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What did WMAP measurements show about dark matter in the early universe?

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Oval map of the cosmic microwave background radiation from NASA's WMAP mission, showing a mottled pattern of blue, green, yellow, and red representing temperature variations. — Cosmic microwave background A full-sky map produced by the Wilkinson Microwave Anisotropy Probe (WMAP) showing cosmic background radiation, a very uniform glow of microwaves emitted by the infant universe more than 13 billion years ago. Color differences indicate tiny fluctuations in the intensity of the radiation, a result of tiny variations in the density of matter in the early universe. According to inflation theory, these irregularities were the “seeds” that became the galaxies. WMAP's data support the big bang and inflation models, and cosmic microwave background is at the farthest limits of the observable universe.

Measurements from the Wilkinson Microwave Anisotropy Probe (WMAP) provided critical insights into the composition of the early universe. By mapping irregularities in the cosmic microwave background, WMAP determined that approximately 380,000 years after the big bang, the universe consisted of 63 percent dark matter, 12 percent atoms, 15 percent photons, and 10 percent neutrinos.12

These findings highlighted the significant role dark matter played in the early, dense universe, serving as the foundation for the density variations that eventually allowed matter to coalesce into the stars and galaxies observed today. As the universe expanded, the relative proportions of these components shifted, with dark matter currently accounting for approximately 23 percent of the universe's content.12