James Webb Is Finding Galaxies That Shouldn't Exist. Cosmologists Are Quietly Alarmed.
The standard model of cosmic evolution predicts what the early universe should look like. Webb is finding something different — and the gap between prediction and observation is widening.
The James Webb Space Telescope was designed to see further back in time than any instrument before it — to observe the universe as it was less than 400 million years after the Big Bang, when the first galaxies were just beginning to form. What it has found has created a quiet crisis in cosmology.
The standard model of cosmic evolution — Lambda-CDM, the cosmological constant plus cold dark matter — makes specific predictions about what the early universe should look like. Galaxies in the first billion years should be small, irregular, and relatively dim. They should not yet have had time to accumulate the mass or develop the structure of mature galaxies.
Webb is finding galaxies that are too big, too bright, and too structured to exist at the distances — and therefore the ages — at which they are being observed. Some of these objects contain as much stellar mass as the Milky Way, which took over 13 billion years to accumulate, yet they appear to have formed within the first 700 million years of the universe's existence.
The initial response from the cosmological community was cautious: measurement error, calibration issues, misidentified redshifts. As more data has accumulated, those explanations have become harder to sustain. The objects are real. They are where Webb says they are. They are as massive as the measurements suggest.
The implications are significant. Either the standard model is missing something fundamental about how galaxies form — which would require revisions to our understanding of dark matter, dark energy, or both — or the objects are being misinterpreted in some systematic way that nobody has yet identified. Neither option is comfortable.
Cosmology has been here before. Anomalies that don't fit the model have a history of either resolving into confirmation of the model or forcing revisions that turn out to be more interesting than the original theory. Which of those this turns out to be is one of the more compelling open questions in science right now.