  It was recently proposed that five-dimensional inflation can relate the
causal size of the observable universe to the present weakness of gravitational
interactions by blowing up an extra compact dimension from the microscopic
fundamental length of gravity to a large size in the micron range, as required
in the Dark Dimension proposal. Here, we compute the power spectrum of all
primordial fluctuations emerging from a 5-dimensional inflaton in a slow-roll
region of its potential, showing an interesting change of behaviour at large
scales corresponding to angles larger than about 10 degrees in the sky.
