Interaction is a kind of action that occurs as two or more objects have an effect upon one another. The idea of a two-way effect is essential in the concept of interaction, as opposed to a one-way causal effect. Closely related terms are interactivity and interconnectivity, of which the latter deals with the interactions of interactions within systems: combinations of many simple interactions can lead to surprising emergent phenomena. Interaction has different tailored meanings in various sciences.
In physics, a fundamental interaction (depending on the nature of the interaction, it might also be called a fundamental force) is a process by which elementary particles interact with each other. An interaction is often described as a physical field, and is mediated by the exchange of gauge bosons between particles. For example, the interaction of charged particles takes place through the mediation of electromagnetic fields, whereas beta decay occurs by means of the weak interaction. An interaction is fundamental when it cannot be described in terms of other interactions. There are four known fundamental interactions in nature: The electromagnetic, strong, weak and gravitational interactions. The weak and electromagnetic interactions are unified in electroweak theory, which could in turn be unified with the strong force in a Grand Unified Theory and further with gravity in a theory of everything, but experimental results are yet to prove this.
Interactions between atoms and molecules:
In medicine, most medications can be safely used with other medicines, but particular combinations of medicines need to be monitored for interactions, often by the pharmacist. Interactions between medications fall generally into one of two main categories:
In terms of efficacy, there can be three types of interactions between medications: additive, synergistic, and antagonistic.
Geneticists work with a number of different genetic interaction modes to characterize how the combination of two mutations affect (or does not affect) the phenotype: noninteractive, synthetic, asynthetic, suppressive, epistatic, conditional, additive, single-nonmonotonic and double-nonmonotonic. Further characterizations is enhancement interaction and nonadditive interaction. Biosemioticists investigate sign-mediated interactions within and between organisms that underlie syntactic, pragmatic and semantic rules.
The word epistasis is also used for genetic interaction in some contexts.
In sociology, social interaction is a dynamic, changing sequence of social actions between individuals (or groups) who modify their actions and reactions due to the actions by their interaction partner(s). Social interactions can be differentiated into accidental, repeated, regular, and regulated. Social interactions form the basis of social relations.
The most common forms of social interaction are exchange, competition, conflict, cooperation, and accommodation.
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