Over nearly fifty years, Big History has evolved as an interdisciplinary approach, connecting cosmic, geological, biological, and cultural phenomena into a unified narrative of increasing complexity. This paper critically examines various theoretical frameworks within Big History, focusing on their scientific soundness. While progress has been made, challenges persist in establishing a theoretical core and achieving consensus. Commonalities exist, such as the recognition of a trend toward increasing complexity, the division into temporal eras and periods, and the acknowledgment of unique dynamics defining these phases. However, a consensus on the best foundational principles and canonical periods remains elusive. The paper suggests three strategies for theory development: employing cross-disciplinary theories, generalizing discipline-specific theories, or inventing novel theories. Each approach requires further refinement and empirical testing to contribute to consensus building. Big History is argued to have utility based on its ability to contextualize events within a broader framework, but more ambitious rationales and empirical work may be necessary for skeptical audiences. Despite ongoing theoretical debates, immediate progress can be achieved through empirical endeavors, contributing to the discipline's reputation.