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Why cannot telescopes use light to observe the universe before recombination?

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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.

Telescopes cannot use light to observe the universe before the period of recombination because the early universe was essentially opaque to electromagnetic radiation.12

Before recombination, the universe was filled with a hot, dense plasma consisting of ionized atoms and free electrons. In this state, photons constantly interacted with these charged particles through scattering, preventing light from traveling freely through space. Because the universe was opaque, light could not escape to reach our telescopes, effectively creating a barrier to direct observation.123

It was only when the universe cooled sufficiently—at a redshift of about 1,090—that electrons and nuclei combined to form neutral atoms, a process known as recombination. At this "decoupling time," the universe suddenly became transparent, allowing light to travel unimpeded. The cosmic microwave background represents this first light that was finally able to stream through the universe.142