For the past decade or so, Friston has devoted much of his time and effort to developing an idea he calls the free energy principle. (Friston refers to his neuroimaging research as a day job, the way a jazz musician might refer to his shift at the local public library.) With this idea, Friston believes he has identified nothing less than the organizing principle of all life, and all intelligence as well. “If you are alive,” he sets out to answer, “what sorts of behaviors must you show?”
First the bad news: The free energy principle is maddeningly difficult to understand. So difficult, in fact, that entire rooms of very, very smart people have tried and failed to grasp it. A Twitter account2 with 3,000 followers exists simply to mock its opacity, and nearly every person I spoke with about it, including researchers whose work depends on it, told me they didn’t fully comprehend it.
But often those same people hastened to add that the free energy principle, at its heart, tells a simple story and solves a basic puzzle. The second law of thermodynamics tells us that the universe tends toward entropy, toward dissolution; but living things fiercely resist it. We wake up every morning nearly the same person we were the day before, with clear separations between our cells and organs, and between us and the world without. How? Friston’s free energy principle says that all life, at every scale of organization—from single cells to the human brain, with its billions of neurons—is driven by the same universal imperative, which can be reduced to a mathematical function. To be alive, he says, is to act in ways that reduce the gulf between your expectations and your sensory inputs. Or, in Fristonian terms, it is to minimize free energy.
To get a sense of the potential implications of this theory, all you have to do is look at the array of people who darken the FIL’s doorstep on Monday mornings. Some are here because they want to use the free energy principle to unify theories of the mind, provide a new foundation for biology, and explain life as we know it. Others hope the free energy principle will finally ground psychiatry in a functional understanding of the brain. And still others come because they want to use Friston’s ideas to break through the roadblocks in artificial intelligence research. But they all have one reason in common for being here, which is that the only person who truly understands Karl Friston’s free energy principle may be Karl Friston himself.
[---]
EVEN FRISTON HAS a hard time deciding where to start when he describes the free energy principle. He often sends people to its Wikipedia page. But for my part, it seems apt to begin with the blanket draped over the futon in Friston’s office.
It’s a white fleece throw, custom-printed with a black-and-white portrait of a stern, bearded Russian mathematician named Andrei Andreyevich Markov, who died in 1922. The blanket is a gag gift from Friston’s son, a plush, polyester inside joke about an idea that has become central to the free energy principle. Markov is the eponym of a concept called a Markov blanket, which in machine learning is essentially a shield that separates one set of variables from others in a layered, hierarchical system. The psychologist Christopher Frith—who has an h-index on par with Friston’s—once described a Markov blanket as “a cognitive version of a cell membrane, shielding states inside the blanket from states outside.”
In Friston’s mind, the universe is made up of Markov blankets inside of Markov blankets. Each of us has a Markov blanket that keeps us apart from what is not us. And within us are blankets separating organs, which contain blankets separating cells, which contain blankets separating their organelles. The blankets define how biological things exist over time and behave distinctly from one another. Without them, we’re just hot gas dissipating into the ether.
“That’s the Markov blanket you’ve read about. This is it. You can touch it,” Friston said dryly when I first saw the throw in his office. I couldn’t help myself; I did briefly reach out to feel it under my fingers. Ever since I first read about Markov blankets, I’d seen them everywhere. Markov blankets around a leaf and a tree and a mosquito. In London, I saw them around the postdocs at the FIL, around the black-clad protesters at an antifascist rally, and around the people living in boats in the canals. Invisible cloaks around everyone, and underneath each one a different living system that minimizes its own free energy.
[---]
The concept of free energy itself comes from physics, which means it’s difficult to explain precisely without wading into mathematical formulas. In a sense that’s what makes it powerful: It isn’t a merely rhetorical concept. It’s a measurable quantity that can be modeled, using much the same math that Friston has used to interpret brain images to such world-changing effect. But if you translate the concept from math into English, here’s roughly what you get: Free energy is the difference between the states you expect to be in and the states your sensors tell you that you are in. Or, to put it another way, when you are minimizing free energy, you are minimizing surprise.
[---]
A single-celled organism has the same imperative to reduce surprise that a brain does.
The only difference is that, as self-organizing biological systems go, the human brain is inordinately complex: It soaks in information from billions of sense receptors, and it needs to organize that information efficiently into an accurate model of the world. “It’s literally a fantastic organ in the sense that it generates hypotheses or fantasies that are appropriate for trying to explain these myriad patterns, this flux of sensory information that it is in receipt of,” Friston says. In seeking to predict what the next wave of sensations is going to tell it—and the next, and the next—the brain is constantly making inferences and updating its beliefs based on what the senses relay back, and trying to minimize prediction-error signals.
So far, as you might have noticed, this sounds a lot like the Bayesian idea of the brain as an “inference engine” that Hinton told Friston about in the 1990s. And indeed, Friston regards the Bayesian model as a foundation of the free energy principle (“free energy” is even a rough synonym for “prediction error”). But the limitation of the Bayesian model, for Friston, is that it only accounts for the interaction between beliefs and perceptions; it has nothing to say about the body or action. It can’t get you out of your chair.
This isn’t enough for Friston, who uses the term “active inference” to describe the way organisms minimize surprise while moving about the world. When the brain makes a prediction that isn’t immediately borne out by what the senses relay back, Friston believes, it can minimize free energy in one of two ways: It can revise its prediction—absorb the surprise, concede the error, update its model of the world—or it can act to make the prediction true. If I infer that I am touching my nose with my left index finger, but my proprioceptors tell me my arm is hanging at my side, I can minimize my brain’s raging prediction-error signals by raising that arm up and pressing a digit to the middle of my face.
And in fact, this is how the free energy principle accounts for everything we do: perception, action, planning, problem solving. When I get into the car to run an errand, I am minimizing free energy by confirming my hypothesis—my fantasy—through action.
[---]
So: The free energy principle offers a unifying explanation for how the mind works and a unifying explanation for how the mind malfunctions. It stands to reason, then, that it might also put us on a path toward building a mind from scratch.
- Free Energy Principle
First the bad news: The free energy principle is maddeningly difficult to understand. So difficult, in fact, that entire rooms of very, very smart people have tried and failed to grasp it. A Twitter account2 with 3,000 followers exists simply to mock its opacity, and nearly every person I spoke with about it, including researchers whose work depends on it, told me they didn’t fully comprehend it.
But often those same people hastened to add that the free energy principle, at its heart, tells a simple story and solves a basic puzzle. The second law of thermodynamics tells us that the universe tends toward entropy, toward dissolution; but living things fiercely resist it. We wake up every morning nearly the same person we were the day before, with clear separations between our cells and organs, and between us and the world without. How? Friston’s free energy principle says that all life, at every scale of organization—from single cells to the human brain, with its billions of neurons—is driven by the same universal imperative, which can be reduced to a mathematical function. To be alive, he says, is to act in ways that reduce the gulf between your expectations and your sensory inputs. Or, in Fristonian terms, it is to minimize free energy.
To get a sense of the potential implications of this theory, all you have to do is look at the array of people who darken the FIL’s doorstep on Monday mornings. Some are here because they want to use the free energy principle to unify theories of the mind, provide a new foundation for biology, and explain life as we know it. Others hope the free energy principle will finally ground psychiatry in a functional understanding of the brain. And still others come because they want to use Friston’s ideas to break through the roadblocks in artificial intelligence research. But they all have one reason in common for being here, which is that the only person who truly understands Karl Friston’s free energy principle may be Karl Friston himself.
[---]
EVEN FRISTON HAS a hard time deciding where to start when he describes the free energy principle. He often sends people to its Wikipedia page. But for my part, it seems apt to begin with the blanket draped over the futon in Friston’s office.
It’s a white fleece throw, custom-printed with a black-and-white portrait of a stern, bearded Russian mathematician named Andrei Andreyevich Markov, who died in 1922. The blanket is a gag gift from Friston’s son, a plush, polyester inside joke about an idea that has become central to the free energy principle. Markov is the eponym of a concept called a Markov blanket, which in machine learning is essentially a shield that separates one set of variables from others in a layered, hierarchical system. The psychologist Christopher Frith—who has an h-index on par with Friston’s—once described a Markov blanket as “a cognitive version of a cell membrane, shielding states inside the blanket from states outside.”
In Friston’s mind, the universe is made up of Markov blankets inside of Markov blankets. Each of us has a Markov blanket that keeps us apart from what is not us. And within us are blankets separating organs, which contain blankets separating cells, which contain blankets separating their organelles. The blankets define how biological things exist over time and behave distinctly from one another. Without them, we’re just hot gas dissipating into the ether.
“That’s the Markov blanket you’ve read about. This is it. You can touch it,” Friston said dryly when I first saw the throw in his office. I couldn’t help myself; I did briefly reach out to feel it under my fingers. Ever since I first read about Markov blankets, I’d seen them everywhere. Markov blankets around a leaf and a tree and a mosquito. In London, I saw them around the postdocs at the FIL, around the black-clad protesters at an antifascist rally, and around the people living in boats in the canals. Invisible cloaks around everyone, and underneath each one a different living system that minimizes its own free energy.
[---]
The concept of free energy itself comes from physics, which means it’s difficult to explain precisely without wading into mathematical formulas. In a sense that’s what makes it powerful: It isn’t a merely rhetorical concept. It’s a measurable quantity that can be modeled, using much the same math that Friston has used to interpret brain images to such world-changing effect. But if you translate the concept from math into English, here’s roughly what you get: Free energy is the difference between the states you expect to be in and the states your sensors tell you that you are in. Or, to put it another way, when you are minimizing free energy, you are minimizing surprise.
[---]
A single-celled organism has the same imperative to reduce surprise that a brain does.
The only difference is that, as self-organizing biological systems go, the human brain is inordinately complex: It soaks in information from billions of sense receptors, and it needs to organize that information efficiently into an accurate model of the world. “It’s literally a fantastic organ in the sense that it generates hypotheses or fantasies that are appropriate for trying to explain these myriad patterns, this flux of sensory information that it is in receipt of,” Friston says. In seeking to predict what the next wave of sensations is going to tell it—and the next, and the next—the brain is constantly making inferences and updating its beliefs based on what the senses relay back, and trying to minimize prediction-error signals.
So far, as you might have noticed, this sounds a lot like the Bayesian idea of the brain as an “inference engine” that Hinton told Friston about in the 1990s. And indeed, Friston regards the Bayesian model as a foundation of the free energy principle (“free energy” is even a rough synonym for “prediction error”). But the limitation of the Bayesian model, for Friston, is that it only accounts for the interaction between beliefs and perceptions; it has nothing to say about the body or action. It can’t get you out of your chair.
This isn’t enough for Friston, who uses the term “active inference” to describe the way organisms minimize surprise while moving about the world. When the brain makes a prediction that isn’t immediately borne out by what the senses relay back, Friston believes, it can minimize free energy in one of two ways: It can revise its prediction—absorb the surprise, concede the error, update its model of the world—or it can act to make the prediction true. If I infer that I am touching my nose with my left index finger, but my proprioceptors tell me my arm is hanging at my side, I can minimize my brain’s raging prediction-error signals by raising that arm up and pressing a digit to the middle of my face.
And in fact, this is how the free energy principle accounts for everything we do: perception, action, planning, problem solving. When I get into the car to run an errand, I am minimizing free energy by confirming my hypothesis—my fantasy—through action.
[---]
So: The free energy principle offers a unifying explanation for how the mind works and a unifying explanation for how the mind malfunctions. It stands to reason, then, that it might also put us on a path toward building a mind from scratch.
- Free Energy Principle
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