Based on entropy considerations and the arrow of time Penrose argued that the
universe must have started in a special initial singularity with vanishing Weyl
curvature. This is often interpreted to be at odds with inflation. Here we
argue just the opposite, that Penrose’s persuasions are in fact consistent with
inflation. Using the example of power law inflation, we show that inflation
begins with a past null singularity, where Weyl tensor vanishes when the metric
is initially exactly conformally flat. This initial state precisely obeys
Penrose’s conditions. The initial null singularity breaks $T$-reversal
spontaneously and picks the arrow of time. It can be regulated and interpreted
as a creation of a universe from nothing, initially fitting in a bubble of
Planckian size when it materializes. Penrose’s initial conditions are favored
by the initial $O(4)$ symmetry of the bubble, selected by extremality of the
regulated Euclidean action. The predicted observables are marginally in tension
with the data, but they can fit if small corrections to power law inflation
kick in during the last 60 efolds.
