People and the Cosmos: Constructor Theory

It seems that, as soon as our ancestors could afford to, they added a spiritual dimension to their existence. Human burial practices are at least 100,000 years old, and religious ceremonies date back at least 50,000 years. Though interpretations vary, it is thought that the famous archeological site called Gobekli Tepe is the oldest ritual site ever discovered. This Turkish site is thought to have been constructed around 10,000 BC—not by city-dwellers, or even by settled agriculturalists—but by nomadic hunter-gatherers. This implies that such people satisfied their spiritual needs before settling down and building the great early civilizations of Mesopotamia. The Biblical Matthew, with his famous line “Upon this Rock, I will build my Church,” may have got things backwards.

Cave paintings that reveal a reverence for animals and the Greek constellations named after divinities suggest that our forebears lacked the explicit distinctions between the sky above our heads, the fauna that roam the Earth and ourselves that we take for granted today—it has taken centuries of scientific investigation to make the fundamental differences between these realms obvious. The terrestrial, celestial and human were intertwined in the magical stories our prescientific ancestors told themselves.

In humanity’s earliest theories of the world, then, people played a fundamental role.

But, with the dawn of the scientific revolution in the sixteenth century, such anthropocentrism grew less plausible—first, in 1543, Copernicus overthrew the geocentric model of our Solar System, and then, in 1687, Isaac Newton published his Principia Mathematica. Newton offered a bold new worldview, in which the motions of objects from pebbles to planets could be both explained and predicted—tell me the current position and velocity of an object, along with the forces acting on it, and I’ll give you its position and velocity at any later point in time. Copernicus—and later Galileo— demonstrated that the Earth was not at the center of the Solar System. Newton robbed our ancestors of their innocence by proposing the first universal theory, which explained phenomena across all of time and space in purely physical terms—magical and religious thinking were banished from his predictable, clockwork universe. Humans, it seemed, played no special role in this new understanding of reality.

But it was not obvious how Newton’s theory of classical mechanics applied to living things. After all, predicting the trajectory of a cannonball was far easier than predicting the flight pattern of a bird. Moreover, none of this new physics had anything to say about the intricate design of living creatures. So people could still take refuge in the fact that humans were created in God’s image—there was still no explanation of our apparent design, let alone our ability to comprehend the cosmos.

But then along came Darwin and our ancestors took another step towards adulthood. In Darwin’s theory of evolution by natural selection, all the apparent design in the biosphere has emerged through a long, long chain of slight modifications passed down from generation to generation. Those changes, which we now understand as due to mutations in the genetic code, were more likely to be passed on if they increased an organism’s fecundity—its ability to produce offspring—who, in turn, survived and reproduced. (The modern incarnation of Darwinian theory considers genes, not organisms, as the fundamental replicators.) The organism’s environment was a selector, a ruthless arbiter that determined which organisms were more likely to reproduce, and which were more likely to be tossed into the dustbin of extinction. String together enough of these cycles of random changes and non-random selection, and the result is all the elegant design and order in the biosphere.

There was no getting around it—this process explained the evolution of humans, too. Apparently, the story behind the emergence of algae and cattle also explained our entry onto the world stage. There was no room for the exceptional status of our species, which many had hoped biology would preserve.

So, after only a few centuries of modern science, the role of people was diminished on all fronts. We are not at the physical center of our Solar System, nor of our galaxy. We are not mentioned in any of our profoundest physical theories, which present a world that conforms to exact laws of motion and can be predicted with certainty. And even our best theory of life implies that we came about by the same naturalistic process that brought about every other apeish creature. Anthropocentrism, it seemed, was a thing of the past, a relic of a less mature people.

But then came a new theory of reality, one that cannot be readily dismissed. A few years ago, physicist David Deutsch published a foundational paper on what he calls constructor theory. Since Newton, our best theories in physics have followed the paradigm he established—given the state of a system, a theory ought to predict its state at any future time. The details of what a state is depend on the particular theory involved, but in general this has been the prevailing conception—in Deutsch’s own phrase—since Newton’s first great universal theory.

Constructor theory’s fundamental principle is that the laws of physics can be viewed in terms of transformations, which are either possible or impossible. So, if Newton’s theory tells you the trajectory of a projectile, given some initial position and velocity, constructor theory asks which trajectories are possible in principle, according to Newton’s theory.

The switch from thinking about a system’s particular transformation from one state to another to asking what transformations are possible in principle represents a radical shift in perspective. This new, deeper worldview goads us into asking questions that wouldn’t have been conceivable under the previous, Newtonian framework. If we may describe the world in terms of possible transformations, rather than particular trajectories, then which objects may cause such transformations, and which can’t, and why?

People have converted rocks into cathedrals. They’ve mixed the fiery energy of the sun with the guts of Earth itself to produce the orderly, purposeful devices that prevail in our digital age. They’ve turned wolves into dogs, trees into books and metal into vehicles that fly through space.

None of these transformations happen spontaneously in the universe. They require the presence of people—entities capable of facilitating any transformation permitted by the laws of nature, so long as they know how to achieve it. In describing how reality works, then, one must take people into account.

It’s taken a few centuries, but we’ve come back to the ancients’ view of the relationship between people and the cosmos. While we’ve rightly abandoned the majority of their beliefs, they were right about this much—to understand nature at its deepest, we have to acknowledge the special role people play. When predicting the motions of the planets, or explaining the origins and evolution of life, people are irrelevant. But it is people, and only people, who are the ultimate transformers of this vast and wondrous cosmos. May our descendants use this power to create an ever more beautiful reality.