It took a very long time the first time. Having knowledge, and having the resources to make use of it, are far far apart.

To drill for oil, you need drill bits. They require exotic steel. That requires high-temperature furnaces. Which requires 100 other things - ceramics, high-density fuels (not oil!), presses and breaks and grinders etc that in turn require other exotic machines to make and ingredients to find or make.

The chain of dominoes can be hundreds long. And there you are, standing in the rubble with a rock and some sticks. And you're hungry. And so is everybody else, and they want your food.

I can imagine another thousand years to get anywhere near where we are now. And it'd look completely different - combining photolithography for circuits with steam engines and slavery. All the inventions of history combined in ways that the new reality required.

It would be hard enough indeed if there wasn't a cheap way to produce at least some electricity to bootstrap the process.

And electricity is easy to bootstrap, thanks to hydro and wind turbines.

Sure, if you have wire, and magnets, and cement, and electronic controls, and pipe (for hydro). And the tools and processes to make those things.

If we imagine there's some infrastructure remaining, then there'd be a small window of opportunity to rebuild using that, before it decayed. A couple of years maybe.

And civil engineers qualified for hydro dam design, and diesel powered bulldozers and cranes, and their operators, and the mechanics and and and...

The bigger picture is not just binary today or 50000 BC, but somewhat more likely getting stuck in weird local minima / local maxima. A lot of peculiarity of USA vs euro lifestyle boils down to just the luck of the draw that we're at one local minima of public transit where they happened to fall into a local maxima, or a zillion other variables.

John Michael Greer's blog has a lot of commentary about realistic lifestyle on the downslope. One common theme is something like the secular Amish.

This "loss" and "all" talk is too binary. The real world is all analog spectrum.

Aside from "lose", there are also cultural outlook problems WRT what "knowing" means, not to mention what "power" is. And then there's topics of "education" and "wisdom"...

For example, although this sounds like a joke, its actually serious: Consider a population 200 years ago the same size as HN this afternoon trying to build a barn, a classic barn raising party. Now consider the population of HN, today, starting five minutes from now, trying to host a barn raising party presumably via twitter and flash mobs and watching youtube videos while sipping lattes at the local makerspace. For all intents and purposes we have lost the 1800s technology of community barn raising. At least we as defined as HN participants.

In theory, in about as much time as it takes a child to grow up, HN as a team, could successfully get our act together and git commit 2.0 of barn-1820. In practice it would be easier / quicker / more reliable to do the ole ageism thing and grow a new batch of fresh teenagers to build the barn. Less old ideas in the way.

That's how you lose a technology for all practical purposes.

For another example, its pretty easy to take my backyard, and industrially mechanically farm corn on it. People do this all the time a couple miles away. On the other hand we've pretty well lost the technology of growing a couple rows of carrots at a backyard scale, if you define "we" as more than single digit percentage.

  >> For all intents and purposes we have lost the 1800s technology of community barn raising. At least we as defined as HN participants.

I am pretty sure 'we' havent (in the sense 'we' = sum of HN member knowledge).

HN includes some pretty amazing members: http://jacquesmattheij.com/how-to-build-a-windmill

I don't have links handy, but HN includes people who homestead, and practice many mostly-lost arts.

My thesis is that the knowledge on its own wouldn't be enough. To reflect a later commenter, suppose we still knew how to make shale gas. We still need all the infrastructure involved in getting shale gas - which needs other infrastructure, which needs us to have some other easily available resources. All those resources might be gone.