They are a group of fed up people in a third world country who somehow acquire/buy land in a remote place near the Himalayas. Ignore the powers like China trying to conquer them. Is this possible in 2050? For them to never mix with others for the next 5,000 years and develop their own technology.
Almost certainly not
Human Resources: 10,000 people is the size of a small township in modern terms. It is much smaller than a single university, once you include the supporting infrastructure. There is no way that this number of people can even attempt to maintain a modern technological capability. This number of people is probably enough to maintain an Iron Age level of existence - 90% of the population are farmers, leaving the remaining 10% to be more specialised craftspeople, miners, builders, administrators etc. If they carefully plan their regression to low technology then they may survive the process, but they will probably end up at a much lower technology level than the Amish.
Material Resources: Even if the 2050s you envisage includes super-capable generalist artificial intelligence so that the humans do not need to individually learn the thousands of individual medical and technical specialties that a modern society depends on, there is the problem of resources. A technological society needs access to pretty much every element in the upper rows of the periodic table, and there is no one place on Earth that possesses all of them. (Not to mention that you come back to the human resources, or lack thereof, when you need to mine and refine every single element.) A single location will simply starve for specialised resources - iron is probably available, so an Iron Age existence is theoretically possible, but that is as much as can be realistically hoped for.
Environmental isolation: Let us assume for the moment that all the bordering nations have signed treaties assuring the isolationist group that it can remain undisturbed. All will be fine - as long as no pollutants from outside drift across the border and devastate the population, or, conversely, the isolationists let pollutants drift across the border to annoy their larger and more heavily-armed neighbours. The same applies to any rivers flowing from the isolationists into its neighbours - if the isolationists pollute or dam the river/s then their isolation will come to a sudden end. Frankly, these considerations alone will mandate that there is diplomatic contact between the micro-nation and its neighbours.
Social and political continuity: There are no industrial / post-industrial human civilisations that have lasted for even a few hundred years without major changes. Maybe societies will stabilise in the next few hundred years, but the experience to date points otherwise. Over the next 5000 years, it is almost inevitable that - assuming Earth remains inhabitable - someone is going to make the call that "those poor people have been suffering based on their ancestors' decisions for too long now, it's time we helped them." Or the nation will suddenly become strategically valuable to one or more surrounding nations. What is even more likely is that the children or grandchildren living in the Iron Age isolationist society will see the shiny aircraft, satellites and other tech toys and want to get out. I would be astonished if this concept lasted more than 30 years - once all the founding fanatics get old and the initial supplies have run out the population will rebel, especially the women. ("What do you mean, you want contraceptives and a decent chance of surviving childbirth?")
- there are not enough people to maintain modern technology, let alone develop more;
- there is no place on Earth with sufficient variety of resources in the one place for maintaining a high technology society;
- diplomatic contact is needed because modern society creates effects that cross borders; and
- sooner or later either the isolationists or the surrounding nations will decide to break the isolation.
In the hypothetical scenario you're describing, there would be a multitude of factors to consider. Theoretically, a group of 10,000 people could start their own independent civilization, but the practicality of such an endeavor, especially in terms of remaining isolated for 5000 years, would be extremely challenging. Here's why:
Land Ownership and Sovereignty
Acquiring land is one thing, but having the sovereignty to govern it as an independent entity is another. International law would be a significant hurdle. Land ownership doesn't necessarily grant the right to start a new nation or civilization. The land would likely still fall under the jurisdiction of the country in which it is located.
Sustainability and Self-Sufficiency
For a group of 10,000 people to survive and thrive, they would need to be able to sustain themselves. This would involve farming, hunting, or gathering for food, access to clean water, the ability to construct shelter, and a means of dealing with waste. This would also involve creating and maintaining an education system, healthcare, law enforcement, and other societal infrastructure.
Being near the Himalayas, the group would need to be able to cope with a harsh, cold climate. They would need to develop appropriate technology and skills, not only to survive but also to grow food, build homes, and maintain their society.
Developing technology in isolation could be problematic. Today's technological progression is built on centuries of accumulated knowledge and global collaboration. While they could potentially develop new technologies on their own, their progress would likely be much slower than the outside world. They might also face issues related to lack of resources, as not all necessary components for advanced technology may be available in their location.
Social and Genetic Factors
Without any interaction with outside communities, the group could face social and genetic challenges over time. With a limited gene pool, there could be an increased risk of genetic disorders. Socially, the group would need to establish systems of governance, law, education, and cultural practices that could sustain them through the centuries.
While theoretically possible, the practicality of a group of 10,000 people starting their own civilization and maintaining it in complete isolation for 5000 years in 2050 would be fraught with challenges. It would require careful planning, significant resources, and a lot of luck. Even then, maintaining complete isolation from the rest of the world and the influences of global politics and climate change, among other factors, would be extremely difficult.
What is the technology level of these people? In the extreme case, where they may have Von Neumann self-replicating_machines to provide for their needs, then all they need is a minimum viable population which could be less than 1000. But more than the Lykov family.
In a less extreme case, they may have most of their needs provided by the machines, but they maintain the machines and do the non-routine repairs. They may, for instance, have a machine shop for making metal parts so they can make most of the rarer components that they do not keeping stock.
They could write integrated circuits directly using ion beam machining and implantation. This will be a lot slower then the current resist techniques, but does not need the huge production lines.
If they have technological neighbours, they might secretly buy items that they cannot easily make for themselves. They could ask for parcels to be delivered to and collected from some remote house when they knew it was empty. That compromises the isolation specified in the original question, but it might be the more sensible option, and a good part of the plot.
Edit: This is what the Amish do. You can buy their hand-made furniture from websites.
At first glance it seems possible. We look at examples such as the Northern Sentinel Island tribe, which has been isolated on their island, it is estimated, for 55,000 years (fifty-five thousand). So, why couldn't you do what you want to do?
Isolation on the mainland isn't possible
The North American Indigenous People are proof that a group of people geographically unseparated from other peoples simply isn't possible. But they're not alone. I can point to groups of people separated only by land all through history as examples that people won't be left alone. Frankly, even the Sentinelese are unlikely to have been left alone for 55,000 years. They likely had contact with the surrounding island-based tribes. It's thought that their violent isolationism is a result of the devastating effects British colonialism had on their neighboring tribes.
My point is that it's actually very, very hard to achieve true isolation for any amount of time. Your people will have the devil of a time procuring land that isn't claimed by one nation or another, and that means connecting with tax collectors and bureaucrats, participating in national drafts, and dealing with law changes that will be contrary to your isolationism. And that ignores the tourists, thrill seekers, activists, door-to-door salesmen, and LDS Missionaries1 who are absolutely sure your people must be contacted.
The odds of a national benefactor allowing your group to remain isolated for 5,000 years is, frankly, unbelievable. It's better if they're on an island of the sea, one that's generally considered to be in international waters. But even that's a hard sell for other issues. Read on, MacDuff!
5,000 years is a whomping long time
First of all, 5,000 years? It's impossible for anyone to tell you with any degree of rational certainty that a civilization can last for 5,000 years. The longest we have to date (that we can prove... and I could be wrong about this...) is the Chinese civilization clocking in at 3,500 years.
However, we're playing fast and loose with the word "civilization." did the Chinese "civilization" continue through changes in government that changed the society? Today's national China is not the national China of 1,000 years ago. The Viet civilization has been around nearly as long, but most people don't contend that theirs is a long-standing civilization because it's gone through so many strong political changes. Theoretically, civilizations in Africa should clock in at the longest — and yet they don't even appear on the list because Africa has been so unstable and so ununified. If we really stretch it to "oldest recorded civilization in human history" I think it's the Mesopotamians beginning 6,000 years ago that take the cake. 5,000 years is a length of time about which we humans can't prove much of squat. We're not even 100% sure we have the estimated historical time periods dead-on right.
Therefore, asking if a civilization can remain in isolation for 5,000 years is, IMO, a hard "heck no!" Even China didn't remain in isolation. In fact, if anything, China became really good at absorbing conquering people and turning them into Chinese people.
Technology makes things worse
One of the reasons the Sentinelese are left alone right now is because of the massive disparity between their tech and the tech of the rest of the world. They're so primitive that they have the sympathetic support of several organizations world-wide to preserve their isolation. In other words, they're not in isolation simply because they want it. Land a platoon of modern marines on the island and they'll be in submission in a day or two.2
Make your group's starting tech more-or-less the same as everyone else's and the impact of technology is meaningless (almost... read on, MacDuff!). 99.9% of today's technology was invented in the last 150 years. What technology we'll have 5,000 years from now will be like magic — and eavesdropping tech will most certainly be among that magic. Your civilization will keep up because, while they want to remain isolated, they won't remain in isolation. Unless they choose to, in which case they're choosing to walk away from keeping up with the technological Jones'... and that means they might as well start by divesting themselves of all technology and plant seeds with sticks and watering them with pig bladders.
Note that it could be suggested that after 5,000 years your civilization will be as primitive as the Sentinelese are to us right now. That might rationalize isolation if there were still activists stumping on your group's behalf. But I suspect that isolation will be broken long, long before that disparity would make a difference. (And I also suspect that's not what you want....)
Population growth is not your friend
A substantial problem your people will have with starting with modern technology will be all the advantages relating to population growth. So, let's use 1950–2020 and scale the number to see how fast your community might grow in 5,000 years without the imposition of storybuilding restrictions (like war, disease, or social/political restrictions).
- World population in 1950: 2,499,322,137
- World population in 2020: 7,840,952,880
- Percentage growth rate: 213.72% over 70 years or 3.05% per year
- Proposed starting population: 10,000
- Estimated ending population: 1,526,594
Someone will have noticed your population and decided it couldn't live in isolation long before it got to 1.5 million.
Conclusion Part 1
There's nothing wrong with you setting a rule for your world that says your group has formed, chosen to be isolated, and remained so for 5,000 years. It isn't realistic and there's no historical basis to support the idea, but that doesn't stop a good author.
Honestly, your biggest sticking point is the 5,000 year thing. It's popular for authors to come to this Stack and ask about breathtaking lengths of time like that. Can you imagine what a human being in 3,000 BCE would think about our world today? They spent something like 90% of their day gathering/managing, storing, and preparing food. In first-world countries someone not employed in in the agricultural sector might spend about 5% of our time doing that. If such a person came forward in time (ignoring the whole dead-due-to-modern-diseases thing), it might not even be possible for them to integrate in any practical way. My mother uses bluetooth-connected hearing aids to talk over her cell phone. Our friend from 5,000 years ago would think she was stark raving mad — and even if such a person could understand her language (that's a problem in its own right), what my mother is talking about would have no meaning to that person. It would be gibberish. Mad gibberish. Burn-at-the-stake-to-make-it-go-away-before-the-crops-fail gibberish.
Why on earth do you need such an impractically long period of time?
Anyway. From a "realistic" perspective, M. Night Shyamalan's The Village this is not. I can't believe it on a realistic scale.
But could I believe it on a suspension of disbelief scale? Sure! And you wouldn't need to go to that much effort to establish the basic credibility that would allow me to suspend my disbelief and move on with your story.
Conclusion Part 2
If you want to suspend my disbelief you need to:
- Come up with a brief explanation of how you're going to manage population control over 5,000 years so your neighbors never see you as a threat.
- Briefly explain how you procured a reasonable piece of land that is good enough for basic agriculture but not so great in any other way (especially mineral wealth) that your neighbors would see it as desirable — and then briefly explained how you got the necessary treaties in place to be left alone long enough to be eventually ignored.
- You'd need to completely ignore 5,000 years of global politics, like world wars (we've had two in the last 125 years...) and changes in government and civil unrest and well-meaning-but-careless-of-private-property-law activists who are absolutely sure that your presence in your little valley is disrupting the life cycle of the Tibetian Woolled Springing Butterfly... You get my point.
Do this briefly and sparingly... then move on with your story. The reader will forget quickly enough that the premise of your book doesn't make sense. It's worked for every time-travelling story that's ever been told. It'll work for you. Just spread a little peanut butter and jelly to get past all that and move on.
So say we all.
You did say, "like the Amish." A number of groups have maintained considerably close ethnic unity, remained fairly isolated, and nevertheless enjoyed the privilege of surrounding civilization. The Jews come to mind. If what you're talking about is a group that's culturally isolated and not physically isolated, then you can achieve that with almost no trouble at all. Your group might eventually be seen as a cult. But that's well beyond suspension of disbelief. In that case, it would be worth looking into how the Amish deal with population growth (they reach a point where they split families and create new colonies).
1 Full disclosure: I'm a happily practicing member of the Church and served such a mission myself. So I'm allowed to poke fun at us.
2 And dead from modern disease in a week or two. That's another reason why they're kept in isolation. We've almost maybe kindof learned that you can't get involved with primitive peoples without a fairly permanent consequence.
Yes, that's enough to survive
While they won't be able to maintain a complex supply chain, there's enough people to have a functional society, maintain a low level of technology, and survive for 5000 years.
To make it more advanced, have a reclusive billionaire help out
A billionaire could gather all the geniuses of a third world country, import a lot of expensive technology, and negotiate with the nearby powers to keep them away. That's a popular premise, like with Bioshock or other places with reclusive and advanced cultures.
10k people are much too many to work as a big clan for thousands of years. Real-world self-sufficient clans/tribes consist(ed) of very few people; it was possible for everybody to know everybody else, which lead to them sticking together exceedingly strongly. They also had very strong us-them mentality (and if there was no other clan to establish a border with, then it was the wilderness surrounding them). They were basically limited by the resources which fed them - be it animals or crops. For your 10k, you'd need an awful lot of land to support them, leading to all kinds of issues - you can't really do that in a low-tech manner. Unless you have hefty power structures which lead to what we witnessed in reality since written history - frequent wars. And without power structures, your 10k might as well split into 100 clans of 100 persons each - which in turn will turn against each other.
But 10k is also much, much too few to have a self-contained high-tech society. Supply chains going into everything we consider high-tech are so broad and deep... and it's not like you could have a single expert for any given topic; you always need a community to pass on the knowledge, hone skills (education) and so on and forth.
So while you can certainly try and give your culture a good starting point - i.e., perfect land, no border disputes through some magic, no foreigners spoiling anything, as much starting resources and well-meant policies as imaginable, and a selection of humans so peaceful and willing to make it work as in a good old Star Trek episode, you will by necessity see substantial decline over the years. At some point, a tyrant will pop up. At some point, a natural disaster will eradicate half your crop. Eventually, your society will develop dysfunctional power structures. Or if all that does not happen, it will just not be enough.
The good news is, all these issues give great fodder for making an interesting book. Nothing would be more boring than having an awesomely functioning society that has no issues for 5000 years, wouldn't it?