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Physical law

From Academic Kids

A physical law or a law of nature is a scientific generalization based on empirical observations. Laws of nature are conclusions drawn from, or hypotheses confirmed by scientific experiments. The production of a summary description of nature in the form of such laws is the fundamental aim of science. Laws of nature are distinct from legal code and religious Law, and should not be confused with the concept of natural law.

Contents

Description

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

  • true. By definition, there have never been repeatable contradicting observations.
  • universal. They appear to apply everywhere in the universe. (Davies)
  • simple. They are typically expressed in terms of a single mathematical equation. (Davies)
  • absolute. Nothing in the universe appears to affect them. (Davies)
  • eternal. Unchanged since first discovered (although they may have been shown to be approximations of more accurate laws—see "Laws as approximations" below), they appear to be unchanged since the beginning of the universe. It is thus presumed that they will remain unchanged in the future. (Davies)
  • omnipotent. Everything in the universe apparently must comply with them. (Davies)
  • "omniscient" (loosely speaking). The behavior of everything in the universe is automatically and immediately "known" to the laws. (Davies)
  • generally conservative of quantity. (Feynman)
  • often examples of symmetry. (Feynman)
  • typically theoretically reversible in time (if non-quantum), although time itself is irreversible. (Feynman)

Often, those who understand the mathematics and concepts well enough to understand the essence of the physical laws also feel that they possess an inherent intellectual beauty. Many scientists state that they use their perception of this beauty as a guide in developing hypotheses, since there seems to be a connection between beauty and truth.

Physical laws are distinguished from scientific theories by their simplicity. Scientific theories have many of the same properties as laws, but are generally more complex than laws; they have many component parts, and are more likely to change as the body of available experimental data and analysis develops.

Examples

Main article: List of laws in science. See also: scientific laws named after people

Some of the more famous laws of nature are found in Isaac Newton's theories of (now) classical mechanics, presented in his Principia Mathematica, and Albert Einstein's theory of relativity. Other examples of laws of nature include Boyle's law of gases, conservation laws, Ohm's law, the four laws of thermodynamics, etc.

Laws as approximations

Outside the scientific community, it is often assumed that the laws of nature have been proved beyond a doubt, in the same manner that mathematical theorem can be proven. However, this is not so. It is just that no instances have ever been seen where they are repeatably violated. It is always possible for them to be invalidated by repeatable, contradictory experimental evidence, should any be seen. However, fundamental changes to the laws are unlikely in the extreme, since this would imply a change to the basic structure of the universe, which would almost certainly make it immediately uninhabitable (see fine-tuned universe); If the laws were to change, we wouldn't be here to notice.

Well-established laws have indeed been invalidated in some special cases, but the new formulations created to explain the discrepancies can be said to generalize upon, rather than overthrow, the originals. That is, the invalidated laws have been found to be only close approximations, to which other terms or factors must be added to cover previously unaccounted-for conditions, e.g., very large or very small scales of time or space, enormous speeds or masses, etc. Thus, rather than unchanging knowledge, physical laws are actually better viewed as a series of improving approximations.

A well-known example is that of Newton's law of gravity: while it describes the world accurately for most pertinent observations, such as of the movements of astronomical objects in the solar system, it was found to be inaccurate when applied to extremely large masses or velocities. Einstein's theory of general relativity, however, accurately handles gravitational interactions at those extreme conditions, in addition to the range covered by Newton's law. Newton's formula for gravity is still used in most circumstances, as an easier-to-calculate approximation of gravitational law. A similar relationship exists between Maxwell's equations and the theory of quantum electrodynamics; there are several such cases. This suggests the (unanswered) question of whether there are any ultimately true physical laws, or whether they are all just cases where our sensory and rational apparatus have generated mathematically simple approximations, valid within the range of normal human experience, to unobtainable true formulas.

Necessity, origin, and existence

If the universe were purely chaotic, the existence of life as it is known would be impossible, since organized complexity is a defining characteristic of life. The laws of nature create order in the universe, and result in a generally stable environment that, in accordance with the anthropic principle, is permissive of life, including humanity. However, from whence the laws of nature originate and exist, and why they are of the particular form that they are, is unknown, and in the purview of metaphysics.

It has sometimes been suggested that the laws of nature are not real—that they are entirely inventions of the human mind, attempting to make sense of the universe. This is very strongly argued against by the spectacular efficacy of science—its power to solve otherwise intractable problems, and make accurate predictions—and by the fact that newly-discovered laws have typically suggested the existence of previously unknown or unrealized phenomena, which have then been confirmed to exist.

History, and religious influence

The idea that there are underlying laws in nature dates to prehistoric times, since even the recognition of cause-and-effect relationships is an implicit recognition that there are laws of nature. Progress in identifying laws per se, though, seems to have been hampered by belief in animism, and by the attribution of many effects that do not have readily identifiable causes—such as meteorological and astronomical phenomena—to the actions of gods. Early attempts to formulate laws in material terms were made by ancient philosophers, including Aristotle, but suffered from various misconceptions, such as the assumption that observed effects were due to intrinsic properties of objects, e.g. "heaviness", "lightness", etc.

The formal and precise formulation of what are today recognized as correct statements of the laws of nature did not begin until the 17th century in Europe, with the institution of the use of the scientific method. It has been suggested (for example, see Barrow (1991)) that Judaism and Christianity, with their monotheistic belief in God as Lawgiver, have played an important part in creating an ethos suitable to the initial and continuing discovery of the laws.

Significance, and renown of discoverers

Because of the understanding they permit regarding the nature of our existence, and because of their above-mentioned power for problem-solving and prediction, the discoveries of the laws of nature are considered among the greatest intellectual achievements of humanity. Due to their subtlety, their discovery has typically required extraordinary powers of observation and insight, and their discoverers are typically considered among the best and brightest by others in their fields and, notably in the cases of Newton and Einstein, in the general populace as well.

Other fields

Some mathematical theorems and axioms are referred to as laws. Mathematical expressions are different from physical laws in that they don't have an explicit empirical basis.

Examples of other observed phenomena often described as laws include the Titius-Bode law of planetary positions, Zipf's law of linguistics, Moore's law of technological growth. Many of these laws fall within the scope of uncomfortable science. Other laws are pragmatic and observational, such as the law of unintended consequences. By analogy, principles in other fields of study are sometimes loosely referred to as "laws". These include Occam's razor as a principle of philosophy and the Pareto principle of economics.

See also

References

External links

et:Loodusseadus es:Ley cientfica is:Elisfrilgml ja:物理法則 zh:物理定律

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