Thread drift can be rather magical, and among the commenters here it frequently is. Thus the last discussion thread revisiting space fighters also touched, just lightly, on the special magic of time, with commenter ushumgal tossing a pebble 40,000 years into the future and wondering what the ripples would be like.
What can we say about the world(s) of the year 42,010? We can guess, with fair confidence, that there won't be militaries that speak in acronyms and wear uniforms with shoulderboards and chest salad. The languages they use will surely not be comprehensible to us, even if derived from English.
As ushumgal points out, even the food they eat may be unrecognizable, quite apart from fancy genetic engineering and the like. Most of our domestic animals and plants are already far removed from their ancestral forms domesticated just a few thousand years ago. In the case of corn (maize, to some of you), Mesoamericans worked it over so thoroughly that its wild progenitor remains uncertain.
For that matter, our descendents could well be unrecognizable: supplanted by our creations, or uploaded into some data cloud, or at least gene modded to a fare thee well. For this discussion I'll set aside transhumanism, because I don't see how it can be discussed in any but the vaguest terms. I'm a bit doubtful that we would choose that path in any case, because most of our joys (and sorrows) - as well as such minor pleasures as a good meal - are part of our inheritance from the primate house, and not things we will wish to relinquish.
So let us merely roll 40,000 years around in our heads, considered as a historical time scale.(Disclaimer: I've heard of Warhammer 40K, of course, but don't know the first thing about it.) The same temporal distance in the other direction takes us to the Upper Paleolithic, and the earliest people to leave tangible markers of their humanity. The first spoken sentence, and perhaps the first song, may at a guess date back two or three times as far, but we have no direct way to judge.
The span of recorded history is much shorter. I have not been able to determine what is the first attested historical event, or when, but the record seems to trail off a bit less than 5000 years ago. Thus we are looking at a period some eight times longer; to people of the year 40,000, we stand very near the Dawn of History. A catastrophic dark age or two, or perhaps just a really bad disk crash, could retrospectively wipe us out, or at least leave archeologists scratching their heads over the site of the British Museum.
Even if the record is fully preserved they mostly won't spend much time thinking about us. Perception of the past tends to be logarithmic. A fair amount of third millennium BCE history is known, but about all we generally remember is the Pyramids. They might remember our own era, perhaps as the beginning of space travel. Or it may all blur together: pyramids, gunpowder, and the first interstellar colony, all roughly contemporary developments at the start of recorded history.
On the other hand, the past is in some ways foreshortened. The history of reflective thought goes back some 2500 years, half the length of recorded history. We still engage intellectually with Confucius and Plato, and morally with the Buddha and the prophetic books of the Hebrew scripture. In this rather sanguinary group we examine the battles of Alexander, and the strategies of Sun Tzu.
Even on the level of popular soap opera we still rubberneck at the Julio-Claudian train wreck, and its Bollywood and Hong Kong counterparts. What is the sell-by date for Nero and Messalina? They may remain vivid, while (say) the whole period from 15,000 to 30,000 falls into the memory hole, too far back to feel relevant and not colorful enough to muscle aside Rome or the Three Kingdoms.
So ... how do you fill 40,000 years of history? And when at last you reach the future present, what do you serve for dinner? Discuss.
Related posts: Last year I reviewed Psychohistorical Crisis, by Donald Kingsbury, which among other things considers the challenges of remembering a long historical past. And in the Tough Guide to the Known Galaxy I dealt with really long time periods.
Image note: The Lascaux cave paintings are a mere 16,000 years old, or thereabouts.