Hey there, i have a question regarding basic inflation and structure formation via linear first order perturbation theory in cosmology. I read through different material (Baumann lecture notes, wikipedia articles, Mukhanov, ...), but at this point i am just confused and find it hard to get an overall picture. My basic questions are: What happened when? When were the perturbations created? when did they leave the horizon and when did they reenter the horizon? On the other hand, i feel like i am still missing a lot more. Out of my head, the thing would look like this (its not even a timeline, just a order): 1) Big Bang Singularity 2) Oscillating primordial quantum fluctuations 3) Inflation Starts 4) Fluctuations get stretched to the size of the observable universe (thereby creating homogeneity?) 5) Fluctuations leave horizon and freeze 6) Inflation Ends 7) Radiation dominated phase 8) Fluctuations reenter horizon (and destroy homogeneity?) and create large scale structure of the universe 9) Photon Decoupling/CMB 10) Matter Dominated phase 11) Dark Matter Dominated phase ...But, i dont feel like i fully understand it nor do i know if its right or wrong. Like, the perturbations have to reenter before the Photon decoupling, because otherwise they would not be visible in the CMB spectrum, right? Wouldnt they start to oscillate again once theyre back in the horizon? What effect would that have? It would be very nice if any of you could help me get the picture right :) Thanks! PS: Sorry, at first i created this thread in the GR section yesterday, but now just realized theres actually a Cosmology section as well.