when it comes to rebuilding a thing, i think whats important to wonder is would you even build it the same way? I remember seeing an article on ars about the engines for the Saturn 5. They took over a thousand hours of weld time at a level of skill and quantity that was built up during that time period. And they got them working via experimentation. Building the now was done differently. They 3d scanned the parts and used modern additive and cnc machining and used way less welds (one can argue additive metal is just cnc welding but I digress). And then simulated it in the computer. I remember a discussion about the baffles in the nozzle to stop pulsing in the combustion, that was figured out in destructive trials of this incredibly difficult machine. You'd do that in simulation now.
I likely got details wrong.
But it's to say that part of "they don't build em like they used to" also means "they learned". Look at bridges, they don't look like Brooklyn or Eads anymore. They used to build them with waaay too much steel.
That said roman concrete is a thing they've been chasing for a while
Roman concrete isn't some magical substance that we're hoping to replicate - we already know how it works - it just would really suck for the type of building projects we have now.
http://engineeringrome.org/understanding-roman-concrete/#Anc...
> Then you read something like this and realize Asimov had a point!
And also wildly over-optimistic (as is typical for SF). In the books, I think it took something like 10,000 years to loose the technical knowledge. I bet we could do it in 100.
A complicated technology like present aircraft, nuclear energy, petrochemical refining, pharmaceuticals, etc. is resting on the shoulders of a few thousand 40-something-year-olds that have the book learning of the 25-year-olds coupled with the experience and judgement that makes the technology practical, and particularly the knowledge of how to go from zero to one multiplied across many many sub-problems.
If something puts a particular technology out of practice for 20 years, many of those now-60-somethings, while still alive, will have forgotten much of what they knew, and not be suitable to put the hard hats back on and get in the field.
And this is not accounting for the effects of whatever catastrophe put the technology out of practice to begin with.
It only took a few years for the Manhattan project to create nuclear bombs once physics advanced to the point where we realized such a bomb wouldn't need to be the size of an aircraft carrier. Only a few years after that (and a much smaller budget) to make a non-exploding power reactor. There is no reason society couldn't duplicate that if we wanted.
Now the tribal knowledge does help a lot, it you still have it you can take a lot of time off. However it isn't needed.
We probably still have all the papers and journals and schematics and whatnot. What we don't have, however, is people with the appropriate training to make sense of those things. Without those people - without actual working knowledge of the technology - all that data is useless.
You can figure out what it does rather easily. Figuring out why it was done that way requires a lesson from the school of hard knocks in a lot of cases.
In the case of the nuclear industry those knocks can be rather significant.
Then you read something like this and realize Asimov had a point!