Abstract The Integrated Sachs-Wolfe (ISW) effect, the net energy gain or loss of cosmic microwave background photons traversing time-varying large-scale gravitational potential wells, is cited by the standard Lambda-CDM model as independent evidence for dark energy. In that framework, the ISW signal arises because accelerated expansion caused by dark energy causes gravitational potentials to decay as photons cross them, producing a correlation between CMB temperature fluctuations and the locations of large-scale structure tracers such as supervoids and superclusters. This paper re-examines the ISW effect from within the Big Flare-Up Theory framework. The BFUT reinterpretation is as follows. In a living, infinite, non-expanding universe maintained in dynamic thermal equilibrium through the Spaticle field, CMB temperature is not a relic but a present-moment equilibrium state of the substrate itself. The local temperature of the Spaticle field is not perfectly uniform; it responds to local matter density, gravitational potential depth, and energy input from embedded sources. In regions of high matter concentration such as superclusters, the local Spaticle field is marginally warmer; in supervoids it is marginally cooler. The observed CMB temperature correlation with large-scale structure is therefore a direct measurement of present-moment Spaticle field temperature variations tracking the matter density field - not a record of photons gaining or losing energy by traversing decaying gravitational potential wells. This paper further demonstrates that the ISW evidence for dark energy is substantially weaker than its prominence suggests. The cross-correlation detection is typically at 3 to 4 sigma, making it the least statistically secure of all the major Lambda-CDM pillars. More critically, the stacked ISW signal from supervoids and superclusters - the most direct observational form of the effect - is consistently 4 to 10 times larger than Lambda-CDM's own predictions, a discrepancy that has persisted across independent surveys using SDSS, BOSS, DES, and eBOSS data for over fifteen years. Lambda-CDM's own framework cannot accommodate its own claimed evidence. BFUT, by contrast, predicts environment-correlated Spaticle field temperature variations without requiring dark energy, without requiring an expanding
Vijay Shankar Sharma (Sun,) studied this question.