# How to uncurve a black hole

How can you uncurve a black hole and thereby get at the stuff inside?

1. The Big Rip as dark energy reaches its zenith at the end of the universe.

2. If curvature is a quantum field that is a superposition of all possible values of curvature then some values of the curvature are low enough so that the interior can interfere with the exterior.

3. If two black holes merge then as the event horizons merge the event horizon of the merging object will for a time be non-spherical and more like a snowman which would allow matter inside to get further away from one of the singularities than the radius of its original event horizon which would allow two observers travelling in different black holes to meet each other.

Are the above correct ? and in what other ways can black holes be uncurved ?

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I will try to address your points, but I will fall short. I will then try to present a simple approach from my own understanding.

1. We've had questions about this before, you can see Will the Big Rip tear black holes apart? The answer is so strange I don't feel confident reproducing it here.
2. I'm not going to try
3. I think it maybe be a little presumptuous to say you know the intermediary shape. According to the equations of general relativity, the event horizon will be disturbed as the BHs come close, not just when they touch. It's true that the event horizon should "bridge" between the two spheres to some degree, but very specific physics will arise due to the rotation of the system. I just want to note that you can expect a very radiating, very non-symmetric, and possibly exotic solution in terms of the actual shape seen. Even a single rotating BH has an ergosphere. The ergosphere of the combined rotating system will experience its own evolution through time and will affect the movement of the event horizons.

I would say that you should look into black hole thermodynamics in order to answer this well. To start with, the rate of Hawking radiation is sensitive to the gravitational potential the radiation has to overcome in order to escape. This can be changed when other bodies are involved. If, for instance, you brought a neutron star into the gravity well of the BH, the Hawking radiation from the BH could leak over onto the star at a rate greater than it would into empty space. The problem is that the neutron star would also have its own temperature and it would radiate into the BH. If it was a sufficiently lower temperature it could increase the rate of the evaporation of the BH via Hawking radiation. As I understand it, no one disputes this point that the rate of Hawking radiation can be increased.

I think your wording of "uncurve" suggests something more dramatic than increasing the rate Hawking radiation. External actors could increase the angular momentum of the BH, but there is a physical limit to that. In other words, it can't be spun apart.

Perhaps you could try to rip it apart with tidal forces - but a short line of logic proves this is probably impossible. To start with, the only thing massive enough to rip apart a BH would be another BH. Then you have two choices, a smaller one or a larger one. The smaller one would have sufficiently large tidal forces, but would just absorb into the one you're trying to break apart! The larger BH would have weaker tidal forces.

Indeed, we reveal a hard reality from the 2nd law of thermodynamics. Entropy favors the creation of fewer and fewer larger black holes because the entropy scales with surface area.

$$S_{\text{BH}} = \frac{kA}{4\ell_{\mathrm{P}}^2}$$

So if you desire to break apart a black hole, the more important question is "where is all that entropy going to go?" This gives us a powerful tool to limit the possibilities for the action... if it can be done at all.

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Maybe black holes are such wonderful devices which are able to roll back the 2nd law of thermodynamics? –  peterh May 8 '14 at 15:17