I am writing a story where humanity has advanced technology, but I want to give a justification for why they are still on their planet. Here humanity has advanced ai, superconductors, laser weapons etc. what excuse can they have for not leaving the earth.
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Question: what actual constraint, or self-imposed constraint, would a high tech species like humanity prevent from developing space travel ?
Space is dangerous
Space for humans (and life in general) is dangerous and costs a lot of energy. What we shoot into space requires a ton of safety features, as it needs to be able to withstand a wide range of powerful electromagnetic waves as well as large sudden heat changes. In our solar system we're relatively very well protected. Big planets catch a lot of debris, preventing the debris to reach the Earth. In addition, the make-up also reduces the debris floating around the planet.
As @Thorne his/her excellent answer states, debris might be so much that anything going to space needs ludicrous amounts of armour. This increases weight, making space flight not practical. The rockets themselves are too large to get all that weight into space. In addition, many instruments like solar pannels become unlikely to work and the armour isn't a guarantee to prevent damage. Still I think this answer doesn't go far enough to be fixed with a simple comment.
A planets atmosphere and magnetism protects the surface against a ton of dangerous waves. The star alone can already pump out so much power on every wavelength, from huge radiowaves to the tiny gamma rays. These can scramble, disable, destroy, or overheat spacecraft or simply prevent good communication with anything shot into space.
It might also be that there's too little to see, so they don't realise the full extent the universe might offer them. If a cloud or many strange phenomenon, like time dilation or simply too much noise blocks further view of the universe, it might seem they are quite small and alone. With practically nothing to interact with, they might not realise many benefits of space, or might just have a few niche things out there.
Maybe they could see everything. A single planet around a hospitable star, but anything else has floated away or has been absorbed by the star or planet. You might see other stars, worlds and galaxies, each so far away you know you'll never reach it. Anything they would do in space then seems a useless endeavour. Better to stay on your planet. See what you see, make your lives as best as possible, and don't venture towards the unreachable stars.
Their home contains a mass much greater than our Earth. Getting to orbit is spectacularly expensive and energy costly.
That's just for satellites. Crewed missions require much heavier-built ships for the pressurization, and experiments have proven a zero gravity environment causes them severe health problems. Beyond several hours is fatal.
So why bother? :) As a bonus they don't have a moon, and the next closest planet would be a year's travel with their available tech. Getting there would be a massive "all or nothing" investment which they haven't yet made.
Our solar system has a whole lot of potential targets of space travel, from the asteroid belt to various planets and moons (and Moon). Those targets also act like potential stepping stones of various degrees of difficulty to reach (Before going to Neptune, you'd probably first test waters with something closer to home, right?).
If your solar system is devoid of other planets and smaller planetoids for whatever specified or unspecified reason - there's no learning curve. The closest goal you have after "get into the orbit" is straight on "interstellar travel". Which is like asking to cross the Pacific right after you hopped over a small creek. So the most that you can do is to host a couple of space stations in the orbit, that would be never of any use beyond some limited scientific or military value - everything else requires experience and practical knowledge that you just have nowhere to obtain.
This was the driving force behind the Krikkit, the main antagonists of Douglas Adams, Life the Universe and Everything:
The people of Krikkit were surrounded by a Dust Cloud, their single sun with its single world, and they were right out on the utmost eastern edge of the galaxy. Because of the Dust Cloud there had never been anything to see in the sky. At night it was totally blank. During the day there was the sun, but you couldn't look directly at that so they didn't. They were hardly aware of the sky. It was as if they had a blind spot that extended 180 degrees from horizon to horizon.
The reason they why they had never thought to themselves "We are alone in the Universe," was that until one night, they didn't know about the Universe.
Does it have to be our Earth, or can it be an Earth-like planet?
One good way to trap a species on a planet is to make the planet just a bit heavier than Earth, thanks to the tyranny of the rocket equation (NASA):
If the radius of our planet were larger, there could be a point at which an Earth escaping rocket could not be built. Let us assume that building a rocket at 96% propellant (4% rocket), currently the limit for just the Shuttle External Tank, is the practical limit for launch vehicle engineering. Let us also choose hydrogen-oxygen, the most energetic chemical propellant known and currently capable of use in a human rated rocket engine. By plugging these numbers into the rocket equation, we can transform the calculated escape velocity into its equivalent planetary radius. That radius would be about 9680 kilometers (Earth is 6670 km). If our planet was 50% larger in diameter, we would not be able to venture into space, at least using rockets for transport.
It really is tyranny. Building a rocket with 96% fuel seems like a stretch to me personally, so perhaps less than a 50% increase could be enough to trap us. At least until we create nuclear-powered spacecraft.
If you cannot make the planet heavier (or the fuel less efficient, or metals weaker), then Kessler syndrome would be a very realistic trap. Note that you don't have to get there gradually - some nation may have intentionally triggered Kessler syndrome in a past conflict.
Space Junk
Already the Earth is surrounded by thousands of pieces of space junk, each one capable of knocking a hole in satellites and spacecraft.
If a series of disasters caused a cloud of space junk that would destroy any spaceship trying to leave the planet, people would have no choice but to stay planet bound until such a time that the cloud cleared enough to reach space.
The idea you are working with is something that is in line with an idea called The Fermi Paradox - basically, if the universe is as old as it is, and if we believe that Earth and life are not uncommon, why do we not see evidence of aliens all over the place?
There are a number of solutions to the question, but one is that other civilizations do not engage in space travel, and hence do not have a large influence beyond their own planet. A further sub scenario to that solution is that the civilization feels no need to travel in space. Perhaps all of their needs are met, and they don't see why they need to make life more difficult by traveling in space.
You can also go the more realistic route that things just get in the way of traveling in space. Although at first glance it may not seem too difficult to justify that people just didn't find space important - after all, many in our world think that space exploration is unimportant -
There are many converging factors that have led to space exploration, or would have led to it eventually. They are as follows:
So it is a complex question. Your society needs to have reasons why it pushed to get super conductors and energy weapons but did not choose to go into space. If you are striving for realism, you will want to look into what technologies and societal impacts have come from space.
Personally, unless your story is more focused on stuff surrounding space, I wouldn't sweat too much over it, mentioning only something like "it's arrogant to raise yourself to the heavens" or "space travel is considered impossible, or dangerous" will probably be enough to justify your choice.
It's fairly hard to justify them having zero interest in space at all. Satellites are immensely useful for studying weather, communication, and lots of other things.
But beyond that? We don't need to go further.
There's lots of minerals on earth, lots of resources and people. Space is barren and dangerous.
Perhaps they sent several missions out, and did a routine, land people on neabry planets, but long term missions resulted in accidents that killed everyone involved, and were extremely expensive. Space is dangerous.
As such, nobody wants to invest billions of dollars in missions beyond the planet. They can continue to tech up, and advance the planet rather than wasting billions on speculative missions into space which may well go badly.
There's no guarantee that any particular world they would want to colonize would be habitable. Not only are Goldilocks-Zone worlds extremely rare, they're also probably not going to be habitable anyway.
You see, elemental oxygen has extremely round heels; it's always looking to hook up with another element. For a world to have significant quantities of free oxygen it must have some sort of mechanism to keep it free, i.e. life. Ethical issues aside, the natives (intelligent or otherwise) are probably going to react rather badly to colonization efforts.
Nobody wants to face the possibility that their voyage to the stars will be in vain.
Technological advancement in many areas need not equate to the same pathways of technological advancement nor pursuit of the same technologies we have historically produced. There is a lot of, call it luck, in the advancement of any given field of science, many discoveries are made by individuals who refuse to take no for an answer and others due to happy accidents.
We owe much of our rocketry technology to one scientist who took Nazi money and worked through a series of near continuous disasters because he had a dream to go to space. He perfected a technology that very few people around him thought could ever be successful only because of his personal obsession. Without someone in his position, with his drive, proving that it could actually be done space rockets may have been consigned to history's giant list of "stuff that would be great if only it worked". Once there was a consensus that the technology didn't work more reasonable governments wouldn't throw good money after bad chasing it. Especially not in a history burdened with a staggeringly expensive development program that went nowhere and no example of what a working ballistic missile can actually do as a weapon beyond exploding on the launch pad.
What for ?
Space has been explored with probes and satellites but people are content on earth, why would they leave ?
"Humans in space" is a pretty scifi dream but there's few pratical reasons to go there. And if your civilization has overpopulation problems, make colonies in the sea or underground, it's far more pratical and cheaper than sending people in space.
The Matrix
Instead of expanding outward literally, they build giant computers and uploaded themselves. They can efficiently house trillions in a virtual world will efficiently siphoning power from their local star. No need to go anywhere for billions of years.
In 1961 the first man entered orbit, 1969 man first visited the moon. Since then, a little over 500 people have been to space and a dozen have walked on the moon.
Human technology has evolved considerably in the 50+ years since man went to space. Vast improvements in technology have been made, and to be fair that does include space technology, but it seems obvious that space just isn't something that humans as a whole are motivated to conquer. We certainly have AIs, lasers, and super conductors!
Without motivation, humans may find more pressing or interesting problems to work on.
Obvious omissions from the otherwise great existing answers are: political problems, money problems. These are often linked.
Maybe no large nations were created. What looks like the USA in our world ends up breaking down into just the smaller, individual states as their own countries. Canada, Russia, China, India, and other large countries never formed or were destabilized and broke down into small, regional dynasties or other governments. Because of this, it would take a large group of these countries to be able to afford a reasonable space program.
A program like NASA takes billions of dollars to fund every year. Without the cooperation of multiple small countries, it just isn't possible, and the lack of trust among these small countries makes it impossible.
Politicians just don't care about space travel. They don't think their voters know anything about it, so disregard their requests to do anything about it. Russia just wasn't interested, so never launched Sputnik, which never spurred the Americans to reach the moon.
Besides, there's better things to be spending money on, like feeding the poor, education, paying people living wages, keeping taxes low, paying off the national debt, preventing climate change, and more. And in this world, those things are actually being done. With these programs making life better for everyone, there's no pressing need to leave the planet. Asteroids? That only happened to the dinosaurs and in video games. It's not a real threat, is it?
Money is not stable. The stock markets are manipulated by the AI, big banks, and stock brokers so only the rich have any money. They've also manipulated the laws so they don't have to pay taxes and they don't have to pay their workers much. This means the taxes brought in to pay for governmental projects is severely limited.
It's so limited that roads turn to gravel before they are repaired, bridges fall down and have to be replaced with barges, damns burst and aren't replaced, welfare programs are non-existent, and about the only thing the government can manage is to stay out of constant wars for limited resources, including food and water. They don't have time and money to spend on programs that take food and housing away from citizens.
There is advanced technology for the rich, but squalor and starvation for the rest. The world's rich have 90% of the wealth (instead of ~43%).
With this massive wealth gap, and simple short-sighted greed, the wealthy don't care about space. They don't have any interest in leaving the world they run. They also don't care to risk their lives just for a ride, even if it is into the history books. The only thing they want to be known for it being the richest person in the world, and that can change daily, so the longer they remain the richest, the more status they get.
They also don't care about spending the billions of dollars a year it would take to get into space. To them, it's a massive drain that would prevent them from being the richest person, so that's just out of the question. There's no Return On Investment, which makes that spending pure waste, so it goes against everything they've been taught is important by their family, friends/social clique, and world history.
They have multiple aggressive militaristic civilizations on their planet.
Any time and resource spent on interstellar or interplanetary travel could be spent on more advanced weapons.
One can argue that space travel can bring in resources, but they are long term investments especially interstellar travel without FTL, while you divert resources on space travel you enemy will build AI controlled army to conquer you with less time and resource.
I took MolbOrg advice and clarified the answer.
Even if a civilization build a spaceship, other civilizations can develop weapons such as rockets to destroy with the small fraction of the cost.
Only orbital devices such as spy satellites or armed space stations would be strategically feasible.
There was an unexpected disaster - Enormous solar flare wipes majority of the life on Earth, destroys most of the infrastructure except for fortified military facilities, where technology survives, cuts off, by destroying orbital facilities, off-planet settlements and causes their demise.
Better yet, let survivors know this happened due to actions of hostile alien species and humans need to lay low for "a while".
There is no way to stop humans from exploring space except for denying them access to resources needed and to the surface. Space junk can be cleared with ease given sufficient level of tech, so by my reckoning only way to get what you need is to force them into underground hiding.
In our world, we went down branches of technological discovery to reach rocketry and space travel with a potential eye to colonization on other bodies. In your world, there wasn't a need or desire to do that.
Likewise, a spaceship or satellite isn't one invention. It is the culmination of many technologies and ideas yeeted off the planet at high velocity for our own reasons. Given the question's statement of having advanced AI and supercomputers and laser weapons, an idea is a lack of easily acquirable structural materials in the quantity needed to actually build a spaceship could be a cause here.
A third option is that it could be that early on the world learned of climate change and renewable energies and moved harder on developing those technologies and leaving the fossil fuels in the ground where they belong. The presence of laser weapons suggest that your world has moved beyond gunpowder and other chemical weapons. Perhaps they have moved from chemical energy fast enough to not develop the ideas to rocketry?
Building on the first point, perhaps there is a lack of pressing reason to develop space travel at all. Lacking world-spanning wars, there might not be the development into weapons delivery systems that would lead to being used to go to space so they went in the computing direction instead.
If they have enough resources for their population, then there might not be the same drive to leave the planet because everyone can have what they need. I would hesitate to call it post-scarcity, more that there isn't the level of scarcity that would drive exploring space for resources
These two reasons are still branches of technical development, but instead of different decisions on how to advance, it is about pressures for advanced caused by events.
For a more sci-fi twist, a more advanced alien species are actively sabotaging the planet's ability to leave it. Why they are doing it is unknown, their motives inscrutable. All those on the planet know is that any travel beyond the orbit of the planet fails for reason.
It's a lot more random sci-fi but it is a more outside the box reason as to why they haven't left the planet.
I'm not sure if this is still scientifically valid, but there was a theory that came out in the last decade that genetics may have a heavy influence on the desire to explore. It was theorized that a big difference between homo sapiens and Neanderthals was this gene, and that explains why there was very little migration of Neanderthals compared to humans. It may explain why some people seem to be natural explorers who are willing to sail across an ocean not knowing what is there and some are content to never travel more than a couple miles from their birthplace.
This may all be just popsci nonsense, but if accurate perhaps there could exist intelligent life on other planets who are genetically predisposed to not have much interest in exploration -- life is good and they see no reason to shoot rockets up. Assuming light speed is actually an absolute speed limit, combined with a relatively boring solar system that doesn't have much of interest to explore, perhaps without the "exploration" gene they simply don't see the point.
There's not many places to go. Even the closest solar systems are over 6 light years away, which could take over a decade to reach and might not necessarily have any planets capable of sustaining human life. Even if there was, transporting billions of people to another solar system would be an extremely expensive endeavor, and pointless if the Earth is still habitable.
2001 in reverse
"All these worlds are ours, except your one. Do not attempt to leave it"
Solar activity
Their star is less stable than our sun. X-class flares not once a decade, but several times per annum. Too much radiation for humans in space. Electronics lasts a bit better, but not for very long, and only at great added expense.
Also they cracked fibre optic communications earlier in their technological development than we did.
Exotic variant: there is an accretion disk a long way out there bathing their solar system with hard radiation. Their atmosphere blocks it. You'd have to find a way to get rid of the lethal Nitrogen oxides arising from atmospheric ionization, though.
No fossil fuel
Mined out by a previous civilisation, or different plate tectonics. So they went straight to wind and hydro and tidal power, energy storage and solar panels. One can do most things this way, as we are finding out. But rockets are right at the crazy-hard end of that spectrum.
Faster-than-light travel is, according to our current understanding of physics, impossible. That means that if you want FTL travel in your world, then you are free to invent it in any way you want and put any restrictions on it you want.
It might be possible that there is a biological reason why humans do not survive FTL travel, while other species do. Transhumanism might be out of the question, because if humans would use bio-engineering to change the aspect about them which prevents them from FTL travel, they would lose what defines them as human. So that's no solution. That means that they are bound to Earth, and all they can do to project their presence in the rest of the universe is to send automated probes or hire envoys from other species.
If you want to write hard science fiction where FTL travel is impossible and any interstellar travel needs to happen at sublight speed, then the answer to this question writes itself: their lifespan is too short for interstellar travel. As long as humans don't get much older than 100 earth-years, it's impossible to reach any interesting destination within a regular lifespan. But what if this is exceptionally short compared to other species? If the median life expectancy of all other sapient species in the galaxy is several orders of magnitude longer, then spending a couple thousand earth-years of their life traveling through space might not be that much of a deal for them.
Multiple-Star System
They live in a star-system with multiple stars and few other planets.
Thanks to the dance of their several suns, it's always daytime and no member of their race has ever seen a night.
No planets ever cross their sky that they can see.
At most, they are aware of comets and occasional meteorites and have some interesting (and probably very wrong) theories on the subject.
They never invented the science of astronomy.
They never looked up at the moon and wanted to reach it because they don't have one.
The only way they could ever see a star is by flying to their upper atmosphere and shading a long-exposure camera against the suns. Keep in mind that without having any idea there's anything there, they might never try this!
Theirs is a civilisation that lives beneath a bright domed sky and has no conception of anything beyond it at all.
Good question ! imho there will be motivation..
Dreaming to fly, be able to fly
Any long term rule not to fligh, or not to travel in space, will be challenged.
People who have discovered engineering and technology also do science. A scientist will want to fly, to see if it can be done, to see what's up there. Many other people just want to fly.. on Earth, we apes had this dream, for centuries. Very hard to invision high-tech society without that wish. In a few centuries, we succeeded, then we wanted to fly really high. Get into orbit. Or to the moon.
.. but religious constraints took over
Earth has some conservative clergies, suppose they take over again. One of the rules of faith would be: "you can't fly, only God can fly and the heavens is God's Domain and you can't enter it, because if you do, you will always fall and die."
