Causality (physics)

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Causality[1][2] describes the relationship between causes and effects, is fundamental to all natural science, especially physics, and has an analog in logic. It is also studied from the perspectives of philosophy, computer science, and statistics.


Basic concepts of cause and effect

Humans have a practical interest in their surroundings, and tend to be resistant to the idea things "just happen." If one or more sheep die, humans will attempt to discover why. Learning what has killed the sheep is an important step in protecting the herd. The question can be phrased as, "What caused the sheep to die?" The answer may be "Because the wolves broke their necks," or "Eating too much clover caused them to bloat." These explanations assume the presence of an agent of some kind. In cases where an obvious cause is not discovered, humans may attribute the events to miracles or to evil supernatural agencies. There is a learned preference for some alternative to saying that something occurred without there being a reason for it. Anything that stands as 'uncaused' may motivate us to understand the salient events in their environment.

When trying to answer questions such as, "Why is the water boiling?" it is tempting to search for a single responsible figure: "Mother lit the gas burner under the tea kettle." However, closer examination shows that the lighting of a flame is not the only feature that must be accounted for. Closer study shows that the ambient air pressure is a controlling factor, the Earth's gravity holding the water in the pot is a controlling factor, the temperature to which the water has been heated is a controlling factor, etc.

Given a situation in which water is already sitting in a tea kettle on top of a gas burner, then someone lighting the gas under the kettle may be perceived as the "cause" of the water's boiling. But in the same situation the water would also boil if the air pressure were sufficiently reduced. In more complicated situations, more factors that influence outcomes may be involved. Underlying the expectations that most people hold in regard to the interactions of these several factors are everyday experiences in which someone succeeds in producing a desired result. "If I turn this key, the motor will start." This may be a true statement, but underlying it is a very complicated set of conditions that must all be in place. So the idea of "cause" tends to focus on foreground events and leave out necessary factors that reside in the background.

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