FROM ROBERT LAWRENCE KUHN, HOST AND CREATOR OF CLOSER TO TRUTH: Down deep, how does the world really work? Science has made spectacular progress assuming that particles and forces describe all that exists. This principle is called “reductionism,” which means that every physical thing can be explained, deep down, in terms of physics. But take ordinary stuff. Study all its parts separately. What do you get? Not what you expect when you see the whole.
What’s going on? Simple ignorance? Or something more? It seems a mystery and it’s called “emergence.” Somehow, the underlying laws of nature— as we know them—cannot account for the world. So can “emergence” explain reality?
Robert Laughlin, a Nobel laureate in physics, rejects the traditional approach that the way to understand the world is to break it down into little pieces. “Let’s imagine you are on an airplane at 40,000 feet, eating peanuts,” Laughlin begins. “You know that the plane won’t disintegrate; that’s why you’re willing to stake your life on it. It’s a law. Now, where did this law come from? Well, you might say, it comes from atoms, but it doesn’t. The reason we know this is because when you want to find out where the rigidity comes from and you take the metal apart in order to do so, the rigidity vanishes away—the same way the meaning of a pointillist painting vanishes away when you get very, very close to it. In other words, rigidity is something that atoms do together. It’s the ‘togetherness’ of atoms that makes the collection rigid. Laws are relationships among measured things that are always true, and they come about because of organization.”
Laughlin stresses that “lots of things in the natural world have this property that you learn less about them by taking them apart. If you want to know whether your airplane is going to come apart, then you look at these big-scale things, these emergent things. Because that is what matters.”
So it depends on what you want to know. This much seems clear. About some things, one learns less about them by taking them apart. The whole is more than the sum of all the parts. But not all scientists think this way.
Peter Atkins, a world-renown chemist and gifted writer at Oxford University, is a tough-minded reductionist who calls claims of emergence “defeatism.” Emergence, he says, can be an excuse for lack of knowledge. He says that “although we scientists might be reductionists who strip matter down to its fundamentals, we’re actually assemblists.” In his view, scientists “try to understand how properties can be explained from simpler components. … When you understand the pieces really well, you understand the whole. … We wouldn’t dream of bringing sociology to bear on understanding the structure of the atom. But in the opposite direction, we could bring the structure of the atom to bear on understanding sociology. … The whole point about science is the driving optimism that it has. You don’t go into science if you don’t think you can find the answers. And as soon as you start saying we’ll never explain that, you’re no longer a scientist in my view. You become a philosopher.”
Either emergence is key. Or emergence is excuse.
Renowned evolutionary biologist Francisco Ayala says that “while living organisms obey the laws of physics and chemistry, the laws of biology are completely different. They transcend, they emerge. … We have to study life processes on their own level.” He draws an analogy to bricks and houses. “You can’t tell an architect that by studying more and more of the laws of bricks that he will understand more and more how to design a house,” Ayala says. “Sometimes people who claim that physics can explain biology, that atoms and molecules can explain organisms, are confused about ontology and epistemology. You have the bricks and you have the house. You remove the bricks, there is no house. In a human being or in any other organism, you remove the atoms and the molecules, nothing’s left. That’s the ontological question.
“Now, if I want to know about houses, I study the work of architects, not of brick-layers,” Ayala continues. “Studying everything about bricks will never explain very much about houses. Each level of organization has its own laws, and meaningful understanding comes only by studying each and every level on its own terms. Similarly, it’s nice to know about the properties of the atoms, the laws of physics and chemistry, but the things I want to know about organisms are completely different things. That’s the epistemological question.”
Going further, can emergence give us clues as to the basic structure, and perhaps deep meaning, of the universe?
Many scientists, understandably, dismiss such a notion. But to Philip Clayton, a philosopher and theologian specializing in science and religion, emergence is a new way of interpreting the world. He somehow sees emergence as a third way between pure science and fundamentalist religion.
According to Clayton, “emergence is the realization that the natural world is composed of multiple levels, and that as systems get more complex, they don’t just continuously evolve into something new, but at some point in complexity a new type of phenomenon appears which needs to be explained in a different way than that of the lower levels.” This is particularly true of organisms, he states.
I pushed Clayton by asking him the following thought question: “Suppose you were God, so to speak, and you knew every possible detail about every possible particle and force, would you still not be able to predict the properties of higher-level phenomena, particularly of organisms?”
“Even God would have to do some looking at the interactions between organism and environment,” Clayton responded. “Organisms are really responsive to their environment, and so even the omniscient scientist, God-qua-scientist, is going to have to look at interactions.”
According to its proponents, emergence may take two forms. Weak emergence is when clumps of material particles attain a certain degree of complexity so that novel properties “appear”—properties unexpected, at least at our state of understanding, which we could not obtain by simply combining the properties of the individual particles. Weak emergence is the kind of emergence we generally find in physics, where the broader system constrains the behavior of the parts (as in the rigidity of metal).
Strong emergence is when whole entities have causal powers that affect all their parts, causal powers that exceed the sum of the powers of all the parts. Strong emergence adds another dimension and is more controversial. In the case of an organism, Clayton says, “it would be silly to say that its behaviors are just a passive constraint and all of the work is done at the chemical level. An organism is an entity that interacts with its environment in the struggle for survival, and that makes it an active agent. Strong emergence then says that this active agent is a causal force which is causing its parts to behave in a particular way.”
Emergence adherents say that what’s operating here is “downward causation”; the organism exercises causal influence on its constituent parts.
The idea of “downward causation” may sound troubling. Can the actions of the sum of the parts, and nothing but these parts, influence in some nontrivial way the parts themselves in some recursive manner? Clayton claims that at each level of organization, we have new information from the empirical world, but he does not “begin with the dogmatic assertion that we’ll be able to tell the whole story top to bottom or bottom to top in one unbroken narrative.”
As I see it, there is something about whole entities that is indeed more than the sum of all their parts, but one must exercise care in describing just exactly what this means. There is no implicit mysticism lurking here. Emergence is a partial description of how the world works, with unique laws operating at each level of reality that are not “reducible” to the laws of the lower levels. Emergence’s claim, disputed by some, is that reductionism does not always work, and even in principle, there will always be cases in which the laws of lower levels cannot explain the properties (or behaviors) of higher levels. Adherents believe that biology, in particular, cannot be explained entirely by physics.
But as for downward causation, I’m still troubled by that.

Robert Lawrence Kuhn speaks with Robert Laughlin, Francis Collins, Francisco Ayala, Charles Harper Jr., Rupert Sheldrake, Peter Atkins, Philip Clayton, and Stephen Wolfram in "How Can Emergence Explain Reality?" the 28th episode in the Closer to Truth: Cosmos, Consciousness, God TV series, which airs Thursdays on the PBS HD network and many other PBS stations. Every Friday, participants in the series will share their views on the previous day's episode.