Good answer. To see that something works means it can be made to work again. Yet first one needs to understand that it works.

en.wikipedia.org/wiki/Metallic_hydrogen could be a good candidate. See also en.wikipedia.org/wiki/Metallic_hydrogen#As_a_rocket_propella‌​nt.

+1, good new viewpoint. But also, any of that antimatter/ftl/antigravity/reactionless magicary they find wouldn't be useless. It shows us that it is, in fact, possible to make it somehow, which then helps science gain a new focus. If we find a 10x10cm sheet of strange undecipherable material that blocks gravity above it for a meter, it would be cool but almost useless in itself, sure. But it would tell us that it's possible to make it, which would cause a huge surge of interest in gravity science. Studying it's behaviour also would give us hints to a new theory of quantum-gravity.

@Neinstein While you are correct, I would consider such technologies to be somewhat near future if they can be explained by our current understanding of science. Yes, such technology would set off a slew of research into gravitational physics, but it is very much possible that gravity simply has important properties we do not yet have the tools to test for; so, until we figure out those tools, no amount of research will lead us down the right road. It's like trying to figure out how modern medicine works without having microscopes to discover germ theory.

Eventually, most of what is in the wreck will just become curious museum pieces waiting for us to discover how to discover how they work.

Unless the one thing a replicator can't make is more replicators. Maybe you can only replicate "vertically" because the special sauce that makes a replicator possible can't synthesize more of itself. It needs its own special manufacturing process. Not to poop on your ideas. Just spitballing.

@MackTuesday Yes, but the whole point of there being an exception to the rule is that there is an option where humans can do a lot of advanced technology without understanding any of it. If you can't make a replicator with a replicator, then you run into the same problem as all other found tech: if you can't make more, it's impact on the human race as a whole will be very limited.

@Nosajimiki I get your point. In my story, the aliens are so advanced that humanity can't understand 90 % of their technology, however that 10% will make a huge difference and advance human science. China, USA and India will recover certain artifacts and each side will develop different technology. But back to the topic: let's say our space expedition will find a huge pyramid with lots of gasses or a type of fuel.Or they will find this fuel inside a big spaceship. What kind of fuel (that doesnt exist in large quantity on Earth)could that be?Any ideas?

@Mishima Fuel specifically: anti-matter is probably the only thing we could figure out how that would improve on Fission Power that we don't already have. We have tons of Fusion Fuel, but no knowledge about how to use fusion for energy production. HE-3 is actually a particularly hard fusion fuel to use. You only see it in Sci-fi because it emits virtually no radiation IF you could figure out how to use it.

I have an issue with the bit about replicators: While they would be tremendously useful, there's no reason to expect that a replicator can replace the power infrastructure; nor indeed industry in general. The replication tech still presumably needs to be powered by something, and specialised production lines will always be more efficient than generic ones. What you're really describing, and what would be universe breaking, is a perpetual motion machine, not a replicator.

Where a replicator would shine wouldn't be replacing our entire infrastructure, but it would very neatly solve the "an antimatter drive is basically pointless, because you'll have the one, and no clue how it works" problem, as you could make as many as you wanted and just try random crap until something did something (until a misused antimatter drive blows up your science lab, I suppose).

I'm not sure I agree with this analogy. You're correct about an F-22 crashing in ancient Rome being not all that beneficial, but this was a time before the scientific method was developed. I feel like if an equivalent situation occurred today, modern scientists wouldn't be quite as clueless as their ancient predecessors, and might have a better chance understanding and reproducing what they found. Sure our stuff might end up looking like cheap knock-offs at first, but we'd probably get a lot closer to a working model than the Romans ever would to reproducing that F-22.

@WillihamTotland Most descriptions of FTL tech (which the aliens presumably have) intrinsically make perpetual motion possible. Even if you don't have this, you can presumably crank out something less Clark Tech like fusion generators and water hydrogen extractors and still have essentially infinite energy thanks to Earth's massive water reserves: So, to make whatever you want, just add water.

Also "specialised production lines will always be more efficient than generic ones." is only true when you compare 2 technologically similar production lines. The aliens probably use specialized replicators for making specific things, but it makes since for a colony ship designed to start up a whole new civilization to come with a less efficient all-purpose replicator to make the more specialized replicators Ad Hoc.

@Darrel Hoffman You assume the scientific method and our understanding of reality are anywhere near perfect. Every advanced civilization throughout history (including Ancient Rome) had thier own versions of the scientific method and understanding of the nature of the universe which they also believed to be nearly perfect.

In reality we don't know what we don't know. What we do know is that the smallest units of matter we have figured out so far are ~1e17 times bigger than a Plank Length, and that the universe probably has at least 6 dimensions that we do not yet have a decent understanding of leaving room for far more possible layers of existence to be discovered and manipulated in the future than have been discovered to date.

So a user manual and a rosetta stone would be the best finds?

Portions of the seed replicator could be very valuable--for instance the matter sorter/molecular filter/Maxwell's demon/Gibson's Diamond Age "Source" that produces all the raw materials needed for the assembly.

@Darren Bartrup-Cook actually it's not a bad idea, the Aliens could have a strange writing system or communicate with certain people trough telepathy,and people would try to figure it out for many years (like with a rosetta's stone). I could make something interesting from it, i'm sure.

> allows science to catch up to understanding how it all works in its own time. --- I'm afraid that is an overly optimistic wishful thinking. More likely if humans get magical technologies like that most people will simply stop even trying to develop anything new. Unless there is a clear and present danger that the original owners of that technology will inevitably come to reclaim it... Which will probably be eventually forgotten about in a couple generations, and eventually lead to stagnation of the whole human race.