WHEN YOU HEAR someone arguing that scientific knowledge is limited, you could be excused for expecting to find a creationist or a tobacco industry spokesperson. Instead, here we have a distinguished Ivy League physicist contending that science gives us only a fraction of reality. In The Island of Knowledge, Marcelo Gleiser wants to forge a third way between scientism and obscurantism whereby we can embrace both the power and incompleteness of science.

Many people suggest we should trust science because it is almost finished — final explanations for everything from quarks to consciousness are here or just around the corner. As Gleiser tells us, this is a dangerously distorted perspective. He provides a compelling list of reasons to think that science is not done and, indeed, that it will never be done. Some of these reasons are technical, some conceptual. As our instruments improve, we will see things that we cannot even conceive of now. The limitation of light speed and our particular location in the history of the universe mean that we can only observe a tiny slice of the cosmos. Gödel’s incompleteness theorems and the halting problem keep us from any mathematical road to final truth.

To illustrate the consequences of these limits Gleiser introduces his metaphor of the “island of knowledge.” Like an active volcano, this island is slowly growing as new knowledge is added. We should not think of the island as ever being “done” because we can always add more surface area, even if occasionally a peninsula gets washed away by the rogue wave of a disproving experiment. And as the island grows, the shoreline — the dark edge of our ignorance — continues to expand. A bigger island only presents us with more mysteries.

This means we can never know all the truths about reality and, indeed, that a “theory of everything” is a pointless quest. A “unified theory” is impossible because we will never even know all of the data and ideas that would need to be unified. Gleiser dismisses projects such as string theory as little better than romantic fantasies. Even more strongly, he contends that we have no access to universal knowledge of any kind; we are all trapped in our own little corners of space-time, behind our deeply flawed brains. Even mathematical truths are simply the systems we find useful for solving our particular problems at a particular point in time.

Gleiser wants us to be left with an image of science as an open-ended pursuit: an island that can always expand, not a bucket that is almost full. It can never be finished. We can, and should, push on our limits. Indeed, this book is a compelling call to a new “way of living, a collective aspiration to grow as a species in a world filled with mystery, fear, and wonder.”

Authors of these sorts of books often assume that their expertise in science automatically makes them experts on related historical and philosophical questions. Gleiser nicely avoids this pitfall, referencing and engaging with the relevant humanities literature. It is not every day that one finds a popular science book with an insightful discussion of Mircea Eliade. That said, there are certainly more resources that would have been helpful for the argument. In particular, engaging, say, David Hume’s classic considerations of the limits of science could have significantly enriched the text.

The strongest portions of the book are found near the end, and are sometimes built around autobiographical material. These more reflective sections illustrate Gleiser’s ideas with stories from his own career and work. He gives us moving anecdotes of being inspired to study science by encounters with Uri Geller and Fritjof Capra, and his struggle to find a mentor who shared his passions. It is very helpful to see how his views of science were shaped by his experiences, and how those views in turn shaped his own decisions. This grounds Gleiser’s ideas in the real world of scientific practice, instead of being simply abstract claims.

The first half of the book or so also attempts to accomplish this grounding through analyses of important scientific discoveries and historical ideas. Yet while there are many interesting tales here (and the author does a good job presenting them), it is not always clear how they help advance the book’s argument. Gleiser’s vision of science is often too subtle, and the reader needs a little more guidance in finding it in the historical material. This is somewhat compounded by extremely short chapters (six to ten pages is typical), which make it difficult to fully explore the concepts with which we are presented.

Despite the book’s relentless illustration of the limits of science, the author is clear that he thinks his analysis makes science more robust. We are, he writes, in a time of rampant scientific speculation and arrogance, and this book is his attempt to restrain such tendencies and protect science from overstepping the bounds of its intellectual integrity. This critique is written by a scientific insider, not an external opponent, and it shows.

In addition to curtailing the more epistemologically adventurous scientists, this book makes another important contribution to the public understanding of science. Much of the distrust of science we see in this country today is built around the mistaken belief that science is supposed to be precise, certain, and permanent. Sometimes this is driven by ideology, sometimes not, but there is a common theme: we cannot trust scientists unless they are sure. How can you believe in evolution until the fossil record is complete? How can we act on global warming unless it is established to be 100 percent anthropogenic? Why should I listen to my doctor’s advice when they keep changing their mind on whether eggs are good or bad for me? All these critiques are based on the assumption that complete, unchanging certainty is the proper goal of science. But, as Gleiser compellingly argues, science can never actually provide that certainty. Laypeople often read that lack as an indication that scientists have failed. If you think science is about absolute truth, any revelation of its imperfection seems like a betrayal. The best solution to this problem is to change the initial assumption. If we present science as Gleiser does, as inherently incomplete but still useful, then we can judge scientific claims on their own merits rather than against an impossible standard of Truth. Our “island of knowledge” can be an interesting place to explore even if it does not extend all the way to the horizon.

Gleiser’s metaphor of the “island of knowledge” is evocative, and one wonders how far it can be pressed. Are there other islands out there? Islands dominated by, say, literature rather than science? Could we ever escape our island and go visit another? From Darwin on, biologists have studied closely how organisms migrate from island to island. So what happens when a new idea washes up on the shore of our “island of knowledge”? Island ecologies are fragile. Invasive species ravage ecosystems made delicate by millennia or eons of isolation. Could the same thing happen to “islands of knowledge”? An alien idea that quickly overwhelms our cognitive landscape, rooting out our aboriginal theories the way rats destroy the nests of Galapagos birds?

Perhaps this is a fruitful way to think about changes within science. Instead of Kuhn’s political metaphor of the “revolution,” where an entirely new institution completely replaces a previous one, here we have fierce competition for finite niches. Then, eventually, a new balance forms between invasive and native species. Maybe Copernicanism invaded the island of Aristotelianism, and dominated the lowlands of positional astronomy while the Peripatetics continued to thrive in the highlands of moral philosophy and aesthetics.

Then, if we think of science as an island, we should consider a profound problem of island biogeography: are islands, in fact, islands? The conventional model à la MacArthur and Wilson assumes that there is a genuine isolation at work — the ocean is an impenetrable barrier. But it has become increasingly clear that the shoreline is not a fortress. The water is itself an ecosystem, and interacts constantly with islands. There is no sharp separation. If that is the case with our “island of knowledge,” what does it mean to have limits to science? It is not that nothing lives in the water; rather, there is a transition from land to sea. What is happening in the zone where our knowledge fades into not-knowledge? What are the epistemic equivalents of amphibians or sea birds? We should be alert to the possibility that the limits of knowledge are not well defined, and might be trespassed. Gleiser says there are no lighthouses in the water to show our path, and that may be. But conditions on an island are shaped powerfully by the state of the ocean. And, occasionally, something interesting crawls out of the surf.

It is hard to think about islands without drifting into tropes of exploration — the intrepid voyager charting the mysterious isle. I think this is, in the end, quite consonant with Gleiser’s views. For him, constant exploration is the essence of science. We should be excited that science is limited and provisional, because that means we will never be finished learning. Unsolved mysteries are good things. Without the unknown, we would have no beaches.


Matthew Stanley is an associate professor at New York University, where he teaches the history and philosophy of science.