How do we go about finding the deepest and truest things about our universe? For centuries, we physicists have been approaching this question from the point of view of reductionism: the idea that we learn the truest and deepest things about the universe by reducing it to its smallest bits. We broke matter down to atoms. Then we smashed atoms together and found they’re made of electrons, protons, and neutrons. And we didn’t stop there. We crashed protons and neutrons into each other and found that they’re made of quarks. And we’re still trying to find all the smallest particles of the universe. This approach is called reductionism. Why are we so enamored with it? Well, partly because of a hope that the converse will also be fruitful: that if we reduce the universe to its smallest bits and how they work together, we’ll be able to build them back up and reconstruct the entire universe.1
When reductionism fails
Reductionism is a framework for pursuing knowledge that has been enormously useful for answering certain questions. But there are many interesting questions that reductionism cannot answer. Think about the Mona Lisa. She’s smiling, but she’s smiling in a subtle way —with her eyes. How did Leonardo Da Vinci make that smile?
Reductionism would say, let’s start with the colors. Let’s do a chemical analysis on the pigments. We’ll break this painting up into the smallest bits and then we’ll be able to understand it. We all know this won’t work. And sometimes reductionism is the wrong approach, even in science.
Few or many?
In my field, condensed matter physics, we research phases of matter, phase transitions (e.g. gas to liquid, liquid to solid), and what electrons do inside of solids. It turns out that electrons inside of materials have many, many more phases of matter than just solid, liquid and gas. Describing those phases is a big part of what condensed matter physics is about. One of the things that we’ve discovered is that when you’re studying large-scale behavior involving many particles, the behavior observed in the whole can be quite independent of the constituents. Think of the drink in your glass or mug. Whether you’re drinking water, coffee, or something else, it’s still liquid. But just three water molecules can’t be liquid: there’s no surface tension and there wouldn’t be enough of them to feel wet. This is one example of a principle called emergence, when analyzing the smallest pieces isn’t the key to understanding the whole.
Emergence happens when large collections of particles exhibit collective behavior that transcends the individual parts. This phenomenon is not confined to physics. If you’ve ever done the wave in a baseball stadium, you’ve participated in an emergent phenomenon. One of the ways that you know you have emergent collective behavior going on is that the behavior has properties that are independent of the individual constituents. For example, if the wave is happening in a stadium, it doesn’t matter whether it’s a baseball stadium in Boston or a soccer stadium in Rio de Janeiro. When the wave happens, it looks more or less the same. And it doesn’t matter whether the fans are tall or short. It doesn’t matter exactly who showed up that day or which team they’re rooting for. There’s something about that wave that transcends its individual components. But not all waves happen because people are standing up and sitting down at the right time. We see waves in other contexts: for example, at the beach or when we hear music by means of compressional waves in the air that carry the sound into our ears. And all these waves look more or less the same. That sameness is an emergent phenomenon that transcends the individual particles.
This idea of emergence opens up some really interesting philosophical questions. But the reductionist story often drowns it out.
The reductionist story
We hear the reductionist idea echoing around society, telling us we’re nothing more2 than a bunch of atoms, interacting through the laws of physics, chemistry, and biology, and that these tiny, microscopic interactions are the only reason I do the things that I do.
The story goes something like this: You and I are made of atoms, and some of those atoms are arranged as DNA. If I understand your atoms and how they work together, and if I understand enough about your DNA, not only can I predict what height you’ll be when you grow up, and what color hair you’ll have, I can even predict who you’ll be as a person, whether you’ll like ketchup or mustard, and why you’ll do the things you do.
But the idea that who we are as humans can be entirely explained by our atoms and by our DNA is a reductionist idea, and while reductionism has given us some great scientific insights, it also failed to tell me why the coffee in my mug feels wet. So what about the emergence story?
The emergence story
We humans are large and complex, larger and more complex than my coffee. If reducing water to its molecules can’t explain why it’s wet, we shouldn’t expect that reducing humans to atoms and DNA will help us be better humans. When we view ourselves through a reductionist lens, as nothing more than a collection of atoms, we devalue ourselves, and we devalue those around us. We can’t let reductionist assumptions dehumanize us. Already, there is a current in studies of consciousness whereby some have concluded that because consciousness cannot be explained via reductionism, it does not actually exist.3
As much as reductionism has been a very useful tool in physics, we’ve seen that it can’t explain basic things like water, and it didn’t help us understand why the Mona Lisa is smiling. Emergence helped us understand my coffee. It reveals the inability of reductionism to account for all large-scale behavior. It gives us concrete (even mathematically provable!)4 examples of how large scale phenomena can transcend microscopic inputs.
So can it also help us to understand the Mona Lisa’s smile? Not entirely.
Emergence reveals that transcendent behavior like a smile defies reductionism. But not all transcendent behavior is emergent. Emergence is about fundamental laws that only become apparent when large collections of things are studied. Because there are laws involved, there is a sense in which it has to be that way: get enough water molecules in a mug under the right circumstances and they will always be wet. But when Leonardo’s brush brought pigments to a fresh panel, the Mona Lisa did not have to emerge.
We cannot explain her smile as either being found in the pigments (reductionism), or as arising from their interactions with the substrate (emergence). The answer to the question of why she is smiling is found in transcendence: the artist, who transcends both pigment and substrate, chose to paint her that way. If her smiling eyes defy reductionism and even emergence, should we think any less of the smile in our own eyes?
Erica Carlson is a Professor of Physics and Astronomy at Purdue University.
- More Is Different, P. W. Anderson, Science, 177, 393 (1972). See also The Theory of Everything, R. B. Laughlin and D. Pines, Proceedings of the National Academy of Sciences, 97, 28–31 (2000). Anderson and Laughlin have both won the Nobel Prize in Physics. ↵
- Not all statements of reductionism include the “nothing more” phrase. See, for example, Ref. 1a ↵
- “Conversations on Consciousness: What the Best Minds Think about the Brain, Free Will, and What It Means to Be Human,” by Susan Blackmore. Oxford University Press, 2007. On pages 8 and 9, the author writes that she is not really conscious, calling it an illusion. ↵
- The Nobel Prize in Physics in 1982 was given to Kenneth Wilson, partly for the development of renormalization group. In this, Wilson proved mathematically that ranges of microscopic parameters can give rise to the same (“universal”) macroscopic behavior. ↵