Chaos theory1 is a field of study in mathematics, with applications in several disciplines including meteorology, physics, engineering, economics and biology. It studies the behavior of dynamical systems that are highly sensitive to initial conditions, an effect which is popularly referred to as the butterfly effect2.
Small differences in initial conditions — such as those due to rounding errors in numerical computation — yield widely diverging outcomes for such dynamical systems, rendering long-term prediction impossible in general. This happens even though these systems are deterministic, meaning that their future behavior is fully determined by their initial conditions, with no random elements involved. In other words, the deterministic nature of these systems does not make them predictable.
This behavior is known as deterministic chaos, or simply chaos. The theory was summarized by Edward Lorenz3 as:
The fluttering of a butterfly's wing in Rio de Janeiro, amplified by atmospheric currents, could cause a tornado in Texas two weeks later.
— Edward Lorenz
The following simple model for population growth might be applied to study fish in a pond, bacteria in a test tube, or any of a host of similar situations. We suppose that the population ranges from 0 (extinct) to 1 (maximum population that can be sustained).
If the population at time
Three lines containing i) the initial density
If
Input:
0.1 1.9 6
Output:
0.1 0.171 0.26934210000000003 0.373914173018421 0.44479449204530547 0.4692094685937818
If
Input:
0.1 3 12
Output:
0.1 0.2700000000000001 0.5913000000000002 0.7249929299999999 0.5981345443500454 0.7211088336156269 0.603332651091411 0.7179670896552621 0.6074710434816448 0.7153499244388992 0.6108732301324811 0.7131213805199696
If
Input:
0.1 4 60
Output:
0.1 0.36000000000000004 0.9216 ... (54 lines) ... 0.977464119602946 0.08811205796713474 0.32139329283172413
A difference of
Input:
0.10000000001 4 60
Output:
0.10000000001 0.36000000003200006 0.9216000000358401 ... (54 lines) ... 0.830632498181969 0.5627286045838009 0.9842604886678766
You may get different results for the final two examples. Different programming languages or computing environments can use different ways to round floating point numbers. These tiny differences cause huge differences in processing the floating point numbers due to the chaotic nature of the model.
As an additional exercise, you can study the difference between using
the formula
The meteorologist Edward Lorenz4 also noticed these effects caused by rounding errors when studying his model of atmospheric convection5. His studies of these effects made him one of the pioneers of chaos theory6.
When a magnitude 6.8 earthquake shook Olympia, Washington, USA on February 28, 2001, shop owner Jason Ward discovered that a sand-tracing pendulum had recorded the vibrations in the image below.
Seismologists say that the "flower" at the center reflects the higher-frequency waves that arrived first. The outer, larger-amplitude oscillations record the lower-frequency waves that arrived later. Norman MacLeod — president of Gaelic Wolf Consulting in Port Townsend — told ABC News7
You never think about an earthquake as being artistic — it's violent and destructive. But in the middle of all that chaos, this fine, delicate artwork was created.