# Event Horizon

1. Dec 4, 2005

### benzun_1999

hi,
i was just wondering as the mass of the blackhole keeps increasing due to increased mass getting deposited on it does its event horizon increase
because of this?

does the blackhole have infinite density?

-Benzun

2. Dec 4, 2005

### Vast

Certainly does. And the yes, the spacetime inside a black hole is said to have infinite curvature and matter squeezed into infinite density.

3. Dec 4, 2005

### ek

The "core" of a black hole is infinitely small and infinitely dense. But it does have a relatively "fixed" mass, that is to say that the mass is not infinite one way or the other, such as the volume or density.

4. Dec 24, 2005

### benzun_1999

if infinite density exists wont its gravitationl potential be also infinite. So its evvent horizon would cover the entire space time.

-benzun

5. Dec 25, 2005

### Chronos

I still vote for the planck density as the upper limit.

6. Dec 25, 2005

### Vast

No, its gravitational potential is not infinite. A black hole is no different to any other celestial object one encounters in space. If a black hole has a mass of 15 solar masses, then objects gravitate around the black hole in the same manner as if they were orbiting a 15 solar mass star.

The second part about its event horizon, is all to do with escape velocity. Earth has an escape velocity of 11 kilometers a second, a black hole has an escape velocity of 300,000 kilometers a second which is also the speed of light, hence light cannot escape. Everything has an event horizon if it is compressed small enough, even the Earth has one if we were to shrink it into about the size of an atom.

Correction, the Earth would have a Schwarzschild radius of half a centimeter. (That’s the distance from the singularity in the center to its event horizon)

Last edited: Dec 25, 2005
7. Dec 27, 2005

### benzun_1999

so i believe i am correct in telling that infinite density is not possible. there is a maximum density for anything in spacetime. i am kind of working on a theory like this. i dont know how to procced i will be really happy if anyone helps me. if interested pls pm me.

8. Dec 27, 2005

### Vast

Well until we have a theory of quantum gravity, we aren’t really sure what happens inside a black hole, especially at the singularity. There’s nothing (AFAIK) in relativity to say infinite density is impossible. So if the planck conditions are reached inside a black hole, it will be limited by quantum gravity to about 10^94 grams per cubic centimeter.

9. Dec 27, 2005

### Garth

If the idea of infinite density, or alternatively a finite mass body collapsing down to a singularity of zero volume, seems impossible and unphysical, then ask: "What is it that prevents ordinary objects from not having zero volume? What gives objects in the physical world its geometrical structure?"

The answer is of course the strong nuclear and electro-weak forces. What happens then when the gravitational force inside an event horizon overcomes all other possible forces? What is it that prevents such a collapsing object from not collapsing to zero volume and infinite density?

Other forces stronger still will be required, so far we do not have the physics to deliver such strong replusive forces, yet.

Garth

10. Dec 29, 2005

### Chronos

I would vote for the uncertainty principle. It insists all entities occupy a finite, albeit incredibly tiny volume - which works out to be the planck density.