Before multiverses, inflation had a day job: explain why space is so flat and so uniform on large scales.
Geometry of space looks extremely close to “flat.” Without a mechanism, that requires absurd fine-tuning of early conditions.
Opposite sides of the sky are nearly the same temperature, yet in a simple Big Bang they never had time to talk. How did they agree?
A brief era of exponential expansion — inflation — stretches a tiny, already-smoothed region to cosmic size. Flatness and uniformity stop looking miraculous; they look like what expansion does.
Same toolkit later opens the multiverse door. That’s the whole hinge of this series.
What was inflation originally trying to solve? (tap one)