  Science in the 21st century seems to be governed by novel approaches
involving interdisciplinary work, systemic perspectives and complexity theory
concepts. These new paradigms force us to leave aside our elder mechanistic
approaches and embrace new starting points based on stochasticity, chaoticity,
statistics and probability. In this work we review the fundamental ideas of
complexity theory and the classic probabilistic models to study complex
systems, based on the law of large numbers, central limit theorems and stable
distributions. We also talk about power laws as the most common model for
phenomena showing long tail distributions and we explore the principal
difficulties that arise in practice with this kind of models. We show a novel
alternative for the descripition of this type of phenomena and lastly we show
two examples that illustrate the applications of this new model.
