[rbanffy]

> Today's human civilization would fare vastly worse

I'm not sure I follow. While we have seen signs of loss of capabilities (such as lunar expeditions), we are far more numerous and industry is far less centralized. Our civilization went through WWI and WWII in rapid succession and rebuilt itself quite quickly. The collapse of supply chains for critical products caused by COVID took just a couple years to overcome.

> And you'd need tens of thousands of experts to have all the skills required to rebuild a "95%" version of today's world.

While it's possible some capabilities would be lost and need to be recreated from scratch, we have the tens of thousands of experts available and it'd take an event much worse than a global conventional war or a pandemic much worse than COVID to eliminate those experts.

The biggest risk for rebuilding would be politics. Those experts will need coordination to be able to rebuild our complex infrastructure, and, if whatever government is there decides we should return to a pre-capitalist agrarian society, that's what we'll rebuild. And, if that decision is made, we don't even need a devastating event to lose some capabilities we have now.

[bell-cot]

However "uncivilized" things often got, WWI and WWII were not collapses of civilization - even in 1945 Germany or Japan. Supply chains were dominated by American industry and the Allied Occupation Forces, but worked perfectly well.

Instead, look at modern-day failed states - lawless, unable to produce much beyond some subsistence farming outputs and lots of refugees (and angry, violent young men) - to get a sense of actual civilization collapse. If "government" in the US meant whichever well-armed local militia had won the last bloody fight, all 3 of the internet, electrical grid, and the petrochemical distribution systems were down - and there were no PLA occupation forces putting things back together - what would the recovery path look like?

And recall that the #1 test of "did that civilization collapse?" is whether the civilization's social/economic/governmental norms and structures lost legitimacy/authority in the minds of the (former) citizens. Outside of fantasy, you can't restore the 500AD ruins of the Roman Empire to its 140BC glory by hand-waving "now everyone just has to behave like we Romans did in the Good Old Days...".

[trod1234]

To answer your question.

The numerous amount of people create dependencies which must be backstopped which cannot be backstopped in the case of failure.

Malthus never believed we could achieve population growth above the sustainable point, but Catton's work in the 90s shows we can, and in an ecological overshoot condition where dependencies suddenly no longer get met (i.e. lower food production/famine from climate change), then you have a breakdown of order, that's violent and chaotic. By its nature unknowable and unpredictable aside from general outcomes. If you look back to the bronze age collapse, we face similar conditions without the safeguards we previously had.

The flows that created the conditions for the population boom are not sustainable, and the sustainable flows regenerate very slowly, and so when faced with sudden sustaining shortfalls, the population level will drop below what was sustainable before, and may stay there. For reference sustainable farming in the 1900s could feed about 4B globally, we have 8.3 +-0.5 (due to rural undercounting).

We haven't seen a collapse for quite a long time because society built many tools to ward off that collapse which are no longer being used. Books for example as a means to preserve and pass on valuable knowledge. Today books are used to pass on misinformation towards maladaptive behavior more often than knowledge.

> The biggest risk for rebuilding would be politics.

This never happens in practice because the politician's die in a socio-economic collapse. They were responsible for being asleep at the wheel, and the masses go after them.

The biggest risk to the future, is the economic/socialist calculation problem. A mathematically chaotic hysteresis problem that cannot ever be solved, which must be solved at the conclusion of stage 3 of any fiat currency or risk socio-economic collapse since fiat forces market collapse to non-market socialism. It may not seem like there is no market because money-printing props up market participants, but the cooperative behavior of such entities ensures the market fails, where people don't understand there is no market when the requirements are not met.

That's when outflows exceed inflows (GDP < debt growth). 2030 for the public ledger, 2023 in the private ledger that will require a bailout by 2028.

Brittle systems break under load. You also don't realize how much we take for granted the things we have. I almost guarantee you that no one, even a chemist by themselves could make commercial grade enamel wire needed for sufficient isolation for low voltage systems. You need process engineers, unit operations, engineers, something like 20-30 specialists on top of the specialized custom made equipment just to produce any wire suitable for electric motors.