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Detection of the Electric Charge of a Black Hole

Light cannot escape from a black hole. However light is also interpreted as the carrier of the electromagnetic force. So how can a charged black hole interact via electromagnetism with its environment? Can one see from the outside of a charged black hole, that this black hole is actually charged? Or is this information hidden, because light (and therefore information about the electric charge) cannot escape from the black hole?

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  • $\begingroup$ The field never fell in with the charge that fell in, it was always poking out to infinity. Anyway, when you think of the electromagnetic field as made of photons, the photons travel faster than light and back in time, so there is no paradox in any formulation. This question is certainly a duplicate, but I can't remember of which. $\endgroup$
    – Ron Maimon
    Commented May 30, 2012 at 10:12
  • $\begingroup$ @RonMaimon I always thought photons are travelling at the speed of light. I guess you are talking about virtual photons, aren't you? $\endgroup$
    – asmaier
    Commented May 30, 2012 at 10:55

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What relativity, more precisely causality forbids is the extraction of any information or particles from the black hole interior.

However, to observe the electric charge of a black hole, one doesn't need to extract any information or particles from the interior; equivalently, the virtual particles don't have to be or aren't "ejected" by a point in the interior. For an external observer, a black hole looks like a semi-translucent membrane on which all the information (and charge) is carried.

As far as the external observers' observations go, the black hole interior doesn't exist at all and everything may be explained by the information, charge, and other things distributed over the membrane at the event horizon (or, if you want to feel safer, distributed over the "stretched" horizon which is a tiny distance away from the event horizon on the external side).

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