In collaboration with Keith Mott, a plant biologist at USU, and several graduate and undergraduate students, I am developing methods to quantitatively identify and characterize how plants manage to solve sophisticated problems. One of our typical reflective moments is shown below.
If you are not a plant
biologist (and perhaps even if you are), you may be surprised to learn that
plants are capable of solving subtle problems. But itÕs true.
Each day, a plant is faced with the dilemma of trying to acquire as much
CO2 as possible from the atmosphere (which it then uses to store energy via
photosynthesis), while at the same time trying to mitigate the possibly
deleterious effects of excessive water loss (via evaporation).
The hardware a plant uses to
regulate the exchange of gases between the air and its interior are variable
aperture pores – stomata
– that cover the surfaces of its leaves. Bright light causes a plantÕs stomata to open, and this, in turn,
permits CO2 to enter the leaf and water vapor to leave.
Because water evaporation
increases as temperature increases, a straightforward strategy for maximizing
CO2 uptake while minimizing water loss would seem to be: open stomata wide when
itÕs cool, close them shut when itÕs hot.
This is where the subtlety comes in. Even when a pore is wide open, CO2 can only enter a leaf at
a limited rate because CO2 molecules have to diffuse through air. Thus, to maximize CO2 uptake over the
course of a day requires that pores be open to some degree all of the
time. So, what is the correct
openness for each temperature, humidity, and light level condition?
Keith and I believe that
plants may solve this complicated
problem by a process called Òemergent computation.Ó Much more about how stomata work, what emergent computation
is, and what the evidence is for plants performing emergent computation can be
found at our Complexity
and Stomatal Behavior web site.
The work I have done on
uncovering possible computation in plants is a part of a larger interest
centered on the question, are the behaviors of natural systems the result of
formal computations? Among other
things, computation seems to involve the deterministic manipulation of
information to perform a purposeful task.
So, then, is a falling rock a computation? When a rock falls, its trajectory is determined by some
initial data (the rockÕs initial position and velocity) and by the requirement
that a quantity called the ÒactionÓ be a minimum. In other words, the trajectory of a falling rock is a set of
output data that Òsolves the problemÓ of minimizing action. Sounds kind of like a computation. Still, a falling rock doesnÕt seem very
subtle or sophisticated. IsnÕt
falling Òjust the way it is?Ó
Trying to figure out how to
tell when a phenomenon is a sophisticated computation and when it is Òjust the
way it is,Ó is my current major research interest.
Relevant Publications: