My Trip With Dark Energy 🪐 In 1991: There was no accepted evidence for cosmic acceleration yet. The term “dark energy” wasn’t in use — and the cosmological constant (Λ) was mostly considered unnecessary or even unfashionable . Context: Most cosmologists assumed the universe’s expansion was slowing down , due to gravity from matter (ordinary + dark matter). The two main models debated were: Einstein–de Sitter model: Flat, matter-dominated, Λ = 0. Open CDM model: Λ = 0, but with less matter, implying open curvature. The cosmological constant’s status: Λ was originally added by Einstein (1917) to allow a static universe, then discarded after Hubble’s discovery of expansion. In the 1980s and early 1990s, Λ occasionally resurfaced as a mathematical fix to make models fit galaxy distributions or ages of stars—but it had no physical interpretation . It was seen as a “fudge factor,” not a real component of the cosmos. Observational state (1991): No T...