It's jarring to think that if intelligent life were on Kepler 452-b and observing Earth, we're so far away that they would be seeing our "civilizations" in 615 AD: shrinking global population as the old Roman and Byzantine empires are overrun by barbarian hordes and Arab conquest, with some pockets of human progress in China.

Is there something uncivilized about the Arab conquest of Byzantine lands? Had the Kepler 452-b-ians been observing Earthians but a few hundred years prior, they'd have seen the Romans doing much the same to expand their own empire. And the Arabs did quite a good job to not only preserve the Roman intellectual and scientific state of the art, but to contribute their own advancements of those fields.

we're so far away that they would be seeing our "civilizations" in 615 AD: shrinking global population as the old Roman and Byzantine empires are overrun by barbarian hordes and Arab conquest, with some pockets of human progress in China.

Err, the Byzantine empire was still going strong for 6 centuries after that (and still existed, but not in a good shape, for 8).

It never got overrun by "barbarian hordes", but it did have a run in with thieving "supposedely christian horders" on their way to the Crusades in the 12th century, and was finally overrun by the muslim Ottoman empire in the 14th century.