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To start with, i know You measure the Kardashev scale from stellar success, but lets say we have a civilization that are vastly advanced compared to us, so they are equivalent to a type 2 civilization.

The question is, could it theoretically be possible to lock an advanced race to a planet beyond technology by changing a lot of factors such as increasing size and density of the planet thus raising the gravity along with increasing the atmosphere to a thickness where the atmospheric drag would with our knowledge of physics be impossible to take off from the planet?

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    $\begingroup$ That depends. What kind of g-forces can this race survive. You could sit them on the surface of a neutron star but they'd be crushed into paste on the surface. How advanced is their tech? Atmospheric drag makes it harder but if they can copy their minds into computers and just need to get a small satellite into orbit to relay then they could probably launch that from a high altitude blimp no matter how thick the atmosphere. $\endgroup$
    – Murphy
    Commented Mar 4, 2016 at 11:54
  • $\begingroup$ 1. If something is crushed in to a paste it is obviously too dense. The advanced tech was equilent to a Type 2/3 civ on the kardashev scale, The task was to leave the planet, not to deploy a satelite. $\endgroup$
    – Magic-Mouse
    Commented Mar 4, 2016 at 12:04
  • $\begingroup$ Again, that depends on what their tech allows to count as leaving the planet. Kardashev scale alone is almost meaningless. Do they have nanotech and uploading of minds like Greg Egans Amalgam? If they do then all they need to launch is a package of nanobots which can build a radio receiver and a base somewhere else. Then they can scan and upload themselves to somewhere outside the prison. $\endgroup$
    – Murphy
    Commented Mar 4, 2016 at 12:28
  • $\begingroup$ A type 2 civilization have by definition left their home planet. $\endgroup$
    – Taemyr
    Commented Mar 4, 2016 at 14:41
  • $\begingroup$ @Taemyr thanks for repeating the first line i wrote. $\endgroup$
    – Magic-Mouse
    Commented Mar 4, 2016 at 16:34

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No. If theoretical physics is your only showstopper, then as long as a body is not a Black Hole, anything can, in principle and given enough energy, escape from its surface.

But even in practice it will be difficult to prevent. There is a lot of room between "black hole" and "easily escapable planet". However, if the advanced civilization only wants to lock the other population rather than outright exterminate it, the parameters you mentioned have to remain in a range that does not kill the population directly, or indirectly by destroying the planet's ecosystem or the population's essential technology base. That does not seem to leave much room to work with, because both have evolved to deal with the current e.g. gravity, not with significantly higher gravity.

Also note that rocketry is not the only way to escape the gravity well: A space elevator, for example, does not care about the density of the atmosphere or the surface gravity, as long as there is a material with sufficient tensile strength available to construct the elevator in the first place.

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  • $\begingroup$ Though, to be fair, you probably need rockets to put the counterweight of the space elevator up there in the first place. Building your way up there would result in a massively unstable structure that was prone to falling down and inflicting massive damage to a large chunk of the planet. $\endgroup$
    – guildsbounty
    Commented Mar 4, 2016 at 19:32
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Remove resources

You need specific resources to build a spaceship able to escape the planet. Removing all fuel or energy source on the planet your prisoner will be unable to escape.

Monitor technology

With spy satellites and any satellite weapon able to damage ground installation from space, you can destroy any spaceship or other means leave the planet before they could be built.

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  • $\begingroup$ a planet without energy sources is frozen and inhabitable (i.e. there will always be some source of energy). Lack of readily available fuels could really hinder any kind of development and all space exploration. $\endgroup$
    – Chieron
    Commented Jul 29, 2016 at 12:51
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By pure physics no, unless it's a black hole then people can always escape.

Even removing raw materials from the planet while a good idea would only be a temporary solution, eventually they would manage to cobble something together that can reach orbit.

If you relax the hard science requirements then in theory if you had a way to modify the curvature of space-time enough you could wrap the solar system containing the planet into a bubble. Essentially it becomes a self contained universe curving back on itself and impossible to leave. You would need to do the whole solar system (so they have a sun) and we know of nothing even theoretical that could allow that to be constructed though.

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There two ways of making a planet inescapable. Assuming the advanced aliens have been removed from space and now are all living on their native planet. For maximum effectiveness both methods can be deployed simultaneously.

Low orbital space around the planet is filled with a high density of objects. This will be old satellites, space junk, derelict space stations, old boosters, disused equipment, and wrecked spacecraft left over from the last galactic war. Once critical density achieved any collision between any two objects will produce debris with a high probability of causing further collisions. This is an ablation cascade or as it is known the Kessler Effect. Once the Kessler cascade has reached a sufficiently high level this will make space travel if not impossible then extremely dangerous and difficult. Certainly for spaceships trying to pass through the planet's orbital space.

The Kessler cascade will have to be keep supplied with additional space junk and debris to maintain a lethal zone around the planet. Otherwise the ablation cascade will dissipate over centuries.

If the planet is home to an advanced sapient species it is safe to assume that it has a strong geomagnetic field. This means the planet will have its own system of Van Allen radiation belts. The second method simply involves increasing the strength of the radiation to a sufficiently high level that any living creature, that is to say, one of the advanced aliens, will be exposed to a fatal dose of radiation when they attempt to escape from their own native planet.

The sapients responsible for trapping the advanced aliens on their own planet, will use a form of star lifting technology to direct an increased solar wind and coronal mass ejections towards the planet. The energetic particles will be trapped by the planet's geomagnetic field where they will oscillate back and forth in the radiation belts.

There are two methods of star lifting technology that could achieve this outcome. They are thermal-driven outflow and the so-called "Huff-n-Puff" technologies. The key to both of them is they use magnetic fields to direct plasma and particles towards the planet.

Together the ablation cascade and stronger radiation belts will help imprison the advanced aliens on their planet. However, just in case the aliens can evade these barriers a fleet of drone spacecraft and warships can be kept in readiness to intercept any escaping spaceships. Local asteroids and moons can be armed with railguns, missile batteries and laser arrays.

The entire system can be run and maintained by an army of Von Neumann constructors. While a typical Von Neumann machine is self-replicating system that will keep on making more copies of itself. The Von Neumann constructors will, yes, more copies of themselves, but they will be programmed to make more of the systems needed to keep the ablation cascade at its full strength by continually adding more objects and material to the debris clouds, and the star lifting systems to further add plasma to the radiation belts. This is in addition to building more drone spaceships and weapons for use against the aliens on the planet.

Together all these systems and lethal physical barriers will make the planet inescapable.

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Surround the planet with anti-matter

First, the planet should have a strong magnetic field of its own or have it artificially increased. Then an external net of magnetic field generators is put around the planet, so that together they contain a cloud of charged anti-particles That will annihilate any object launched from the planet.

The field should be layered so that if a vehicle with its own strong magnetic fields is launched in an attempt to punch through, it will cause layers of matter and anti-matter to come into contact, causing a big enough explosion to destroy the ship or force it into the anti-matter.

While this requires more than just changing the planet's parameters, its failure mode of vaporizing the planet should mean that even a very advanced civilization doesn't have a lot of options to escape, while still allowing somewhat normal conditions on the planet surface.

It may be possible to increase gravity and atmospheric drag to the point where no known thrust system can overcome it, but you would not have anything recognizable left on the planet, defeating the purpose of the locking.

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There is one way that would make it physically impossible for even the most advanced aliens to escape from any planet.

Generate a wormhole by expanding a quantum wormhole until the two mouths of the wormhole are large enough to be separated. Place one mouth in low planetary orbit. The other wormhole mouth is moved beyond the planet where it undergoes further expansion and inflation until is several planetary diameters in diameter. Move this wormhole until it surrounds the planet.

Any spacecraft attempting to leave the planet will encounter the larger wormhole mouth. Because the larger wormhole mouth surrounds the planet it is impossible to leave the planet without passing into it.

The spaceship traverses the wormhole and exist from its other mouth. When the spacecraft leaves the wormhole it emerge from the smaller wormhole mouth in low planetary orbit.

If a spaceship enters the small wormhole mouth it can only emerge from the inner surface of the larger wormhole mouth, but it will exit somewhere several planetary diameters above their planet. Spaceships of the advanced aliens will never be able to access the space beyond the wormhole. Effectively the planet is sitting inside the wormhole with nowhere else to go.

One species of advanced aliens permanently trapped on their planet by the wormhole. Escape is impossible.

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