are celebrated for their reasoned claims that all things change. Early modern speculation about cosmic evolution began more than a century ago, including the broad insights of Robert Chambers, Herbert Spencer, Charles Sanders Peirce, and Lawrence Henderson. Only in the mid-20th century was the cosmic-evolutionary scenario articulated as a research paradigm to include empirical studies of galaxies, stars, planets, and life—in short, an expansive agenda that combines physical, biological, and cultural evolution. Harlow Shapley widely articulated the idea of cosmic evolution (often calling it "cosmography") in public venues at mid-century, and NASA embraced it in the late 20th century as part of its more limited astrobiology program. Carl Sagan, Eric Chaisson, Hubert Reeves, Erich Jantsch, and Preston Cloud, among others, extensively championed cosmic evolution at roughly the same time around 1980. This extremely broad subject now continues to be formulated as both a technical research program and a scientific worldview for the 21st century. One popular collection of scholarly materials on cosmic evolution is based on teaching and research that has been underway at Harvard University since the mid-1970s. Complexity, energy, thresholds Cosmic evolution is a quantitative subject, whereas big history typically is not; this is because cosmic evolution is practiced mostly by natural scientists, while big history by social scholars. These two subjects, closely allied and overlapping, benefit from each other; cosmic evolutionists tend to treat universal history linearly, thus humankind enters their story only at the most very recent times, whereas big historians tend to stress humanity and its many cultural achievements, granting human beings a larger part of their story. One can compare and contrast these different emphases by watching two short movies portraying the Big-Bang-to-humankind narrative, one animating time linearly, and the other capturing time (actually look-back time) logarithmically; in the former, humans enter this 14-minute movie in the last second, while in the latter we appear much earlier—yet both are correct. These different treatments of time over ~14 billion years, each with different emphases on historical content, are further clarified by noting that some cosmic evolutionists divide the whole narrative into three phases and seven epochs: Phases: physical evolution → biological evolution → cultural evolution Epochs: particulate → galactic → stellar → planetary → chemical → biological → cultural This contrasts with the approach used by some big historians who divide the narrative into many more thresholds, as noted in the discussion at the end