Sustainable development theory has come from the field of ecological economics. According to this theory, sustainable development involves achieving objectives in three realms: ecological, economic and social. The ecological objective is maintaining a sustainable scale of energy and material flows through the environment such that carrying capacity of the biosphere is not affected. The economic objective seeks to provide an efficient allocation of resources in conformity with consumer preferences and the ability to pay. The social objective aims at a just distribution of resources among the public, including future generations. The overall objective of a sustainable society is the achievement of sustainability in economic, ecological and social systems.