B What Happens at the Event Horizon of a Black Hole?

[Steve1954]

At the event horizon of a black hole, the curvature of space is infinite. Matter falling in therefore becomes accelerated to the speed of light. General relativity says infinite energy need to accelerate mass to the speed of light. Comments please

 

[Orodruin]

At the event horizon of a black hole, the curvature of space is infinite.

No it is not.

Matter falling in therefore becomes accelerated to the speed of light.

No it is not. You need to be careful with what you mean by this. The event horizon locally moves at the speed of light, but this is because it is a null surface. It is the event horizon that locally moves at the speed of light relative to all observers. Any observers will have a relative speed below the speed of light.

 

[Vanadium 50]

Comments please

OK, here's one. Not a single thing you said was correct.

Here's another one. Posting a parade of incorrect statements is an inefficient way to learn.

 

[Ibix]

At the event horizon of a black hole, the curvature of space is infinite.

As noted by Orodruin, no it is not. Curvature goes to infinity at the singularity, not the event horizon.

Matter falling in therefore becomes accelerated to the speed of light.

This isn't correct. The event horizon is an outgoing null surface, so a local description of a horizon crossing is that the horizon crosses you at the speed of light. But this doesn't mean you are doing the speed of light anymore than the fact that light passes you at the speed of light means you are doing the speed of light.

"Speed" in curved spacetime is not simple. Our everyday intuitive notions of it generally rely on assumptions that are spectacularly invalid near black holes.

General relativity says infinite energy need to accelerate mass to the speed of light.

Although you see this in a lot of popsci sources, it's quite misleading phrased this way. It's better to say that it's impossible to describe something with mass traveling at the speed of light in a coherent way. The "infinite energy" comes from trying to apply the formula for kinetic energy of a massive body to a situation where it is not valid.

 

[timmdeeg]

General relativity says infinite energy need to accelerate mass to the speed of light. Comments please

You seem to mean proper acceleration here, e.g. acceleration by a rocket. But in the context you are mentioning objects are passing the event horizon in free fall.

 

[PeterDonis]

Comments please

As has already been pointed out, every statement you made is incorrect. And you didn't ask a question, so there's no point in continuing this thread.

Thread closed.