When a black hole moves, we can sense it with respect to surrounding light. As it moves along, we know that whatever lies behind, has moved from this direction to that direction.

Can this be counted as information escaping the black hole about its own position.

Actually, it is similar to gravity escaping black hole. Because surrounding light is absorbed/bent by gravity only.

In any case, we know that the motor behind event horizon has changed position.

How it is not escape of information from behind the EH about its own position?

  • 1
    $\begingroup$ What do you mean by "information escaping"? Why should the information about the black hole's position be "trapped" in the first place? With sufficiently good instruments, you could infer its position also from the geometry around it (assuming a Schwarzschild geometry you don't need many data points to infer the position, for instance). The "information" people talk about in the context of black holes is usually that associated with objects that fall into them or the radiation they give off. $\endgroup$ – ACuriousMind Jan 14 '17 at 16:12
  • $\begingroup$ I agree if the influence of "what lies beneath EH" on geometry of "outside the EH" is not considered escape of information from/through EH. This influence would be influenced by the objects that fall into them. Therefore, I understand that it is not possible to send out information in the forms other than gravity (geometry). $\endgroup$ – kpv Jan 14 '17 at 17:00
  • $\begingroup$ @ACuriousMind: Actually where I am going with this is - if geometry/curvature information can reach outside EH, then why we say that gravitational waves can not reach outside EH? GW are nothing but variation in geometry/curvature? Your expert thoughts please. $\endgroup$ – kpv Jan 14 '17 at 23:53
  • $\begingroup$ @ACuriousMind: One more question - the good instruments you mentioned, using them alone, can you also infer whether the gepmetry/curvature is caused by a BH or an equivalent mass? I think to tell it is a moving black hole, you may need little more than geometric information, and that would be a visual of EH wrt surrounding light. Am I missing something? $\endgroup$ – kpv Jan 15 '17 at 0:08
  • $\begingroup$ @ACuriousMind: If you comment, then can you follow through with the counter comments? Many times I have seen you make one comment then go silent. Let me ask you again - the geometry information is there due to the presence of mass, therefore it does propagate somehow from where the mass is, to whereever you measure the geometry with your instruments. Is this correct? Secondly, can measuring geometry can distinguish it is caused by a BH, or an equivalent mass? $\endgroup$ – kpv Jan 17 '17 at 15:43

It sounds like your question could be rephrased "Does the motion of the center of mass of a black hole count as information escaping from the black hole?"

No. Aside from the position and velocity, the parameters that characterize a black hole are mass, spin, and charge. These can be measured from outside because they affect the curvature of space-time.

Information escaping means learning any other information about the matter inside through direct measurement.

There is a related topic. Can matter or energy escape, once inside. Sort of. Hawking radiation does reduce the mass, but it isn't exactly mass escaping.

  • $\begingroup$ I agree that information can not be sent out in any other form than curvature of space itself. And curvature of space can convey at least mass, velocity, and may be spin. But the fact is that this information is conveyed by the center mass and its motion. If the geometrical/curvature effects do reach out to outside world, then gravitational waves are also variation in geometry/curvature effects. Next question would be - why we would think that GW can not escape EH? GW are nothing more than variation in geometry/curvature. $\endgroup$ – kpv Jan 14 '17 at 23:39

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.