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Comment by pavel_lishin | Hacker News Reader

> According to Albert Einstein’s general theory of relativity, the behavior of a black hole depends on two numbers: how heavy it is, and how fast it is rotating. And that’s it. Black holes are said to have “no hair” — no features that distinguish them from their fellows with the same mass and spin.

As far as I know, there's a third property that black holes have - electric charge. Would a sufficiently strong electric charge between two black holes be detectable, whether they both have the same charge, or opposing charges?

I suppose based on the article, the effects would only take places once the black holes got within 40km of each other...

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Black holes can have charge but a charged black hole would attract ions of the opposite charge strongly and would quickly neutralize. So it would be quite difficult to get a non-negligible charge on a black hole.

So some very advanced and bored civilization could take black holes and shoot gigantic numbers of protons into it, and get a very positively charged black hole.

If you pump in enough charge that the electrical repulsion is stronger than the gravity attraction, you can then store them safely next to each other, for when you might need one.

It also allows you to move the black hole around, somewhat freely.

It may be a very useful thing if it turns out that we can make small ones.

> move the black hole around, somewhat freely [...] small ones

At the risk of spoiling the mystery of a 50-year-old short story, this happens in the The Borderland of Sol by Larry Niven.

If you enjoy that sort of thing, also read Killing Vector by Charles Sheffield.

I immediately thought of that story as I was reading the comment you replied to :P

Flinging one at an enemy civilization could be a clean way to resolve conflicts!

"Aside from permanently rending the very fabric of space and time itself, there was very little collateral damage."

Well, it's not like it's in short supply...

It is practical? If you don't slow it down somehow it will pass through anything and go away through the other side.

Maybe you can time it to evaporate on your enemy, but that's an incredibly precise timing, and your enemy will literally be able to see it coming and deflect it.

Cool. You would of course end up negatively charged yourself and therefore quite strongly attracted to the black hole.

So I would recommend moving your civilization to a Dyson sphere around the black hole before aiming your cluster of LHCs at it.

Judging by what the article says they can't be different

> In theory, there’s a third defining property: electric charge. But real, astrophysical black holes have negligible net charge.

It has been proposed and is often studied in different contexts, but it seems unlikely that we will be able to measure it any time soon.

I think you might just need a comb and some pieces of paper

Don't forget color charge:

https://arxiv.org/abs/2310.16877

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