# Black Hole and the event horizon

• Charlie G
In summary: However, once inside the horizon, all paths lead to the singularity and time cannot be stopped or reversed.In summary, the conversation discusses various questions related to black holes, including how gravitons escape the event horizon, the infinite density and size of black holes, and the process of black holes evaporating. While the concept of time stopping at the event horizon is debated, it is generally agreed that time cannot be stopped or reversed once inside the horizon. The link provided gives a better explanation of gravitons, and the process of Hawking radiation is explained in relation to black holes.
Charlie G
This question may have been asked before becuase it seems like one of the first questions that would be asked after learning of black holes. My question is, how do gravitons escape the event horizon? They must somehow escape, otherwise the black hole could not influence anything with its gravitational pull.

I have a few more questions on black holes.

I have read that black holes have an infinite density, but I have also read that one of the properties of the black hole is its size. By size do they mean the size of the event horizon? Because something with infintie density becomes a point, right? If the density and curvature of spacetime is infinite, then does time stop, like it would if someone were to move at light speed, according to someone outside the event horizon?

And finally, for black holes evaporating, does the quantum process have to happen outside the event horizon? It seems like it has to. The book I'm reading is Stephen Hawking A Brief History of Time, which may be too brief, kinda went to fast over the black holes evaporating. So when the pair of virtual particles is produced, does the process need to happen really close to the black holes event horizon, so that one of the particles will fall into the event horizon?

The last question I'm not really sure of, I have a feeling that I am way off.

Thanks

This link does a better job of explaining gravitons than I could.
http://curious.astro.cornell.edu/question.php?number=264

However, I think I can answer the others. When the size of a black hole is discussed it is generally talking about the event horizon. Inside the event horizon since nothing can escape it doesn't make sense to talk about what's inside. I believe that time does stop at the event horizon.

You seem to have the right idea about Hawking Radiation. Two particles appear, and normally destroy each other and no net gain or loss of energy occurs. When this happens close to a black hole one is pulled into it, and the other escapes, since there is a net gain from this it must come from somewhere, and the black hole loses mass equal to the particle that got away.

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DaleSwanson said:
Inside the event horizon since nothing can escape it doesn't make sense to talk about what's inside. I believe that time does stop at the event horizon.

Not true.
You can jump into the black hole, and time will not stop for you
In fact, you can cross a horizon of a super-massive BH without even noticing it.

Actually DaleSwanson and Dmitry67 are both right. It depends on one's perspective. To a distant observer, time does stop at the horizon. To the falling object, time seems normal.

## 1. 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. This occurs when a massive star dies and its core collapses, creating an incredibly dense and compact object with a powerful gravitational force.

## 2. What is the event horizon of a black hole?

The event horizon is the boundary of a black hole where the escape velocity is equal to the speed of light. Anything that crosses this boundary, including light, is pulled into the black hole and cannot escape.

## 3. What happens at the event horizon?

At the event horizon, the gravitational pull of the black hole is so strong that time and space are severely distorted. This means that time slows down and objects appear to be stretched out as they get closer to the event horizon. Once something crosses the event horizon, it is pulled into the black hole and cannot escape.

## 4. Can we see the event horizon of a black hole?

No, we cannot directly see the event horizon of a black hole because it is completely invisible. We can only observe the effects of the black hole's gravity on surrounding matter and light. However, scientists have recently captured the first image of a black hole's event horizon using a network of telescopes called the Event Horizon Telescope.

## 5. What happens if someone or something falls into a black hole?

If someone or something falls into a black hole, they would experience extreme gravitational forces as they approach the singularity. Time would slow down and they would appear to be stretched out. Eventually, they would cross the event horizon and be pulled into the black hole, where they would be compressed into a single point of infinite density known as the singularity.

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