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I recently stumbled upon a post in /r/scificoncepts which talked about Dark energy prisons. (https://www.reddit.com/r/SciFiConcepts/comments/nd11sd/dark_energy_prisons/)

To increase the expansion of the universe, dark energy must overcome gravity. This is why galactic bodies are getting further and further away from us whilst celestial bodies within our galaxy are not. However, if dark energy can be manipulated by technology, then it can be used to expand a region of space between two objects.

With sufficient power, one could increase the expansion of the universe at a rate faster than the speed of light. This does not affect causality much in the same way as the Alcubierre drive. However, instead of shrinking space, it is using dark energy to expand space. Thereby making it impossible to travel across those distances. Once there is sufficient emptiness between the two objects, the background dark energy would be more than enough to keep the two objects away from one another forever.

The stronger the gravity between two objects, the more dark energy would be needed to overcome it. So, using it within a solar system would just be a waste of energy. However, on an interstellar scale, the gravity could be weak enough to be worth expanding regions of space for your own use.

Dark energy would be utilised to separate two objects from one another. This could either be used against an antagonistic force or as a way to defend oneself against other forces in the universe. Nevertheless, it would be a unique way to isolate civilisations from one another.

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    $\begingroup$ I'm not really sure how we can reality check. Dark energy is a term for forces we simply don't understand. It might not even be energy at all. We do see expansion of the universe for which we use dark energy to explain, which would put other galaxies out of reach, even for light, according to the theory. We have no way of knowing this right now. In addition there's the dark energy manipulative technology, about we can't say anything. A fictional technology based on a theoretical concept, thought up because we don't understand something. Could you elaborate what to reality check? $\endgroup$
    – Trioxidane
    Jun 2 at 11:14
  • $\begingroup$ The universe is already expanding faster than light. See an introductory discussion in the Wikipedia articles on the observable universe and Hubble's law. $\endgroup$
    – AlexP
    Jun 2 at 12:18
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You would be able to imprison an object if you can expend the space-time around that object faster then the object can cross the space-time, (make the expansion faster then the speed of light if you want to be sure).

You can check this by looking at the equations used to describe how dark energy distorts spacetime, while sounding like they might be messy they are practically Pythagoras in space (and Time), this equations is called the Friedmann–Lemaître–Robertson–Walker metric which is $$ ds^2=-c^2dt^2+a(t)^2\left(\frac{dr^2}{1-kr^2}+r^2(d\theta^2+(sin^2\theta) d\phi^2)\right)$$ where $ds$ is a small length is space-time and $dt$, $dr$,$d\theta$ and $d\phi$, are small lengths in time, radius, and angular coordinates, and $k$ describes the curvature of space.

But the key part, is the function $a(t)$ as it scales the distances in space. (The idea of dark energy comes from equations that describe the behaviour of $a(t)$, and they are messy, and they assume that the dark energy is distributed evenly). I don't know if the expansion you need can come directly from dark energy alone, my knowledge of general relativity is insufficient.

But if you have $a(t)$ to depend on position, as well as time, then you could have pockets, where it is growing, which means that in those pockets the distances between objects increases, and if it grows fast enough, then the object can't escape.

The only way an object would be able to escape is if it is an object that contracts space-time, like a warp drive.

Assuming you don't want the people in the prison to die of heat death as all the heat get sucked out of the pocket, then you would need to slowly contract the space-time back together, because when the pocket is expended light will enter it and be streched out until it is practically non-existent (as light with longer wavelengths are lower energy). But when the space time is contracted it "squeezes" the light, to higher wavelengths, which have higher energy and if the energy is high enough you will vaporise anything in the pocket.

In summary expanding space-time can be used to imprison things, but be carful when you let them out.

Hopefully that helps

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