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Comment by twelve40 | Hacker News Reader

> following all of the detailed recipes that had been optimized over the course of many centuries

i wonder how all those detailed recipes were passed around for many centuries and now all is gone. Was it all passed down verbally?

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Some of it was "stone from this volcano" and then it was mined out. They didn't know how to choose a substitute.

In the 6th century, big volcanic eruptions, low temperatures and plagues bringed a dark age in Europe and other parts of the world. A large part of the population died. Maybe those recipes were lost during this period.

I don't think the knowledge is gone, we could make that or maybe even better. The point is nobody wants it, most things we build need to be torn down after at most a few decades anyway.

The knowledge is actually gone, like Damascus Steel (what we have today is just a visual reproduction) and Greek Fire.

For a more recent example: we already "forgot" how to make the spaceships and rockets that went to the moon. Even if you had the full plans - and apparently we don't, a lot of the materials and processes are not around anymore and would have to be 'reinvented'.

We have a pretty good idea of Damascus steel at this point:

- We know that early Damascus examples were made from imported Wootz ingots, which we absolutely can recreated.

- The high quality of the blades were due to naturally occuring impurities of molybdenum, vanadium, and chromium, all of which are used in various modern alloys.

- Forging and heat treating processes varied greatly across historical blades called "Damascus" and we have sequences that create both visually and metallurgically similar results.

Not quite.

For Damascus steel and Greek Fire we almost certainly still have the knowledge. We just lack a document to tell us that "Greek Fire" matches formula #44 of napalm specifically, or what specific process an ancient smith actually followed.

For the spaceships, no, we have the plans, but they're long obsolete. They're made for ancient, manual equipment nobody uses anymore, and old materials that have since been improved on. We technically could dig up and restore ancient manual milling machines, recruit retired engineers and special order obsolete materials and parts, but what for? Unless you're engaging in experimental archaeology what you want is a rocket, not the rocket that has a nostalgic feel to it, and it'd make far more sense to make one with modern methods.

For the spaceship example, I’m fairly certain that we do know the theory behind how all those materials and processes are created though. It isn’t that we lost the knowledge, but the infrastructure. Recreating the infrastructure to create the materials to create the rockets is possible, it’s just that recreating entire processes from scratch when they had already been phased out of our modern structures would be outrageously expensive, especially just to construct rockets.

I was referring to the knowledge of how to make long lasting concrete, not necessarily specifically how the Romans did it, but I guess I could've been clearer.

The answer is still no, we don't know how to make long lasting concrete with modern techniques either apparently. Hence the research.

Especially steel-reinforced concrete, the lifespan is only 50-100 years. The only exceptions are massive structures like dams that will probably last a couple millennia.

Right but the thing is neither did the Romans. The only reason roman concrete lasted so long is it didn't use steel reinforcement. All of the structures we have from them are carefully designed to only use compression.

So why didn't the researchers just ask one of the people who knows how it's made, instead of wasting all this time conducting tests and doing spectroscopy?

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