A View From the Top

In the 1970s, there were two George F.R. Ellises. One was a freshly-appointed professor of applied mathematics at the University of Cape Town, a prolific writer on space, time, and relativity, and the author, with Stephen Hawking, of a soon-to-be-classic treatise on general relativity.

The second George F.R. Ellis was a thorn in the side of South Africa’s Nationalist government, a sharp-tongued critic of apartheid, and an advocate for policy reforms that would ease the flight of South Africa’s poor and homeless.

"I ran various organizations in a complex social environment and encountered all the problems that entails," says Ellis. "This gives a unique viewpoint in that I try to have a worldview that encompasses both worlds." And where these worlds intersect, Ellis has found the inspiration to take a fresh look at how physicists think about the nature of causality. His work turns conventional ideas of information flow on their head and could have repercussions on our understanding of the origin of life.

It’s been said that human beings can be reduced to biology, biology to chemistry, and chemistry to physics. In this reductionist view, it is possible in principle to completely understand the complex tangle of human society—love, friendship, politics, the whole shebang—as the interaction of so many subatomic particles (or, for the string theorists in the audience, vibrating strings). Through a densely layered hierarchy—strings become particles, particles become atoms, atoms become molecules, molecules become neurons, neurons become brains, brains become societies—these fundamental building blocks cause everything in the universe to happen, from the bottom up.

Two-Way Street

But to Ellis, this view of reality falls short. As he began reflecting on social policy in the 1970s, he saw a society that was profoundly influencing the individuals within it, and not the other way around. If societies influence brains—and, thanks to the new science of neural plasticity, modern neuroscientists can see this in action—then societies can also influence neurons, molecules, atoms, and subatomic particles, taking us all the way down to the bottom of the physical hierarchy. Causation, Ellis saw, is not a one-way street: It goes from the top down just as easily as from the bottom up.

Now, Ellis has distilled this idea in an essay for FQXI’s 2012 "Questioning the Foundations" essay competition. Ellis’ work, "Recognising Top-Down Causation," received second-prize honors. But his thinking of the subject stretches back further: Ellis has been writing about top-down causation since 2004, and in 2011 he organized a conference on the theme, held in London, UK. He’s now developing a book on the subject.

Consider the case of a computer, says Ellis. Seen from the bottom up, a computer is nothing more or less than the movement of electrons from one place to another. Seen from the top down, a computer begins with a human user, who uses keystrokes or mouse clicks to make inputs. Those inputs travel down the physical hierarchy, setting electrons in motion, which ultimately travel back up the chain to create changes—say, a new Facebook status—that the computer user can see on screen. The bottom-up view isn’t wrong, in Ellis’ view; it just isn’t the whole story.

Another example is a jumbo jet: "Human minds worked in a top-down way to configure billions of atoms that created this reality," says Ellis. "If you don’t believe in top down causation, you have to believe the jumbo jet came into existence by magic: The constituent atoms certainly did not spontaneously self-assemble to create the aircraft."

Now, Ellis hopes to elucidate exactly how top-down causation works. "A first key point is that top down causation does not work by any magical powers, it works by setting constraints on lower level functioning," says Ellis. For instance, as Ellis describes in his essay, the density of matter and energy in the cosmos puts limits on the outcome of nuclear reactions through a chain of events that travels from the most "macro" to the most "micro." Similarly, the activity of supermassive black holes, which churn at the centers of most galaxies, can put a check on the rate at which stars form and therefore, on an even more micro level, the rate at which individual atoms undergo nuclear fusion.

Ellis also believes that unraveling and quantifying the mechanisms of top-down causation may illuminate some of the thorniest questions in science, beginning with the quantum measurement problem: how the intervention of a macroscopic observer "collapses" a quantum wavefunction, which represents many possibilities simultaneously, into a single measured outcome. (See also "The Crystallizing Universe.")

But the idea goes against the grain of thousands of years of physics and philosophy. "The notion that everything is made of simple components (atoms) and that by understanding those components you can understand the whole" goes back at least to ancient Greece, says Paul Davies, a physicist at Arizona State University (ASU). The idea of top-down causation, on the other hand, appeared in philosophy circles just a few decades ago, and has received a mixed reception in both the physics and philosophy communities. "Hard-nosed reductionists," says Davies, do not tolerate the idea at all.

Yet even some thinkers who believe that the universe can ultimately be explained in a bottom-up fashion are finding that top-down causation is a useful idea. Ellis and others take a harder line still, arguing that top-down thinking is more than a pragmatic abstraction: It is an essential piece of how the universe functions. One supporter of the idea is astrobiologist Sara Walker, also at ASU, who is applying this idea to one of the most vexing problems in science: the origin of life itself. Walker is investigating how non-living systems transform into what we call life. She believes that the key may be an inversion in the flow of information. In non-living systems, information only goes from the bottom up. But in living systems, it can travel from the top down, too. "My work has been really inspired by what George is doing," she says.

Signs of Life

This novel definition of life could give astrobiologists searching for "life as we don’t know it" a new way of thinking. After all, our current definitions of life are intrinsic to the biology we know, like the specialized chemistry of DNA, Walker explains: "If there’s non-DNA life, even on Earth, we won’t find it right now. We need a more universal definition of living systems." Establishing that definition will require a deeper understanding of how top-down causation operates. "We need to push for the idea that top-down causation is a physical thing, and try to quantify it," says Walker.

But these are, of course, early days. "The first step in turning this in to something more than philosophy is to give it some mathematical rigor," says Davies. "Can we demonstrate this in at least a semi-rigorous mathematical model? Otherwise, it’s just essays, essays, essays!" Davies believes that Ellis may be just the person to take top-down causation from the realm of philosophy into the realm of quantifiable, and testable, science. What distinguishes Ellis is his intellectual toughness combined with a "strong philosophical streak," says Davies. "George is a careful, rigorous thinker, but it doesn’t preclude him from thinking about these bigger issues."

Indeed, Ellis is not satisfied with philosophical musings. For his project to be successful, he says, it needs "to carefully identify relevant mathematical formalisms, and where in those formalisms top-down causation can be identified as occurring." It also must pass the most basic test of science: making novel, verifiable predictions. "Some people try to redefine reality to fit their theories. They live in two worlds: a reductionist-based world in the laboratory, and a complexity based world at home, and they don’t mesh properly together," says Ellis. But he has always believed in one world: A world where a scientist and a crusader, a philosopher and a policy wonk, can be one and the same man. A world where there are not two George Ellises but just one, struggling to make sense of the universe from atoms to civilizations and back again.