Today's widely used economic theories have greatly contributed to the economic, social and environmental crisis. Those theories justified a society which supports inequality and accepts the destruction of the environment. In my lecture I will first describe why and how that happened. However, the main question for a sustainable world is this: is there another way? According to many researchers, yes, another way is possible, and to point the way to a different understanding and description of economic reality, in the lecture I will present a sketch of just such a mathematical description of economic processes, which considers the needs of sustainable development and agrees with experimental observations in the social sciences. This mathematical description was created without using customary but obviously false approaches such as optimisation, equilibrium and the assumption that individuals have complete knowledge of the whole world. After a short look at the mathematical basis, the results, effects and predictions of the various theories are compared and it is shown how the presented theory contributes to a more accurate description of reality and to building a sustainable world.