lifetimes

Lifetimes refer to the duration of existence or validity of something. The term is used across disciplines to describe how long an entity lasts from its beginning to its end or to the point at which it can no longer function or be used.

Biology and medicine focus on lifespan: lifespan is the length of an organism's life under normal conditions; life expectancy is a statistical measure of the average duration of life for a population. Species display a wide range of maximum lifespans, influenced by genetics, metabolism, reproduction, and environment. Humans have seen substantial increases in life expectancy over the last century due to public health, though maximum lifespans remain around a few hundred years at most. Lifespan studies compare organisms, aging mechanisms, and age-related diseases.

Ecology and conservation also consider lifetimes of individuals within populations, as well as generational turnover and ecosystem dynamics.

In computing and information technology, lifetime describes how long a resource or reference remains valid. In programming languages with strict memory safety, such as Rust, lifetimes are annotations that help ensure references do not outlive the data they point to. In other contexts, the term also describes shelf life or the usable period of products, batteries, or chemical agents, after which performance degrades.

Understanding lifetimes helps in planning, reliability, and policy, from biology and medicine to engineering and information systems.