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There's the general space expansion due to dark energy and it acts in areas that aren't gravitationally bound. There's gravitational distortion of space around massive bodies, which also adds space. Lorentz Contraction would be an effect that "reduces" amount of space along the path of motion of the relativistic observer, but it contracts the entire universe for that observer, not locally.

Meanwhile, there's the concept of Alcubierre drive, where a spacecraft would traverse distances by contracting space in front of it and expanding space behind it, resulting in effective faster-than-light travel.

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What operation / physical effect / influence could make the space to contract in front of it? Expansion is easy, place a large mass, done. But how does one go about locally contracting space?

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  • $\begingroup$ In general, it's not a good idea to rush to accept an answer as soon as one is offered. The answer you've accepted is wrong. There's the general space expansion due to dark energy Not true. See physics.stackexchange.com/questions/402319/… . $\endgroup$
    – user4552
    Apr 26 '18 at 21:14
  • $\begingroup$ @BenCrowell: this question already earned a tumbleweed badge. $\endgroup$
    – SF.
    Apr 26 '18 at 22:30
  • $\begingroup$ A paucity of answers is not a good reason to rush to accept an incorrect answer immediately after it was given. $\endgroup$
    – user4552
    Apr 27 '18 at 17:09
  • $\begingroup$ @BenCrowell: I can always move the 'accepted' mark to a better answer if someone posts it. $\endgroup$
    – SF.
    Apr 27 '18 at 18:51
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You need to create negative mass, that is energy density less then the vacuum has in front of the drive, that will contract space.

That would not work with matter that we know, we would need matter that has the ability to create that kind of vacuum.

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  • $\begingroup$ This sounds wrong to me, unless there's a much more detailed argument that you're not making in detail. GR doesn't say that mass-energy creates contraction, it says that mass-energy creates curvature. Contraction is a more specific interpretation of things like cosmological models, and in those models, there is not a correlation between contraction and the sign of the mass (i.e., an energy condition). For example, in a closed cosmology with a big crunch, you get contraction and then expansion, but there is no exotic matter. $\endgroup$
    – user4552
    Apr 26 '18 at 20:35

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