tl;dr - You reminded me of a favorite article on relativism and understanding other cultures (especially other cultures very far from us in time and circumstances). There's a quote from the piece below, and I highly recommend it to anyone interested in this issue.
>> As some people say, we're already in a Singularity relative to ancient Grecians, inasmuch as they couldn't understand our world at all... and I think it's true in the opposite direction, too.
This reminded me immediately of a line of thought from Bernard Williams[1]. He's discussing relativism, and he argues that there is some truth to it (roughly: relativism, understood in a very specific way makes sense for ethics, but not for science). In order to make this argument, he considers what it would mean for two or more systems of belief to come into contact. (As a shorthand, he calls a system of belief an S throughout the paper.) He wants to make the claim that relativism is coherent in cases where Ss can to some extent understand one another, but there is no real possibility of a person with S1 giving that up in favor of S2 (or vice-versa).
This is already very long, but my point is that I think it's not so much that "they couldn't understand our world at all" or that we can't understand theirs. It's rather that however well we understand it, we simply could not give up our S and take up theirs - not without massive false consciousness.
Here's the key quote you made me think of:
>> [M]any Ss which have been held are not real options now. The life of a Greek Bronze Age chief, or a mediaeval Samurai, and the outlooks that go with those, are not real options for us: there is no way of living them. This is not to say that reflection on those value-systems may not provide inspiration for thoughts about elements missing from modern life, but there is no way of taking on those Ss. Even Utopian projects among a small band of enthusiasts could not reproduce that life: still more, the project of re-enacting it on a societal scale in the context of actual modern industrial life would involve one of those social or political mistakes, in fact a vast illusion. The prospect of removing the conditions of modern industrial life altogether is something else again -- another, though different, impossibility.[2]
[1] http://en.wikipedia.org/wiki/Bernard_Williams
[2] "The Truth in Relativsm" Proceedings of the Aristotelian Society, New Series, Vol. 75, (1974 - 1975), pp. 215-228, on page 224. It's here on JSTOR, in case people have access to that: http://www.jstor.org/stable/view/4544875. It's also collected in Bernard Williams Moral Luck.