Introduction: Construction
One thing almost every genre of speculative fiction can get behind is the idea of artifacts that outlive their makers. Science fiction has everything from stargates to ancient alien megastructures. Fantasy gives us horns from ten thousand years ago or magical swords from the dawn of time. Historical fiction might offer actual archaeological finds from the days of ancient Egypt. Even horror has a place for such things, though it might spin them as mind-warping creations of elder gods from past aeons.
All of these have an attraction. Part of that is from the sheer numbers involved. The reign of the pharaohs ended over 2,000 years ago, and their civilization started producing artifacts three millennia before that; China is about the same in terms of age, as are a few other extant cultures. Prehistory stretches back even farther: tools made by modern humans show over 70,000 years of expansion, as our ancestors took themselves to nearly every corner of the earth, taming hostile lands and paving the way for our enlightened age.
Fantasy lands take this and run with it. Lord of the Rings, for example, has immortal beings who have witnessed nearly 7,000 years, and some of the things they built have stood for that entire time. Anyone who watched Game of Thrones knows that the Wall is even older than that. My current favorite series, Brandon Sanderson's The Stormlight Archive, does the same thing, putting the creation of most of its magical artifacts at a time that would make them, on our planet, older than anything else in common use.
Make the jump to other genres, and the changes are staggering. Planets and stars exist for millions and even billions of years. Thus, it's no surprise that many science fiction authors assume a long-dead race of aliens who reached their height around the time life here was figuring out how to survive on land. Their creations, monoliths and Dyson spheres and mysterious infectious molecules, remain as monuments to their glory, although some of those monuments are bit like that of Shelley's Ozymandias.
We like reading about these things. They inspire our imagination and let us escape into a world where such things not only exist, but may even be commonplace. Our modern society, taking the opposite approach, focuses on the disposable. Some of us buy new phones every year, or new clothes every month. Most of our appliances are impossible (or just prohibitively expensive) to repair, while also being designed to fail.
The pace of technological progress encouraged this until very recently. Only within the last few years have we reached a plateau, where you don't need the latest and greatest to get by, so manufacturers have had to get creative. To take one example, I had to get a new phone because my old one—which still works just fine, by the way—no longer receives OS updates, and the Let's Encrypt certificates that many sites and apps use for security will stop supporting older versions of Android later this year. There's no physical reason why my phone won't work with them anymore. Instead, it's all in software. Similarly, my laptop, coming up on its fourteenth birthday, still suffices for reading, email, and a few other tasks. It may not be able to install the latest software, but what it has isn't going to rot away.
That was the way of things until at least the middle of the 20th century, really. Because some things were expensive to own and time-consuming to make, you made them to last. To be sure, not everything was that way. Past ages had their own disposable gadgets, though likely not to the same extent as today. And archaeology gives us a kind of confirmation bias, in that the things we find are those that did survive.
But survive they did, for decades, centuries, millennia. Texts from ancient Egypt, oracle bones from China, petroglyphs almost anywhere you look...anywhere you find humans, you'll find human creations. Those places which lack history of this sort tend to be the ones where people of old couldn't be found, such as distant islands, inhospitable deserts, or high Arctic latitudes.
Material wealth
How did they do it? More pertinently, how can we, as authors, replicate such a feat in our works? We'll look at that first, then move to thinking on an even bigger scale.
First of all, anyone who has given archaeology even the most cursory glance will get a picture of which artifacts are more likely to survive the ravages of time. Perishable goods don't tend to last very long at all. We consider materials that are biodegradable to be good for the environment, but they're awful for archaeologists. Plastics degrade, paper and wood can rot; that we collectively assume our modern civilization will endure forever is one of the most frightening things I can imagine, because...what if it doesn't? (Yes, post-apocalyptic fiction can benefit from this article, too!)
Barring any unforeseen coincidences, then, most of the things we make and write today won't outlive us by too much. Maybe a couple of centuries in their original form. After that, they'll need to be copied onto new media, a process echoing that of medieval scribes rewriting manuscripts. Of course, there's always the possibility of a fortunate survival. Biodegrading requires, well, biology. If you store something in a vacuum chamber—outer space counts, though keep in mind the radiation—it can't rot.
Alas, while that works for the written or electronically encoded word, it doesn't help much for structures. As much as we might like to, we can't launch the Capitol onto a solar escape trajectory to preserve it for all time. So we need building materials that can endure, too.
Lucky for us, a lot of them do. Simple stone can last a very long time. There will be some wear from the elements, with faces becoming smooth and gaps growing, but the general structure of a stone building or monument will stand for ages. Look at the Pyramids, Stonehenge, and the Great Wall, all of which prove the conditional longevity of stone. Angkor Wat and the roads and temples of the Maya are more good examples; though not quite as old, they were built in a very unforgiving environment.
Metal is easier to work than stone. Once you get the hang of it, anyway. Its downfall in endurance comes from chemical reactions. Specifically, the process of oxidization, better known as rusting. This affects not just iron, by the way. The Statue of Liberty wasn't always green, but copper oxidizes into verdigris, which has that characteristic color—you can see it on very old pennies, too. As with biomaterials, you'd expect that oxygen is required to oxidize, but think about how common oxygen is. Anywhere there's water, carbon dioxide, or even sulfuric acid, you've found oxygen and the potential for corrosive reactions.
To sum up, what kind of construction is going to last depends a lot on what was used to make it, with its location as the other major factor. We have so many Egyptian papyri because papyrus, though biodegradable, can survive longer in the high heat and low humidity of the Sahara. By contrast, the mere four extant Mayan codices were all taken from the moist, sticky rainforests of the Yucatan long ago, where they probably would have rotted away even without the Spanish burning them. The cuneiform tablets of the Middle East were most often made from clay, giving them an immunity to fires that would have consumed paper.
Likewise, it's always news when we come across ancient cloth, because cloth—cotton, wool, or whatever—is hard to preserve. Bones from earlier eras are much more common than flesh, partly from being high in calcium, a metal whose oxidized state isn't as brittle as rust. Pottery outlasts whatever it was created to store. And, for fantasy lovers out there, a sword from the Age of Heroes might make it to today, but the leather wrapped around its hilt probably won't.
Buildings are their own story. As stated, some of them have endured for millennia. The more complete finds tend to be made from stone: take, for instance, Stonehenge in England and Skara Brae on the island of Orkney. Those made from wood and thatch, by contrast, are known more from indirect evidence such as post holes.
Of course, bigger buildings and monuments also imply some kind of civilization or, at the very least, a collective sense of purpose. In ancient times, religion was a common motive, as far as we're able to tell from our modern perch. Walls come about due to a need for protection, but they also enclose, so nomads aren't going to build them. Luckily for us authors, the reasons people of old would build something big are the same ones that would make them stand out in a story, so you don't have to do too much work there. If the men of the First Age needed to build a border wall to fight back the forces of evil, they wouldn't have made one that fell down after a hundred years.
Message in a bottle
That does, however, bring us to an interesting question you need to consider. The "time capsule" concept is common enough in fiction, so you might be thinking about such a possibility for your story. How would members of a civilization build something intentionally eternal? That is, an object—building, archive, space probe, whatever—intended and designed to withstand arbitrary stretches of time, with the goal of providing information to those at a later date.
I like the concept so much I've done it no fewer than three times in my writing. My Otherworld series revolves around it, The Hidden Hills explores the possibility of a renegade faction doing the preserving, and I even wrote an unnamed and unpublished short story that ended on an "alien artifact" cliffhanger. So I've thought quite a bit about this one.
Making something to last around a century is easy. We do it all the time, whether we realize it or not. Think about how much is still out there from 1921, how many buildings, books, and even living people remain from that time. As much as we collectively produce as a species, enough will get through a hundred years that we don't have to worry. Similarly, we don't have to worry about encoding our message. Modern English and ASCII should still be understandable in 2121, if nothing else. Although we would want some kind of durable media. MicroSD cards probably won't cut it.
Adding another order of magnitude gets us into our first real problems. Yes, there are quite a few structures from the 11th century that are still in use today, and as something other than UNESCO Heritage Sites. Many of the grand European cathedrals dating back to this era, for instance, have been renovated so much that it's hard to call them the same building, but original parts remain. On this scale, you have to worry about things like fire (the Great Fire of 1666 that destroyed much of London, for instance) and other natural disasters. Coastal cities may have to endure hurricanes, while earthquakes can strike just about anywhere.
Social changes also come into play over the course of a thousand years. How many works of art are lost to us forever because of zealous destruction in the name of religion or ideology? The Library of Alexandria and the Nazi book burnings might be separated by over 1,500 years, but they are perfect examples of the kind of cultural destruction that a time capsule has to avoid. Witness also the Taliban's detonation of Buddha statues or rioters tearing down those of American icons—priceless pieces of history callously obliterated, and the same fate might befall any artifact from ages gone by.
Even if the medium survives a thousand years, that's no guarantee the message will. With that length of time, linguistic evolution can render a message unrecognizable. Chinese characters, widely considered the most conservative and enduring script on the planet, still don't let a native speaker read a thousand-year-old document with ease. Cultural data points will be long forgotten. Entire empires may have fallen. Anything such a message wants to say will have to be expressed in the simplest terms possible, with no references that assume common ground. Not even place names, because they might all be different now!
Going past this point, we start looking at eras, what I like to call the "grand sweep" of history. Most Christians would agree that books written around 2,000 years ago remain relevant today, but so much of their content isn't. Ignoring the obvious language barriers, an Iron Age carpenter wouldn't have the slightest idea what we're talking about when we go on about computers, phones, TV, refrigerators, capitalism, fossil fuels, or feminism. He wouldn't recognize the tools we now use for his trade. But the converse is no less true: we wouldn't understand his lifestyle, either. The context of his life would be so different from ours that we'd have to start a conversation almost from scratch.
Oh, and that's with an unbroken chain of history. Take that part away, and you really are starting from scratch. We can't read a word of the Indus Valley script. Its context was completely lost, so now we have no way of knowing whether the seals we've found tell us a person's name or the directions to a secret stash of gold. Our descendants thousands of years hence may have the same problem, depending on what happens in the intervening generations.
The big time
Something that can stand the test of time for all of human history is already supremely difficult to construct. Now think about going into space. Those ancient aliens? They're going to have an even harder time.
True, once something's in space, in a stable orbit or on a trajectory that keeps it from running into, say, a planet or star, it's going to stay for a good, long while. Thousands of years, easy. Millions? Possible. Billions? Maybe not, but plenty of people are thinking about it.
On our humble planet, long stretches of time like that start running into big problems like plate tectonics, ice ages, evolution, and asteroid impacts. There have been a number of stories exploring the deep past and the deep future of Earth, stretching all the way back to The Time Machine by H. G. Wells, and some of them explore the hard science involved from the far-future evolution of humans, for instance, to a dinosaur-era civilization or a precursor race wiped out by the Late Heavy Bombardment.
Messages on this scale have all the troubles I've described above and more. You can't guarantee that your time capsule will stay in place. You can't guarantee that it'll stay on land, or even (after a certain point) on the same continent. Going into the millions of years, you can't assume its recipients will be human. And, of course, we have the ultimate fate of the world, so any terrestrial message has a definite expiration date.
Out in the void, it gets marginally better. You don't have to worry about losing the message anymore, but you still have to handle the part where you may be dealing with beings who share no context at all with your race. An extraterrestrial beacon won't be some kind of galactic Wikipedia. No, it'll need to start with the basics, identifying things like mathematical axioms, laws of physics, and subatomic particles. Then you can begin to discuss things like the physical nature of your species. Then you can work on the mental and social aspects. And only then can you worry about philosophy and explaining how to talk to the astral beings of the fifth dimension about reversing the Big Bang.
Messages from ancient aliens, then, may not look like messages at all to the untrained eye. There's just too much difference. Just as nonspecialists see nothing more than a string of pretty pictures when they look at hieroglyphs, decoding the Prothean library is going to be a long, hard struggle that starts with simply understanding that there's something there in the first place.
In your story, a lot of that can be swept under the rug, of course. Unless you're actively writing a decipherment story, you don't have to deal with the specifics where they aren't necessary. But it does help to think about them. Especially in sci-fi, but even in fantasy it may help to consider just how unlikely it is that the tales and artifacts of old make it through time unscathed. Magical preservation—or, following Clarke's Third Law, a kind of technology so advanced that it's indistinguishable from magic—may be the most viable method, assuming it fits your setting. In a space opera, the first alien transmission might say, in effect, "Here's how to build a universal translator." And interpreting the message may end up worthy of its own story.
This one was a bit more rambling than usual, but that's because I was trying to cover such a big field. I do like subjects that work with multiple genres, though. So many of my stories fall between the labels of "fantasy" or "sci-fi" that I think it's better to consider worldbuilding from all angles, rather than just from the perspective of one specific genre.
As always, thanks for spending time with me today. Remember to leave your comments and tell your friends. And never forget to keep reading!