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Formation of structures such as galaxies and galaxy clusters require anisotropies in the cosmic plasma which (as I understand) were due to the anisotropies or density inhomogeneities created by Baryon acoustic oscillations (BAO). Here is a very nice short video. But I also hear that inflation played a role in structure formation. How are these two factors related?

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Inflation sowed the seeds of structure formation by amplifying quantum fluctuations. After inflation ended and the universe reheated, the fluctuations were manifested as density perturbations in the primordial plasma. As gravity acted on these overdensities, compressing them, radiation pressure acted as a restoring force, rarefying them. The result was a spectrum of acoustic oscillations across a wide range of scales. The signature of these oscillations - hot plasma at compression and cold at rarefaction - is seen as temperature anisotropies across the CMB sky and baryon acoustic oscillations in structure surveys.

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  • $\begingroup$ What do you mean by "...universe reheated"?@bapowell $\endgroup$ – SRS Apr 11 at 5:01

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