Surface brightness fluctuations turn the graininess of galaxy images into distances, and the method delivered one of the Hubble tension's cleanest independent votes. An elliptical galaxy's image is statistically grainy because each pixel samples a finite number of stars; nearer galaxies look grainier, more distant ones smoother, and the effect calibrates into a precision distance indicator reaching well past 100 megaparsecs, with systematics, stellar population corrections, dust masking, point-source removal, entirely unlike the Cepheid-supernova chain's. The definitive application (Blakeslee et al. 2021: 63 ellipticals to 100 Mpc with HST) yielded H0 = 73.3 +/- 0.7 (stat) +/- 2.4 (sys) km/s/Mpc, landing precisely on the SH0ES value through an almost completely independent route, and JWST-era SBF programs are extending the reach and tightening the infrared calibration.
The method's testimony compounds the tension's central mystery: by now the high camp includes Cepheid-supernova ladders, TRGB recalibrations, masers, time delays, Tully-Fisher, and SBF, methods sharing essentially no systematics, all anchored in or sampling the local few hundred megaparsecs, all landing between 73 and 76; while the low camp, CMB, BAO with CMB-calibrated rulers, chronometers, samples the early universe or the broad volume and lands at 67 to 69. The standard framing demands one of these families be collectively, coherently wrong, with errors that conspire across unrelated physics; a quarter century of auditing has produced no such conspiracy.
The standing is corroboration fatigue: each new independent local method that lands high makes the collective-error hypothesis less tenable, and SBF's JWST extension toward 300 megaparsecs will probe whether the high values persist to the volume's edge or begin the descent the gradient interpretations predict.