# Extracting Info from a Black Hole: Robert's Hypothetical Process

• I
• Creedence
In summary, Robert thinks it's possible to drop a satellite into a black hole and then drop a massive object after it to cause perturbations on the event horizon. He thinks this scenario is self-contradictory because it tries to have the satellite both fall into the singularity and not fall into the singularity.
Creedence
TL;DR Summary
Extract information from a black hole by manipulating the event horizon
I just wandering about the following hypotetical process to get some information from the inside of a black hole.
1. Drop a satellite into the black hole on a nearly tangential orbit.
2. After it crossed the event horizon drop a large mass after it (for example a small black hole).
3. This mass causes perturbations on the event horizon and at a certain part of the satellite's orbit may get outside.

Is it possible? Thanks for the answers,
Robert

No.

No. Crossing an event horizon is forever. It is literally the boundary between places where "somewhere other than the singularity" is included in your future lightcone and places where all routes lead to the singularity. You can certainly manipulate the 3d shape of an event horizon, but that can't change the fate of something already inside the horizon.

Ibix said:
No. Crossing an event horizon is forever.
In a static case. But in the case of two, rapidly moving black holes?
In the case of a rapidly orbiting binary black hole the common event horizon moves very fast. It may move faster than a massive object.

See edited post above.

So saying the satellite crossed the event horizon is another way of saying it will end up in the singularity. Trying to have it escape again, therefore, is trying to have it both fall into the singularity and not fall into the singularity. The scenario is self-contradictory.

Ibix said:
So saying the satellite crossed the event horizon is another way of saying it will end up in the singularity. Trying to have it escape again, therefore, is trying to have it both fall into the singularity and not fall into the singularity. The scenario is self-contradictory.
I think you suppose that the black hole is stationary. But in this case it is perturbed and changing in time. Some points get inside then leave.

Creedence said:
Some points get inside then leave.

No, they don't.

Why are you asking us a question if you don't believe our answers?

No, no, and no. It seems you do not understand the meaning of "event horizon".

Creedence said:
I think you suppose that the black hole is stationary. But in this case it is perturbed and changing in time. Some points get inside then leave.
I am not supposing anything. The event horizon is simply not defined the way you appear to think. It is the boundary between regions of spacetime where you can ever escape and regions where you can never escape. As I already said, the 3d shape of the surface (for some definition of 3d) may change, but it is defined as the surface of a region of spacetime (not just space!) from which you can never escape. If you escape, you weren't in a region where you can't escape. So you weren't under the horizon.

The maths is complicated but the concept here really is simple: there are regions in spacetime (remember this is spacetime, so I am taking into account its dynamical structure) from which you cannot escape. The event horizon is defined as the boundary of these regions. If the evolution of spacetime means that you will be able to escape, you are not in a region from which you cannot escape and you have not crossed the event horizon. If you have crossed the horizon then you are in a region from which you cannot escape (even taking into account the future structure of spacetime) and that's all there is to say.

Creedence said:
Some points get inside then leave.
Just to add - I can see why you think this for a non-axi-symmetric event horizon. But it is wrong. You can certainly define paths that enter and leave a horizon (symmetric or otherwise), but they are not timelike. And the sensible interpretation of "point" in relativity is "timelike line". They cannot leave. Your intuition that they ought to be able to fails you in strongly curved spacetime.

Orodruin said:
No, no, and no. It seems you do not understand the meaning of "event horizon".
I know what is an event horizon (or apparent horizon in this case). My fault was that I assumed that the innermost stable photon orbit is in the EH. Thanks for the answers.

## What is a black hole?

A black hole is a region in space where the gravitational pull is so strong that nothing, including light, can escape from it. It is formed when a massive star collapses in on itself.

## How does Robert's hypothetical process extract information from a black hole?

Robert's process involves using a specially designed spacecraft to enter the black hole and collect information from the singularity at its center. The spacecraft would use advanced technology to withstand the extreme gravitational forces and gather data from the singularity.

## What kind of information can be extracted from a black hole using this process?

Using Robert's process, scientists would be able to gather information about the physical properties of the black hole, such as its mass, spin, and charge. They could also potentially learn more about the nature of space and time near the singularity.

## Is it possible to extract information from a black hole without using Robert's process?

Currently, there is no known way to extract information from a black hole without using Robert's process. The extreme gravitational forces and the event horizon make it difficult for traditional methods of data collection to be effective.

## What are the potential implications of being able to extract information from a black hole?

If successful, Robert's process could greatly advance our understanding of black holes and the laws of physics. It could also lead to new insights about the universe and potentially open up new avenues for scientific research and technological development.

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