Ever since it opened its giant infrared eye on the cosmos after its December 2021 launch, the James Webb Space Telescope (JWST) has found a shocking surfeit of bright galaxies that stretch back to the very early universe. Their brightness—a proxy for their numbers of stars and hence their mass—is deeply puzzling because galaxies shouldn’t have had enough time to become so bulky in such early cosmic epochs. Imagine visiting a foreign land and finding that many of its toddlers weighed as much as teenagers. You might have questions, too: Is the cause of such large children something in the water, or might it instead be that your grasp of human growth is fundamentally flawed? Theorists who pondered JWST’s big, bright early galaxies felt much the same: Was something fundamental amiss in our understanding of cosmology? Namely, was our knowledge of the expansion of the universe following the big bang simply wrong?
The answer, it appears, need not be quite so dramatic.
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