I have been learning about baryon acoustic oscillations. I am however confused about the size of the features as seen on the CMB.
It is claimed that the largest structures have a size given by the distance sound waves could have traveled through the baryon-photon gas by the time of recombination. This is the integral of the speed of sound over time.
Alternatively, as I have been picturing it, if we have an infinite gravitational well that is flat at the bottom, then we have the particle in a box potential from quantum mechanics. Here the sound waves can only travel at most the size of the box. Allowing the potential well to be finite and smoothly curved can only smoothly deform the harmonic solutions of the infinite well. Thus the scale is still set by the size of the well and not the distance sound can travel in free space.
So how are these two ideas compatible?