Decoherence, or What is Special About a Tree

Quantum physics makes some people – especially those that seem to understand it – uncomfortable. It suggests that at the base of reality, things can be both here and not here, both particle and wave, both one and zero. The double slit experiments, in which electrons are sent in groups or individually through screens with slits open or closed, show wave or particle features depending upon the experimental set-up. Anything, small or large, can be thought of as existing as a wave function with the probability that when measured the wave will collapse into a definite object in a specific place as determined by the probabilistic mathematics. (Large objects have the highest probability of being where we see them, when we see them, rather than anywhere else the wave may be spread out to, including perhaps in another galaxy.) The picture of reality that quantum physics paints is strange yet the mathematics of it – quantum mechanics– successfully predicts core elements confirmed by experimentation. Niels Bohr, who was at the forefront of inventing the mathematics, said that it requires a “radical revision of our attitude toward the problem of physical reality.” For Bohr, and others of the Copenhagen school, the relationship of quantum physics to classical physics – the micro world to the macro – is not straightforward. Quantum mechanics accurately predicts outcomes at the level of the very small where quantum affects lead to strangeness. Yet we seldom see quantum effects at the macro level that is well-described by classical physics, despite its failure at the micro level.

One of the stranger possibilities raised by quantum physics is the role of the conscious observer. This interpretation posits that a wave function is collapsed when measured and the measurement observed. (The role of the measuring instrument and whether it is part of quantum or classical reality is one of the many issues still debated.) Various efforts have been made to sweep aside the difficulty of reconciling quantum and classical physics and avoid the messiness of assuming a tree is not there unless someone sees it. (This problem is separate from attempts to reconcile quantum physics with relativity or to unify the fundamental forces and particles of nature.) One such – the many worlds theory – suggests that every time a measurement is made, reality splits into separate universes. A more parsimonious approach looks to the concept of quantum decoherence. Essentially, wave functions spread out into each other and merge into the world of classical physics. Strictly speaking, this still leaves the question of the role of measurement and the observer open. But some believe we need not accept any quantum strangeness because decoherence itself leads to macro objects emerging from the micro reality. The quantum waves crash onto the shores of observability by themselves. A tree is there whether we see it or not.

The questions here are profound. One hundred million years ago, the earth was populated by dinosaurs. Some very large creatures roamed the earth and we have found their bones in our time. Surely they existed and moved through space and time as discrete objects. They stepped over stones and across rivers that also had a specific and real existence. Even before that, in deep time, before multi-cellular life, primitive bacteria and archaea lived and reproduced and we’ve found their traces as well. They existed without being measured or observed by any higher, conscious living being. So does this mean that quantum strangeness is fake physics?

The possibilities seem to be three:

– quantum mechanics works well at the micro level but is unnecessary to explain the reality of the world we see because it emerges on it’s own whether we are there or not to see it.

– nothing emerges from the universal wave function (the equation encompassing the totality of existence across time and space) as discrete objects until observed.

– some things exist as collapsed wave functions on their own while other “things” exist only as the former interact with them.

The first possibility simply begs the question of how two fundamentally different pictures of reality can both be true. Rather, let me suggest that the second possibility may be a subset of the third. Life is the dividing line. Rocks, planets, stars and even galaxies exist as wave functions perhaps decohering as they spread out into each other but still not there until acted upon – observed, eaten, stepped on – by something acting as an individual agent, something alive and trying to stay alive and perhaps reproduce. Life seems inevitable given the fundamental constants of physics and chemistry. (Why the universe is made this way is a separate question.) But a rock is just a rock and is never trying to become anything else. It may be acted upon but doesn’t by itself act. A tree is always there because it is trying to be. It acts upon its surroundings with purpose thus collapsing its own wave function and those with which it interacts. It transforms earth and sunlight into living tissue, its own living tissue. This may imply or even require a certain kind of consciousness. Certainly, it does suggest awareness of environment sufficient to utilize it. How is a tree’s awareness different from our own? That is another matter. But a tree is there even if alone its forest.

Plants and the Sun

There's a fascinating article in the New Yorker on The Intelligent Plant.  It looks at the current debate among plant scientists over whether plants are intelligent or might be said to behave intelligently.  Plants do seem to interact with their environment in a way that appears directed and can often be quite complex.  But what caught my eye was the statement by one scientist to the effect that one does not have to ascribe intelligence to plants just to make them sound special as it's enough simply to note that they "eat sunlight."

We all learn about photosynthesis in school.  How sunlight is converted to free electrons within plant chloroplasts and made available to make carbohydrates from air and soil.  This is indeed wonderful enough.  But the notion that what plants are doing can be simply described as eating sunlight brings to the fore just how miraculous a process this really is.  Plants eat sunlight and we animals can then eat them and those that eat them for us.  Through the intermediation of plants, we too eat sunlight.  And it's free.

On a recent warm, sunny winter solstice day, sitting outside smoking a cigar, I looked anew at how this system works.  The universe is constructed in just such a way as to allow complex physics and chemistry to evolve giant balls of gas that release tremendous fountains of energy -- we call these stars, like our sun -- free to be consumed by stationary processing plants -- that we indeed call plants -- to also feed mobile creatures that may eventually achieve individual consciousness. 

Pretty cool.