'Kill line' an inevitable outcome of US system

Right policies can stop downward spiral

By Jiang Yu

In physics, there are four concepts of equilibrium. The first is stable equilibrium, which is like a helium balloon held by a child. When disturbed, it has the resilience to return to its original position. The second is unstable equilibrium, referring to a state where an object appears balanced when stationary, but once slightly displaced, it moves quickly away from that position.

The third is neutral equilibrium, exemplified by a glass marble on a flat table — when disturbed, it moves but comes to rest wherever the external force stops. It remains in equilibrium without returning to its original position or moving further. In everyday terms, this can be likened to a situation where it's hard for individuals to significantly increase income or completely fall into poverty, but maintaining a basic standard of living is manageable. The fourth is metastable equilibrium. In this state, individuals can recover from small disturbances, but a sufficient deviation would irreversibly lead them to another state.

These concepts can be used to develop a quantitative model for the kill line. Essentially, this framework would address two key questions: whether resilience exists, and in which direction it operates. This means, does a kill line exist if a society is in a state of dynamic equilibrium. After the equilibrium is disrupted, do individuals accelerate into decline toward an unstable equilibrium, or is there a restoring force that enables them to return to a stable equilibrium?

Using this framework, we can take the United States and China as examples. For the US, those living in poverty can be seen as existing in a stable equilibrium at a low level. They have essentially hit the bottom with little room to fall further, and there is no systematic poverty alleviation effort to lift them out. Instead, industries such as processed food, pharmaceuticals and the drug trade exploit this demographic, keeping them in a state of stable equilibrium with low living standards. Meanwhile, the elites or capitalists in the US, facilitated by mechanisms such as the "revolving door", which describes the transition of public officials into lobbyists of industries, are also in a stable equilibrium.

On the other hand, the US middle class, which is the primary target of the kill line, is in a state of unstable equilibrium. The kill line is a critical threshold for this segment of the population. Once it gets breached, there is no force that can return these individuals to stability. Instead, mechanisms exist that accelerate their downward mobility.

In contrast, China's low-income population demonstrates resilience in returning to a stable equilibrium. This is the fundamental difference between the situation in the US and in China.

This resilience is underpinned by the central authorities' commitment to poverty alleviation, the collective ownership of land, and equal access to basic public services. These institutional safeguards create a social safety net, enabling those who fall into poverty to regain stability.

Through its nationwide poverty alleviation campaign, China has successfully lifted its low-income population out of poverty. For China's middle-income group, there is no pronounced mechanism of unstable equilibrium or the kill line. Even if individuals face financial setbacks, they often have alternatives — such as relocating to a smaller county where housing is more affordable — where they can maintain a relatively decent standard of living with their savings. China's institutional framework prevents the emergence of a kill line within its middle-income group.

The author is a research fellow of the Center for International Knowledge on Development. The views don't necessarily represent those of China Daily.

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