After evidence was obtained in the 1920s that the universe is expanding, it became reasonable to ask: Will the universe continue to expand indefinitely, or is there enough mass in it for the mutual attraction of its constituents to bring this expansion to a halt? It can be calculated that the critical density of matter needed to brake the expansion and "close" the universe is equivalent to three hydrogen atoms per cubic meter. But the density of the observable universe-luminous matter in the form of galaxies-comes to only a fraction of this. If the expansion of the universe is to stop, there must be enough invisible matter in the universe to exceed the luminous matter in density by a factor of roughly 70.

Our contribution to the search for this "missing matter" has been to study the rotational velocity of galaxies at various distances from their center of rotation. It has been known for some time that outside the bright nucleus of a typical spiral galaxy luminosity falls off rapidly with distance from the center. If luminosity were a true indicator of mass, most of the mass would be concentrated toward the center. Outside the nucleus the rotational velocity would decrease geometrically with distance from the center, in conformity with Kepler's law. Instead we have found that the rotational velocity in spiral galaxies either remains constant with increasing distance from the center or increases slightly. This unexpected result indicates that the falloff in luminous mass with distance from the center is balanced by an increase in nonluminous mass.

Our findings suggest that as much as 90 percent of the mass of the universe is not radiating at any wavelength with enough intensity to be detected on the Earth. Such dark matter could be in the form of extremely dim stars of low mass, of large planets like Jupiter, or of black holes, either small or massive. While it has not yet been determined whether this mass is sufficient to close the universe, some physicists consider it significant that estimates are converging on the critical value.

    Many researchers regard Thailand's recent economic growth, as reflected by its gross domestic product (GDP) growth rates, as an example of the success of a modern technological development strategy based on the market economics of industrialized countries. Yet by focusing solely on aggregate economic growth data as the measure of Thailand's development, these researchers have overlooked the economic impact of rural development projects that improve people's daily lives at the village levelsuch as the cooperative raising of water buffalo, improved sanitation, and the development of food crops both for consumption and for sale at local markets; such projects are not adequately reflected in the country's GDP. These researchers, influenced by Robert Heilbroner's now outdated development theory, tend to view nontechnological development as an obstacle to progress. Heilbroner's theory has become doctrine in some economics textbooks: for example, Monte Palmer disparages nontechnological rural development projects as inhibiting constructive change. Yet as Ann Kelleher's two recent case studies of the Thai villages Non Muang and Dong Keng illustrate, the nontechnological-versus-technological dichotomy can lead researchers not only to overlook real advances achieved by rural development projects but also mistakenly to conclude that because such advances are initiated by rural leaders and are based on traditional values and practices, they retard "real" economic development.