Physical law

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A physical law or scientific law is a scientific generalization based on empirical observations of physical behaviour (i.e. the law of nature [1]). Laws of nature are observable. Scientific laws are empirical, describing observable patterns. Empirical laws are typically conclusions based on repeated scientific experiments and simple observations, over many years, and which have become accepted universally within the scientific community. The production of a summary description of our environment in the form of such laws is a fundamental aim of science. These terms are not used the same way by all authors. Some philosophers e.g. Norman Swartz use "physical law" to mean what others mean by "natural law"/"law of nature".[2]

Laws of nature are distinct from religious and civil law, and should not be confused with the concept of natural law. Nor should 'physical law' be confused with 'law of physics' - the term 'physical law' usually covers laws in other sciences (e.g. biology) as well.



Several general properties of physical laws have been identified (see Davies (1992) and Feynman (1965) as noted, although each of the characterizations are not necessarily original to them). Physical laws are:

  • True, at least within their regime of validity. By definition, there have never been repeatable contradicting observations.
  • Universal. They appear to apply everywhere in the universe. (Davies, 1992:82)
  • Simple. They are typically expressed in terms of a single mathematical equation. (Davies)
  • Absolute. Nothing in the universe appears to affect them. (Davies, 1992:82)
  • Stable. Unchanged since first discovered (although they may have been shown to be approximations of more accurate laws—see "Laws as approximations" below),
  • Omnipotent. Everything in the universe apparently must comply with them (according to observations). (Davies, 1992:83)
  • Generally conservative of quantity. (Feynman, 1965:59)
  • Often expressions of existing homogeneities (symmetries) of space and time. (Feynman)
  • Typically theoretically reversible in time (if non-quantum), although time itself is irreversible. (Feynman)

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