Neuroscientist, UC Santa Barbara; Author, Tales from Both Sides of the Brain
The Schnitt

For all our scientific efforts, there remains a gap, the Schnitt. The gap between the quantum and the classical, between the living and the non-living, between the mind and the brain. How on earth is science going to close this gap, what the physicist Werner Heisenberg called the Schnitt, and what the theoretical biologist Howard Pattee calls the “epistemic cut”? Some maintain the gaps only reflect a current failure of knowledge. Others think the gaps will never be closed, that they are in fact un-closeable.

Pattee, who has been working at the problem for fifty years, believes he has a handle on it. I think he does too. The clue to grasping his idea goes all the way back to understanding the difference between non-living and living systems. To understand this difference, biologists need to fully embrace the gift from modern physics, the idea of complementarity.

Accepting this unexpected gift is not easy. Einstein himself wouldn’t accept it until Niels Bohr forced him to. The discovery of the quantum world meant the classical world of physics had a new partner that had to be considered when explaining stuff. Suddenly, the world of reversible time, the notion of dogmatic determinism, and the aspiration to a grand theory of the universe were on the rocks. Bohr’s idea, the principle of complementarity, maintains that quantum objects have complementary (paired) properties, only one of which can be exhibited and measured and, thus, known, at a given point in time. That’s a big blow to a scientist, and to physicists it is perhaps the most devastating. As Robert Rosen pointed out, “Physics strives, at least, to restrict itself to "objectivities." It thus presumes a rigid separation between what is objective, and falls directly within its precincts, and what is not.… Some believe that whatever is outside is so because of removable and impermanent technical issues of formulation…. Others believe the separation is absolute and irrevocable.”

This is where Howard Pattee picks up the story. Pattee argues that complementarity demands that life is to be seen as a layered system in which each layer has, and indeed demands, its own vocabulary. On one side of the Schnitt, there is the firing of neurons. On the other, there are symbols, the representations of the physical that also have a physical reality. Only one side of the Schnitt can be evaluated at a time, though both are real and physical and tangible. Here we have Bohr’s complementarity on a larger scale, two modes of mutually exclusive description making up a single system from the get-go.

There is no spook in the system introduced here, and Pattee calls upon the venerable mechanisms of DNA to make his point. DNA is a primeval example of symbolic information (the DNA code) controlling material function (the action of the enzymes), just as John von Neumann had predicted must exist for evolving, self-reproducing automatons. However, it is also the old chicken and egg problem, with fancier terms: Without enzymes to break apart the DNA strands, DNA is simply an inert message that cannot be replicated, transcribed or translated. Yet, without DNA, there would be no enzymes!

Staring us right in the face is a phenomenal idea. A hunk of molecules, which have been shaped by natural selection, makes matter reproducible. These molecules, which can be stored and recalled, are a symbol, a code for information that describes how to build a new unit of life. Yet those same molecules also physically constrain the building process. DNA is both a talker and a doer, an erudite outdoorsman. There are two realities to this thing. Just like light is a wave and a particle at the same time. Information and construction, structure and function, are irreducible properties of the same physical object that exist in different layers with different protocols.

While I find this a tricky idea on the one hand, it is utterly simple and elegant on the other. Pattee has given us a schema and a way to think about how, using nothing but physics (including the principle of complementarity), life comes out of non-living stuff. The schema, way up the evolutionary scale, also accounts for how the subjective mind can emerge from objective neurons. Pattee suggests that instead of approaching conscious cognition as either information processing or neural dynamics, there is a third approach available. Consciousness is not reducible to one or the other. Both should be kept on the table. They are complementary properties of the same system. I say hats off to Pattee. We brain scientists have our work cut out for us.