Homogeneity and heterogeneity

Etymology and spelling

The words homogeneous and heterogeneous come from Medieval Latin homogeneus and heterogeneus, from Ancient Greek ὁμογενής (homogenēs) and ἑτερογενής (heterogenēs), from ὁμός (homos, “same”) and ἕτερος (heteros, “other, another, different”) respectively, followed by γένος (genos, “kind”); -ous is an adjectival suffix.

The alternate spellings "homogenous" and "heterogenous" are commonly, but incorrectly, used. The word "homogenous" strictly speaking is a biological term which has largely been replaced by "homologous", though its use to mean "homogeneous" has seen a rise, since 2000, which makes it an "established variant". "Heterogenous" meanwhile is a term primarily confined to pathology which refers to the property of an object in the body having its origin outside the body.

Scaling

The concepts are the same to every level of complexity, from atoms to populations of animals or people, and galaxies. Hence, an element may be homogeneous on a larger scale, compared to being heterogeneous on a smaller scale. This is known as an effective medium approach, or effective medium approximations.

Examples

Various disciplines understand heterogeneity, or being heterogeneous, in different ways. For example:

Chemistry

In chemistry, a heterogeneous mixture consists of either or both of a) multiple states of matter or b) hydrophilic and hydrophobic substances in one mixture; an example of the latter would be a mixture of water, octane, and silicone grease. Heterogeneous solids, liquids, and gases may be made homogeneous by melting, stirring, or by allowing time to pass for diffusion to distribute the molecules evenly. For example, adding dye to water will create a heterogeneous solution at first, but will become homogeneous over time. Entropy allows for heterogeneous substances to become homogeneous over time.

A heterogeneous mixture is a mixture of two or more compounds. Examples are: mixtures of sand and water or sand and iron filings, a conglomerate rock, water and oil, a salad, trail mix, and concrete (not cement). A mixture can be determined to be homogeneous when everything is settled and equal, and the liquid, gas, object is one color or the same form. Various models have been proposed to model the concentrations in different phases. The phenomena to be considered are mass rates and reaction.

Homogeneous and heterogeneous reactions

Homogeneous reactions are chemical reactions in which the reactants and products are in the same phase, while heterogeneous reactions have reactants in two or more phases. Reactions that take place on the surface of a catalyst of a different phase are also heterogeneous. A reaction between two gases or two miscible liquids is homogeneous. A reaction between a gas and a liquid, a gas and a solid or a liquid and a solid is heterogeneous.

Geology

Earth is a heterogeneous substance in many aspects. e.g. rocks (geology) are inherently heterogeneous, usually occurring at the micro-scale and mini-scale.

Information technology

With information technology, heterogeneous computing occurs in a network comprising different types of computers, potentially with vastly differing memory sizes, processing power and even basic underlying architecture.

Mathematics and statistics

In algebra, homogeneous polynomials have the same number of factors of a given kind.

In statistical meta-analysis, study heterogeneity is when multiple studies on an effect are actually measuring somewhat different effects due to differences in subject population, intervention, choice of analysis, experimental design, etc.; this can cause problems in attempts to summarize the meaning of the studies.

Medicine

In medicine and genetics, a genetic or allelic heterogeneous condition is one where the same disease or condition can be caused, or contributed to, by several factors. In the case of genetics, varying different genes or alleles.

In cancer research, cancer cell heterogeneity is thought to be one of the underlying reasons that make treatment of cancer difficult.

Physics

In physics, "heterogeneous" is understood to mean "having physical properties that vary within the medium".

Sociology

In sociology, "heterogeneous" may refer to a society or group that includes individuals of differing ethnicities, cultural backgrounds, sexes, or ages.