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DISCLAIMER: This question is for a game, so any answers should assume that the person/people will attempt to go to the surface, even if they know it would result in certain death.

If there was a human civilization living under ground, why would the inhabitants not be physically able to reach the surface? The issue I have with this question is that it is very straight forward to prevent a human from descending further underground (as I found from my previous question), but I can't think of any reason why ascending would be impossible. The circumstances don't have to be relevant to the Earth, so a hurdle that occurs on an alien planet is allowed (to a point), but the technology is mostly of our time (don't ask how they got there)

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Ben Hollier
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    You're saying "not be able to physically reach the surface", do you mean they literally can't get there or just can't get there and continue to live? – Samuel Apr 29 '15 at 17:34
  • I've voted to close. After seeing just a few of the answers to this question it's clear that, as written, it is either too broad or off-topic because is about idea generation. – Samuel Apr 29 '15 at 18:02
  • @Samuel (As a response to the first comment) I'd prefer literally not being able, because it means less work on my end (game assets etc.) but either would suffice. And also, sorry about the open-ended-ness of the question, but I had a complete brain block when thinking of anything – Ben Hollier Apr 29 '15 at 18:33
  • Ok, I've updated my answer. – Samuel Apr 29 '15 at 18:49
  • Those two options give very different moods and will lead to very different adventures, especially if the PCs are going to be quixotic. – Beta Apr 29 '15 at 20:34
  • There are beastman on the surface inside of giant robots killing everybody who gets to the surface. I hope someone gets the reference :) – Vajura Apr 30 '15 at 06:15
  • In an article extracted from xkcd what if the Earth stop spinning the wind on the surface will be blowing at break neck speed... – user6760 Apr 30 '15 at 07:57
  • It is peculiar that questions deemed close-worthy have also been deemed up vote-worthy. – Jax Apr 30 '15 at 15:20

10 Answers10

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Simple. Several options are available to you:

The I'll get there but die after stuff

You have a situation where the surface is so full of radioactive materials (possibly a byproduct of nuclear war?) that everyone had to migrate downwards in order to avoid radiation. If anyone goes up, they die of radiation poisoning.

You have a "surface" that's always stormy, with ludicrously high winds and flying debris all the damn time. Walking outside? Not a chance, you'd get blown away and ripped apart between storms.

More insane? What about if your planet was in a system where there your planet was prone to being hit by asteroids? Being on the surface means you'd get hit by one or two falling rocks at least several times a day - good luck surviving that.

How about considering an atmosphere-less planet? Your people have terraformed the inside of a big rock to live there, but because the rock wasn't big enough to sustain an external atmosphere, you've elected to seal an internal atmosphere inside your cave system. Anyone breaching the surface will kill everyone in the rock unless the hole is sealed, and if you walk outside the air in your lungs will kill you.

Consider the opposite of the above. What about an atmosphere that doesn't have oxygen in it? Perhaps it's a CO2 atmosphere. Walking outside = suffocation.

Those are some of the environmental possibilities, but what if the surface of your planet was uninhabitable because of predators? Perhaps you've got a human hunting race that lives on the surface, and going outside = being hunted.

Of course, if you prefer the "literally can't reach the surface" stuff

From a more generic perspective: your world contains an element that is so hard that you can't break it. Cover the surface with it.

Lets step into Crazyland for a second. Let's say for a second that the planet was encompassed by something "alive" - perhaps a really really fast growing plant. The ceiling you think is stone/rock/dirt/whatever is really actually that plant, which happens to (for whatever reason) grow in the shape of a hollow sphere. Trying to dig through this plant would result in instant regrowth, and you'd probably lose your tools trying to do it. Enough of Crazyland, lets get out.

Alternatively, have creatures that live near the surface but still underground, but not deep enough to harass your citizens (Giant man eating worms that don't like warmth, perhaps). They're advanced creatures, and can detect vibrations in the earth. Once a digger gets above a certain depth, they go straight for his sorry arse and he makes a nice meal for said creature.

Aify
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  • None of these prevent people from reaching the surface, they only kill people once they get there. – Samuel Apr 29 '15 at 18:51
  • I know, but I elected to answer based on the disclaimer since it's nice big and bolded. After all, it does say they'll try (but says nothing about failing) and it has to result in certain death... so they can try all my methods and succeed, resulting in certain death. @samuel – Aify Apr 29 '15 at 19:00
  • I read that as they die in the attempt to get to the surface, not that they would die after getting there successfully. – Samuel Apr 29 '15 at 19:06
  • For the toxic atmosphere case, the atmosphere might become toxic at, say, 100 m and above, preventing people from reaching the surface. Alternatively, there might be no atmosphere on the surface, only a small amount of air collects in the tunnels. That way the pressure is too low to continue even before you reach the surface. However, both methods could be defeated by simple breathing apparatus. – 2012rcampion Apr 29 '15 at 19:13
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    Well, with regards to the comment from OP regarding either literally unable to reach or reaching and dying being okay, my answer is definitely valid. – Aify Apr 29 '15 at 19:20
  • Variation on the radiation issue: the ozone layer is destroyed, too many high-energetic particles reach the earth surface to be safe. –  Apr 30 '15 at 07:50
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As you're designing the game world then you have the ability to make it literally impossible to get there. Most games would simply leave it at that. This is understood by the players, outside the world is abyss, going outside means annihilation.

There are a plethora of reasons that can be given for this.

  • The rock above a certain depth is harder than any man-made tool, it can't be dug through. The surface is awash in solar storms, electronics nearing the surface fail, the high temperature makes machines seize up, the low oxygen doesn't allow motors to operate. The only way through it digging with hand tools and they only break.

  • Magma lies between them and the surface, digging upward simple burrows into hotter and hotter stone until hot death comes, slowing and unstoppably, pouring in from above.

  • A massive cavern lies between them and the surface, the ceiling lost in darkness, no visible way up can be seen.

Mix and match as required. From a game design perspective the empty abyss or solid rock would be easiest to implement.

Samuel
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Extreme cold

The outside of the planet is entirely frozen over - survival is only possible with the heat from the core. Heading upwards, you start freezing and running into ice, and it's next to impossible to reach the actual surface. Maybe a well-funded expedition with good heating/insulation tech could do it.

Dan Smolinske
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  • It won't take much to protect the expedition until it's just below the surface. Just look at what happens with even shallow caves--they keep the same temperature year-round because the heat/cool simply doesn't penetrate. If the surface is ultra-cold the ground will be dry--you'll need to provide enough heat to warm up the terrain close to your tunnel but that's about it. – Loren Pechtel Apr 30 '15 at 01:54
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The surface has been liquified.

Something turned the surface of your planet into molten rock. Perhaps giant a giant space battle culminated with space ships using lasers to melt the surface. Perhaps the planet just has a very eccentric orbit where the surface gets seasonally melted by the star.

Whatever the case may be, on this planet, human life can only exist within a habitable zone between the molten surface and the molten core. Any attempt to dig to the surface will result in the digger either succumbing to the heat long before reaching it or else with molten lava flooding their tunnel. Either way, fatality ensues.

ckersch
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  • The core and the surface would transfer their heat to the in-between zone until it reaches equilibrium. – user253751 Apr 30 '15 at 00:45
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    @immibis : How long would that take? If many hundreds or thousands of years, then the setting can be used. The cataclysm might have happened just recently for the characters currently alive it's not an issue what will happen in a thousand years. – vsz Apr 30 '15 at 06:13
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Perhaps the surface of the planet is a frozen wasteland (think -100F) and an underground colony is warm due to geothermal energy. Anyone venturing outside would freeze to death quickly.

You can adjust the temperature of the surface to speed up or slow down the death.

Kenny
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You could do this (technologically speaking, of course) today. Dwelling underground on Mars is a smart way to have a lock on pressure, contain air, and protect from the harmful effects of radiation. Most certainly, anyone that breaches the surface will die, and maybe take others with her.

You already have your solutions for sustaining the population underground, so I won't get into that.

Mikey
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Let's go with the idea that reaching the surface is physically impossible.

  1. Really really hard layer of rock. Say, diamond. Basically impossible to drill through, and likely to continue for a long distance.

  2. Too far from the power source. Your underground civilisation might use geothermal power or something, and lack good power storage. Which means that further up from the magma layer, you don't have the power for digging, or even keeping people alive.

  3. Weird physics. Be inventive here: physical anomalies could be things like for example gravity that switches direction randomly, making it impossible to figure out which way is up. Or time dilation effects.

  4. Evil bad guys in the way.

Fhnuzoag
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Underground is a now inactive volcanic cavern, only entrance to the surface is a single lava tube about 250 feet long. Your people have really free movement down this tube and start to colonize the underground, bringing people and resources down as they need.

One fateful day, over 50 miles away, a flood event triggers a landslide and reroutes an entire river towards our hapless underground dwellers. The new route this river takes leads it towards the lava tube...river splits, part staying above ground and part rushing down this lava tube opening to the underground. River flows underground and ends up flowing through a series of smaller tunnels (not big enough for a human to fit) and eventually rejoins the rest of the river.

You now have people that once had free access to move whatever they wanted underground, but a single event cut them off with no ability to return to the surface without braving a 250 foot tunnel with extremely fast rushing water flowing through it. As a last irony, this river is the underground populations only fresh water, giving them life and at the same time trapping them.

Edit to add: Cavern is former volcanic lava pool...while the lava that solidified might be easier to dig through, the granite that held the lava in the pool is not and requires dynamite to get through, which would risk the entire underground area with collapses.

Twelfth
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A black hole has devoured one of the stars in the system and been captured in the process--and the radiation jet from the black hole is bathing the surface. (Since it's a binary system the black hole has a lot to feed on and thus the jet will be very powerful.) Once you get within a few feet of the surface you fry in the radiation and die before you can dig through the last distance (which has become fused to solid rock so people aren't going to break through in the short time before they die.)

This provides a lethal near-surface environment without the heat problems that a lava surface entails. It's also extremely difficult to shield against that level of radiation.

Loren Pechtel
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  • Loss of enough ozone would trigger a "lethal near-surface environment", eventually. When it's 200 degrees outside, you cannot go. – Mazura Apr 30 '15 at 03:15
  • @Mazura Losing the ozone layer won't change the outside temperature and it only means extra UV--which won't penetrate the ground. Thinning the atmosphere would make for more temperature variation but it will average out, protecting a digging team until breakthrough would be easy. He's not looking for a lethal surface, he's looking for something that will keep people from even reaching the surface. – Loren Pechtel Apr 30 '15 at 03:56
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There is a sci-fi novel written in the 1980's about such a setting. The surface could theoretically be reached, but from the point of view of the inhabitants it is impossible to get there, actually they have been living underground for so long that the surface became a mythical place.

The whole society was designed to be a utopia to last almost forever (which worked for some time, but in the time the novel is set, it is slowly falling apart), and the status quo is upheld by a very authoritarian regime (masquerading as a very democratic one, just like a "Democratic People's Republic")

No one is allowed to believe in being able to reach the surface, and if someone is crazy enough to even think about trying it, they will be quickly arrested.

In fact, there might have indeed been a cataclysm which made the surface inhospitable but it's long over, and the surface is now inhabitable. The people are just kept in darkness, to sustain the regime.

I don't know of any English translation, the title might be roughly translated as "The ones living in a cocoon".

This is an example where returning is impossible, and not that the surface would just be dangerous. If you told someone "let's dig upwards so we can reach the surface" they would react as if you told in real life "let's steal an airliner and fly high enough to reach Heaven.". If you tried to act (steal equipment and dig), you would be arrested as an enemy of society, and either "re-educated" or disposed of.

vsz
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  • I removed the edit about "The City of Ember", because it is nothing like that. If you think it would be a suitable example, please write in a comment or an answer. – vsz Apr 30 '15 at 15:07