Why do you believe it would be lost? Did we lose a substantial amount of previously developed knowledge when the Greek or Roman civilizations collapsed? I humbly suggest that we did not ....
For the peoples living in the decline and aftermath of those collapses, yes they absolutely lost a lot of knowledge. What was common knowledge or specialized in different trades was replaced with ignorance. They didn't know how to farm in the same way or manufacture the same goods, they didn't understand the principles behind the infrastructure that was now crumbling around them, etc. They lacked the engine of broadly perpetuating knowledge we call civilization. Sure, there were individuals in certain places that possessed a fair amount of knowledge, but that knowledge was not widely distributed, and thus it was fragile.
For those collapsed civilizations, it was only that there were sufficient remaining resources in the earth and that their civilization was geographically limited that after centuries and many injections of knowledge from elsewhere that they were able to slowly bounce back, to rediscover what they lost.
The risk today is that we're so interconnected, we've extracted so much of earth's resources, and we've set ourselves on a path towards permanent environmental change, that we may not get another chance at civilization. It may be we recede back to ignorance permanently.
1) the amount of valuable resources sitting above ground is now immense. What's currently missing is a good way to "harvest" them. Necessity being the mother of invention ...
2) Problems with "sufficient remaining resources" are only really relevant if population levels do not decline dramatically. It seems likely to me the civilizational collapse in our era would also be accompanied by substantial population declines, some through the death of the living, some through reduced life expectancy of newly born people, some through reduced birth rates.
3) In the long run, it doesn't matter if individuals lose knowledge, only if the knowledge becomes lost to all and needs to be discovered anew (from the world, rather than from some sort of cultural artifact).
> Did we lose a substantial amount of previously developed knowledge when the Greek or Roman civilizations collapsed?
We lost an enormous amount of knowledge in those time frames.
It took six hundred years for the Romans to reach the same technical level as the Athenians. It then took almost one thousand years for the Italians to again reach the same level as the Romans (this time being greatly increased by the shenanigans of Catholic church).
That was the whole point of the rediscovery of "classical" knowledge from the "ancients" in the Renaissance.
> It took six hundred years for the Romans to reach the same technical level as the Athenians.
When we speak of Ancient Greek technical innovations, we're usually talking about the Hellenism era. That was after Athens had begun to wane as a major intellectual center, and much closer in time to the Romans' ascent in the Mediterranean.
I think we need to differentiate between several different things:
* the social organization and structures required for technologically complex societies
* the knowledge required for certain technologies
* the loss (or otherwise) of knowledge by humanity, as opposed to local loss of knowledge
When Copernicus was working out the solar centric system, he was using 1000 year old star charts dating to Ptolmey. They were the best Europe had at the time. The Alfonsine tables were just being compiled and printed as Copernicus was working.
Mostly the Arabic civilization(s) next door, which managed to retain (and extend) much (not all) of the knowledge of the Greco-Roman civilizations for several centuries.
[EDIT: Along with various libraries throughout Europe that also acted as repositories for Greco-Roman knowledge ]
