sense of humility, guided by reason and evidence, and with a greater understanding of the paradox of knowledge and of our collective ignorance; only then can we overcome the pandemic of dogmatic and inflexible thinking that currently plagues the human mind. 

Recommended Reading

Supplement The Frontiers of Knowledge with A. C. Grayling’s The History of Philosophy for a complete view of the state of all human knowledge: philosophical, historical, and scientific. Also check out The God Argument, which is, in my opinion, the best book to come out of the “new atheist” movement.