Stability analysis asks such questions as: will the system return to its condition prior to the disturbance, the state of equilibrium? Will it settle down into a different condition? Or will it spiral out of control in a state of chaos, a classic example of an unstable process? It is a fundamental principle of science that hypotheses about the physical universe should be verified by observable data collected in experiments before a physical law is established.

But how do we ascertain a system's stability or take measures to stabilise it unless we can observe, measure, and influence the system's behaviour?

In large, complex and interconnected systems like power generation and transmission networks, blackout and breakdown are often a consequence of an undetected local disturbance that quickly spreads to the wider network. That disturbance might also be an unforeseen catastrophe, as in the recent tsunami damage to nuclear reactors in Fukushima, Japan, where data on the reactors' nuclear core was limited and measures to control the meltdown were by trial and error. Thus, it is important for the stability of a system that one can control and observe its internal structure and performance .

Increasingly, stability analysis is being applied to economic, social and political systems, as well as biological systems. We are now constructing mathematical models and using analytical methods to study the stability of such systems as population growth, ecosystems, and weather forecasting.

We are even making use of the concepts to analyse social and political systems, though these systems are difficult, if not impossible, to quantify.

Society can be viewed as a dynamic system that connects its stakeholders - citizens, civic groups, government, and so on. Tension exists: some forces resist change and attempt to maintain the status quo within certain limits that they believe allow its stable operation. Some forces promote change.

Sometimes the restraining force dominates and a society maintains its equilibrium state for a long time. At other times, a disturbance, internal or external, will be large enough to move society to a different equilibrium state within a short time, perhaps violently. The challenge is in understanding and managing the domain of stability, and to recognise the extent to which a society can remain in equilibrium or be migrated to a different one through policy initiatives without a chaotic transition.

Democracy is often described as a political system with the capacity to stabilise a society quickly in the face of social unrest, whereas the recent uprisings in various Middle East autocracies point to those regimes' inherent instability. In the collapse of the Soviet Union, an unstable political system, a disturbance in the form of glasnost and perestroika moved the USSR from a single-nation equilibrium state to a 15-nation configuration, each having its own equilibrium state, with considerable chaos during the transition period.

The debate on nation-building in Iraq and Afghanistan is framed as whether stability in those countries can be achieved by external effort despite their social and political dynamics being neither fully observable nor controllable.

The return of Hong Kong to China in 1997 under the 'one country, two systems' principle was a massive disturbance to a social and political system that had been in place for over 150 years. Afterwards, severe external disturbances struck Hong Kong: the Asian financial crisis in 1998, the Sars epidemic in 2002 and the global financial crisis in 2008.

Viewed through the prism of system and stability theory, Hong Kong is still experiencing the after-effects of those disturbances and a new equilibrium has yet to emerge. However, the resilience of the existing administrative infrastructure provides the stabilising mechanism that allows Hong Kong to move along a relatively stable trajectory. Yet, worsening socio-economic conditions such as unaffordable housing, an ageing population, and income disparity have the potential to move Hong Kong from into the unknown .

And while China has recovered from 150 years of decline to become the world's second-largest economy with increasing international leverage, the one-party system with a lack of checks and balances is arguably in a state of unstable equilibrium that is precariously maintained by the application of overwhelming government force. An unstable dynamic system maintained by the application of external force, will sooner or later implode unless changed to a more stable state.

The human body is probably the most sophisticated system that is able to adjust to disturbances, such as injury, infection and trauma, by repairing itself and returning to a stable state of health. When an injury or illness is too severe, the body may not adjust and move on to the ultimate state of equilibrium: death.

The body politic is no different.

Tom Yam, a Hong Kong-based management consultant, holds a doctorate in electrical engineering and an MBA from the Wharton School of the University of Pennsylvania. He has worked at AT& T, Ernst & Young and IBM