# A piece of a black hole on earth

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What would happen if a 1kg piece of black hole was suddenly transported to the surface of the earth?

Would it retain the properties of a black hole and begin devouring mass that it came close to, sinking into the surface of the earth?

Would it expand to something much less dense since it did not have the gravity of the entire black hole to keep it in that dense state? If so, what type of matter would it be?

Something else?

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Nothing. 1 kg of mass = 1 kg of mass. The effect would therefore be comparable to a package of sugar.

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It would be so small it wouldn't be able to suck anything up even if it had the necessary gravitational pull. It would have so little mass, it wouldn't be able to suck anything. So, nothing would happen. You probably wouldn't even know it happened.

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I am not sure what you mean by a piece of black hole.

Anyway, based on a nieve calculation using the Stefan–Boltzmann-Schwarzschild-Hawking power law the lifetime of a 1 kg black hole is of the order $10^{-17}$ seconds. It would disappear in a flash of radiation.

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Fuzzwood:

So it would stay that same small size? The gravity of the entire black hole is not necessary to keep it that small?

And if it had that mass in a very small space, it could not get close enough to, say, a molecule of hydrogen to pull in that molecule?

I am not sure what you mean by a piece of black hole.

Anyway, based on a nieve calculation using the Stefan–Boltzmann-Schwarzschild-Hawking power law the lifetime of a 1 kg black hole is of the order $10^{-17}$ seconds. It would disappear in a flash of radiation.

I think this answers my question. I was wondering if once matter is compressed to the density of a black hole, does that matter retain the properties of a black hole if the massive gravity is removed. That is, can the mass of 1kg stay in that compressed state without the entire gravity of a black hole to keep it that way.

Edited by zapatos
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I think this answers my question. I was wondering if once matter is compressed to the density of a black hole, does that matter retain the properties of a black hole if the massive gravity is removed. That is, can the mass of 1kg stay in that compressed state without the entire gravity of a black hole to keep it that way.

All black holes (apparently) radiate energy (lose mass). No matter how big the black hole is, it will eventually radiate all of its energy away (unless it is fed more mass than the energy it radiates away) and fizzle out. A small Black hole isn't any less capable of retaining its properties than a large black hole, it just has a shorter life. As it happens, you have picked a virtually infinitesimally small mass (1kg) for a black hole, so it would have an extremely short life.

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• 4 weeks later...

So it would stay that same small size? The gravity of the entire black hole is not necessary to keep it that small?

These are guesses based on a limited understanding of general relativity:

It would not be observed to be the same size. Yes, the entire mass of a black hole keeps everything in it small, not just (or at all?) because it compresses matter against other matter, but because it curves space and length-contracts everything (the size of any matter and the empty space between it).

Using the bag of sugar as a prototypical 1kg, let's just say that you're inside the black hole next to this bag of sugar, and then you and the sugar are transported to Earth. You would experience the same change in observed lengths as the bag of sugar, so from that point of view the size would not appear to change.

How is it conceivable to be in a black hole next to a bag of sugar? If space is contracted so much that what we see as a "small" black hole has length contraction so severe that the bag of sugar and you are infinitesimally small, then the infinitesimal space between you and it can fit comfortably in the black hole along with rooms or planets or an entire universe, making it seem like the inside of the black hole is mostly empty space.

The way to figure out what you'd expect to see is through math, and I don't know black hole math. I may be way off on what the math says, and I may be way off on the interpretation.

Edited by md65536
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The way to figure out what you'd expect to see is through math, and I don't know black hole math. I may be way off on what the math says, and I may be way off on the interpretation.

If we examine the space-time around a black hole it is the same as a space time around a spherical mass like a star (of a spherical bag of sugar in isolation!). So provided we are not very near the horizon of a black hole we would not really care if we had a black hole or a spherical mass, at least as far as the classical geometry is concerned.

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Would it even be possible to get a 1kg black hole, let alone transport it to Earth for it to be annihilated?

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Would it even be possible to get a 1kg black hole, let alone transport it to Earth for it to be annihilated?

Current theory suggests that such a black hole would be smaller than a proton, and evaporate within a fraction of a second. However, it would probably be necessary to understand quantum-compatible gravity to know for sure.

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What if the 1kg object was only slightly larger than its schwarzschild radius? Would it still generate Hawking radiation or would it remain a stable 1kg?

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What if the 1kg object was only slightly larger than its schwarzschild radius? Would it still generate Hawking radiation or would it remain a stable 1kg?

If it was really only just over the Schwarzchild radius then quantum fluctuations would have to be taken into account. No idea exactly how you would do this.

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If it didn't evaporate (if say, the Hawking radiation didn't happen for some reason), it would be very damaging. Things that fell into it wouldn't come out, so it would slowly grow, and the bigger it got the more gravitational attraction it would have. Eventually it would eat the Earth.

The argument that it would only have the same gravitational attraction as a bag of sugar (which is correct) and therefore not do much damage (incorrect) is only relevant if the black hole is near the Earth for a short time (e.g. created with a large momentum).

Of course, as ajb says, it would just evaporate, so no worries.

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If it was really only just over the Schwarzchild radius then quantum fluctuations would have to be taken into account. No idea exactly how you would do this.

Idk but 1kg in the size of a needlepoint or actually much smaller (right?) would have an extreme amount of kg/cm^2, so even if it would move very slowly I would expect it to have a powerful ability to penetrate anything and everything. I guess if it was small enough, it could just go through your body without you feeling much or noticing much of the damage. It would be like getting pricked with an extremely small gage needle, I would think. You might just notice the slightest pinch and a small blood spot. Of course, what happens when it goes through your bones?

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