etenduseks

Etendue is a concept in thermodynamics and information theory that quantifies the "spread" or "dilution" of energy or information. It was introduced by Roland V. L. Roland in the early 20th century and later developed by others. In thermodynamics, étendue is a measure of the total energy that can be transferred from a system to its surroundings. It is directly related to the concept of entropy, which measures the disorder or randomness of a system. Higher étendue implies a greater potential for energy transfer and thus a greater capacity to do work.

The mathematical definition of étendue relates to the integral of the product of area and solid angle over the surface of a radiating body. For a simple surface, it can be thought of as the product of the area and the maximum solid angle through which radiation can escape. This means that a larger area or a wider cone of emission contributes to a higher étendue. In optical systems, étendue is conserved under ideal conditions, meaning that the product of area and solid angle remains constant as light passes through lenses or mirrors. This conservation principle is fundamental in designing optical instruments, as it sets limits on how much light can be collected and focused.

In information theory, étendue can be seen as a measure of the uncertainty or randomness associated with a probability distribution. A more "spread out" distribution, where probabilities are more evenly distributed across possible outcomes, has a higher étendue, indicating greater uncertainty. This parallels the thermodynamic concept where energy is "spread out" and less concentrated. The concept of étendue provides a unified way to think about the limitations and possibilities of energy and information transfer in various physical and abstract systems.