by Daniel Ranard
"I am in the world and at the same time in myself: is there geometry more beautiful?"
When someone learns you're in academia, sometimes they ask questions you're not qualified to answer. An economist friend was asked once: "Oh, so how long do eggs last in the fridge?" And so it is, perhaps, with asking physicists about consciousness. You may as well ask a philosopher, a neuroscientist, or really anyone else – after all, we all have first-hand knowledge of that spark of life inside our skulls.
But I want to write on what physicists think about consciousness. Not because they deserve special authority, but because they provide an important point of reference. The physicist's worldview usually contains some aspect of physicalism (asserting the only "real" things are physical things, governed by physical laws), reductionism (asserting all observable phenomena are explicable in terms of their microscopic parts), and positivism or operationalism (asserting that the only meaningful concepts are empirically testable). And in recent generations more than any others, it seems, this web of attitudes permeates the zeitgeist. It is our inheritance from the success of 20th-century physics.
This inheritance alters the way we frame questions about the mind and consciousness. While Descartes asked how the physical realm interacts with the realm of the mind and soul (his answer: the pineal gland), today we immediately privilege the physical. If the world consists only of the physical, how does the conscious mind arise? If your brain is a soup of electrons and protons, how does this soup come to harbor an interior experience? What gives rise to thoughts, feelings, and sense of being?
Philosophers have devised an intricate taxonomy of responses to the question of how consciousness relates to the physical world. Where do modern physicists fall within this taxonomy, especially as a community whose attitudes have historically shaped the framing of the question?
We might as well start Edward Witten, a theoretical physicist who already serves as something of an oracle within the field. In fact, when he speaks among physicists, it's often accompanied by a hush in the room. So here's Witten, in a video interview:
I think consciousness will remain a mystery… Understanding the function of the brain is a very exciting problem, in which probably there will be a lot of progress during the next few decades. That's not out of reach… But what it is we are experiencing when we are experiencing consciousness, I see as remaining a mystery….
In short, Witten subscribes to:
View #1: "It's a mystery – that's all I can say."
Anticlimactic, maybe. But a strength of science is that its wisest practitioners only make scientific claims when they are capable of addressing a question scientifically. Witten is careful to distinguish two different types questions about the mind. One can first ask: what are the inner workings of the brain, physically and biologically, and how do these give rise to behavior? Like most physicists, he assumes that scientists will eventually answer this question. The brain is a complicated physical system, but it's governed by the same laws as all other matter. Meanwhile, there's the second question of how the brain gives rise to conscious experience. What is the nature of your interior world, and how is it related to physical matter? This question Witten is unwilling to answer. Many physicists share his agnosticism.
It may seem Witten hasn't said very much. But at least he maintains there's some mystery. Compare that with:
View #2: "There's no mystery – there's no mind, only matter."
The physicists' legacy of physicalism frames popular questions about consciousness. If you believe the world consists of only the physical, then consciousness will present a puzzle: how do you account for the mental realm we inhabit? We have seen that one response is to claim agnosticism. But another is to stick hard to physicalism. Such hardline physicists account for the mental realm by simply denying it, or denying the validity of the question. Their view is something like what philosophers call eliminative materialism. It stems from the long and fruitful scientific tradition of only asking questions that can be empirically verified. You don't ask, "What's an electron really like?" or "What is the essence of the quark?" These questions are dismissed as not only useless but also truly meaningless, questions about nothing. Instead, one asks, "What happens when you measure the electron in the following way?" Likewise, many physicists reject typical questions about consciousness. If the ineffable interior life of conscious beings is not something we can ask valid questions about, then does it really exist?
To these physicists, you can't ask, "What is Alice really feeling inside her head?" — a question with no verifiable answer. Instead, you ask questions like, "What will Alice say when I ask her what she's feeling inside her head?" The second question does have a verifiable answer, and one that you could hypothetically predict using the laws of physics, assuming you can solve the equations governing the particles that constitute Alice, calculating how her mouth will move in response to the question. Physicists with View #2 will satisfy themselves with questions of the latter nature, while dismissing questions of the former. To them, the "mind" is just another sort of abstraction, a useful bit of language. The question of how the mind arises from the brain is no more philosophically troubling for them than the question of how a "cloud" arises from a collection of water molecules hanging in the sky.
View #2 can be hard to stomach. To many of us, it certainly feels like there's something special going on inside our heads. It feels like our thoughts have a special sort of existence that clouds don't have. If one accepts that intuition, it leads the physicist to:
View #3: "Consciousness is a mysterious property that emerges in certain physical systems."
For these physicists, it's possible to admit that consciousness is a special sort of phenomenon that occurs in certain physical systems. Particles arranged in the shape of a table aren't conscious, but particles arranged in the shape of a person usually are. Somehow, a particular motion of particles gives rise to a special interior world, a mind. At the same time, one can maintain that this "mind" has no causal control over the matter that composes it: it's what philosophers call an epiphenomenon, a phenomenon outside of the causal order. Many physicists are somewhat epiphenomenalists, I think. If you accept that the mind is real and not some simple abstraction, and you believe it's a consequence of certain physical arrangements of matter, the question becomes: what arrangements of matter give rise to consciousness?
This question may be difficult, but at least it is (some believe) meaningful. One physicist who's taken a stab at the question is Max Tegmark from MIT, in his speculative paper "Consciousness as a State of Matter." I won't claim Tegmark is an epiphenomenalist of otherwise classify his philosophy, but he does ask the question: which sort of matter is conscious, and why? For a critical look at some related ideas, I also recommend the analysis of Scott Aaronson, a theoretical computer scientist and part-time physicist.
I suspect that Views 1, 2, and 3 loosely cover the majority of physicists. Then again, maybe you're better off asking the economist how long you can leave your eggs in the fridge.