Jwst and the problem of prematurely-formed massive galaxies: pre-mission predictions, early observations, and the structure of the emerging tension with λcdm

The James Webb Space Telescope, operational from July 2022, was designed to test ΛCDM predictions for first-galaxy formation in the z = 8 to z = 20 window. Within six months, NIRCam imaging from the SMACS 0723, GLASS, and CEERS Early Release programmes returned an unexpected population of luminous galaxy candidates at z ≈ 10-16 with inferred stellar masses of 10^9-10^10 M_⊙ at cosmic times of 300-500 Myr after the Big Bang. The Naidu and colleagues (2022) GLASS-z10/z12 discovery, the Castellano and colleagues (2022) z ≈ 9-15 sample, and the converging Harikane and colleagues (2022) and Donnan and colleagues (2022) UV luminosity function analyses together established that the bright-end number density at z > 10 exceeds pre-JWST Behroozi-Silk (2018) and Behroozi-UniverseMachine (2019) predictions by approximately 0.5-1 order of magnitude. Whether this excess reflects genuine over-formation of massive galaxies, contamination by lower-redshift interlopers, calibration systematics, or a ΛCDM breakdown remained unresolved at the December 2022 boundary of this review. I propose, as the original contribution, the Galaxy Formation Tension Index (GFTI), a normalised composite metric on [0,1] integrating five performance dimensions (observed-topredicted number-density ratio, inferred star formation efficiency, stellar-mass-density ratio, UVbright-fraction at z > 10, cross-survey consistency). Applied to the December 2022 dataset, GFTI returns approximately 0.55 — the “significant tension” tier, well below the 0.75 refutation threshold.