Hysteresis is a concept referring to situations where the effects of a system persist even after the initial causes have been removed. This phenomenon is prevalent in various fields such as physics, engineering, and economics. In essence, hysteresis implies a sort of “lag” or delayed response in a system, leading to residual effects that continue to influence the system’s behavior even after external forces have ceased.
Hysteresis in Economics
Unemployment
In economics, hysteresis frequently relates to the labor market, particularly in discussions of unemployment. When an economy experiences prolonged periods of high unemployment, the workforce may undergo skill degradation and loss of work habits, making it difficult for employment levels to bounce back quickly even after economic conditions improve. This can be illustrated by the following simple economic formula:
where \(U_t\) is the unemployment rate at time \(t\), \(U_e\) is the equilibrium unemployment rate, and \(\phi\) represents the degree of hysteresis.
Example
A classic example of hysteresis in unemployment is the Eurozone crisis, where some countries experienced high levels of structural unemployment that did not return to pre-crisis levels even after economic recovery.
Hysteresis in Physics and Engineering
Magnetic Hysteresis
In physics, hysteresis is often discussed in the context of magnetism. When a magnetic material like iron is magnetized by an external magnetic field, it retains some magnetization even after the external field is removed. This residual magnetization is an example of hysteresis in magnetic systems.
Stress-Strain Relations
In engineering, hysteresis can describe the relationship between stress and strain in materials. For instance, when a material is subjected to cyclic loading and unloading, it may exhibit a different strain path during loading and unloading phases, indicated by a hysteresis loop on the stress-strain curve.
Historical Context
The term hysteresis comes from the Greek word “ὑστέρησις” (hysterēsis), meaning “deficiency” or “lagging behind.” It was first introduced in 1890 by Sir James Alfred Ewing to describe the lag between magnetic flux density and magnetic field strength in magnetic materials.
Applicability
Hysteresis is applicable in multiple domains:
- Economics: Persistent unemployment, inflation inertia
- Physics: Magnetic materials, superconductivity
- Engineering: Material fatigue, systems control
Comparisons and Related Terms
Path Dependence
Path dependence refers to the historical dependency in a process, where the outcome is heavily influenced by the initial conditions, not dissimilar to hysteresis but often without the focus on residual effects after causative factors are removed.
Memory Effect
Memory effect describes situations where past states affect the current behavior of a system, akin to hysteresis but more contextualized within specific scenarios like battery charge cycles or shape-memory alloys.
FAQs
What are common fields where hysteresis is observed?
How does hysteresis affect economic policies?
Can hysteresis be beneficial?
References
- Blanchard, O. J., & Summers, L. H. (1986). Hysteresis and the European unemployment problem. NBER Macroeconomics Annual, 1, 15-78.
- Bertotti, G. (1998). Hysteresis in Magnetism: For Physicists, Materials Scientists, and Engineers. Academic Press.
Summary
In summary, hysteresis is a fundamental concept applicable across various domains. It explains why systems exhibit residual effects long after initial causes are removed, from unemployment in economics to magnetic properties in physics. The understanding of hysteresis allows for more effective interventions, better material performance, and a deeper comprehension of dynamic systems.
