Complexicon: Resilience

Dr. Seth Blumsack explains the concept of resilience as it applies to complex systems!

Resilience refers to the ability
of a dynamical system

to return to its original
state and function

after being disturbed
by some external force or event.

A system that is resilient will return
to its original state and function,

while a system that is not resilient
will instead settle to a new equilibrium

that was different from
the original state of the system.

So imagine you take a marble
and you put it inside of a bowl.

Now poke the marble
a little bit. Not too hard.

The marble rolls around the bowl
and settles back down to the bottom.

We would say that this system was resilient

to the slight nudge that you gave the marble.

Now push the marble really hard,

so hard that it slides right out of the bowl
and lands somewhere else.

In this case our dynamical system
is not resilient.

The force that pushed the system was so large

that the system itself landed
in a new equilibrium state,

in this case, the marble being outside of the bowl.

We often depend on natural
and engineered systems to show resilience,

the ability to return to normal
after being disturbed.

Examples include critical infrastructures,
like bridges and power grids,

and ecosystems like
forests, lakes, and wetlands.

Whether a system is resilient or not

often depends on the existence
of thresholds in dynamic behaviour.

A threshold is a point
at which there is a sudden change

in the behaviour of a system

or a point where small disturbances

can cause that system
to respond in big ways.

Identifying thresholds
without having to live through them,

or finding early warning signs

of systems approaching thresholds,

like earthquake or tsunami warning systems

or tipping points in the Earth's climate system,

is an ongoing scientific challenge

that spans ecology, engineering,

statistics, and many other scientific fields.

We often think of resilience as being a good thing.

After all, no one likes power blackouts

or the collapse of entire ecosystems

on which people depend.

We want our power grids
to be able to withstand the stress

that comes from severe weather
or overloaded equipment.

But a dynamical system being resilient

is only a good thing if we're happy
with the state of that system.

There are several examples
of social and engineered systems

that have self-reinforcing feedbacks, or hysteresis,

keeping them in equilibrium states
that we might find uncomfortable.

Examples include social systems
that promote racial inequality,

or energy systems that reward
the use of polluting fuels.

In these cases we might want
to encourage system instability

and transition to a new state
rather than accepting resilience.