JamesAndrix comments on Compartmentalization as a passive phenomenon - Less Wrong

44 Post author: Kaj_Sotala 26 March 2010 01:51PM

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Comment author: JamesAndrix 28 March 2010 07:28:27AM 0 points [-]

Hmm, I suppose it's too much handwaving to say it's only a few meters wide and super dense.

Comment author: Jordan 28 March 2010 08:46:11AM 1 point [-]

My rough calculation says that the density would need to be about a million times greater than Earth's, around 10^10 kg/m^3. This is too low to be a neutron star, but too high to be anything else I think. It may very well be impossible in this universe.

That's assuming uniform density though. Of course you could just have a microblackhole with a hard 1-meter-diameter shell encasing it. How you keep the shell centered is ... trickier.

Comment author: SoullessAutomaton 28 March 2010 03:33:02PM *  2 points [-]

Similarly, my quick calculation, given an escape velocity high enough to walk and an object 10 meters in diameter, was about 7 * 10^9. That's roughly the density of electron-degenerate matter; I'm pretty sure nothing will hold together at that density without substantial outside pressure, and since we're excluding gravitational compression here I don't think that's likely.

Keeping a shell positioned would be easy; just put an electric charge on both it and the black hole. Spinning the shell fast enough might be awkward from an engineering standpoint, though.

Comment author: wnoise 28 March 2010 05:39:00PM *  4 points [-]

Keeping a shell positioned would be easy; just put an electric charge on both it and the black hole.

This won't work for spherical shells and uniformly distributed charge for the same reason that a spherical shell has no net gravitational force on anything inside it. You'll need active counterbalancing.

Comment author: SoullessAutomaton 28 March 2010 07:10:40PM 4 points [-]

Ah, true, I didn't think of that, or rather didn't think to generalize the gravitational case.

Amusingly, that makes a nice demonstration of the topic of the post, thus bringing us full circle.

Comment author: Baughn 28 March 2010 01:26:28PM 0 points [-]

Would it be possible to keep the black hole charged (use an electron gun), then manipulate electric fields to keep it centered? I don't know enough physics to tell.

Comment author: wnoise 28 March 2010 05:41:28PM 1 point [-]

Yes, this could work.