Bare patch of universe near event horizons?

[Baby Astronaut]

Light is everywhere, it's said. But what about near the other side of an event horizon....wouldn't that have even less of it or anything/particles than the emptiest regions of intergalactic space?

[Sisyphus]

Light is everywhere, it's said. But what about near the other side of an event horizon....wouldn't that have even less of it or anything/particles than the emptiest regions of intergalactic space?

 

What event horizon? You mean near a black hole? Light can enter a black hole, it just can't leave.

[Baby Astronaut]

What event horizon? You mean near a black hole?

Yes.

 

Light can enter a black hole, it just can't leave.

Exactly. And so probably, from within the black hole, the light can't move towards the event horizon again.

 

I'm guessing from within a black hole, nothing can escape its event horizon or move towards it. Once inside the event horizon, anywhere within it, nothing can escape from its position to move towards the event horizon.

 

So logically, it'd seem just inside the event horizon would potentially be clear of "debris" and/or light. Because once something passes any distance towards the black hole's center, it's physically impossible for that something to ever move in the opposite direction -- according to the known laws of physics.

[Sisyphus]

But stuff continues to enter. Rivers only flow in one direction, but they're not empty (otherwise we'd call them valleys).

[Baby Astronaut]

Sure. But my question was...

 

...near the other side of an event horizon....wouldn't that have even less of it or anything/particles than the emptiest regions of intergalactic space?

 

Not empty, but less full than the emptiest regions of deep intergalactic space. For example, let's place the black hole in the most empty regions of intergalactic space. Not much would be rushing in then, giving it a chance to have even less stuff near the horizon -- compared to the other neighboring space around the black hole.

[Spyman]

If the Hawking radiation is correct then the immense gravity from the Black Hole itself would create a 'thermal bath of particles' that continues to enter through the Event Horizon.

 

Hawking radiation (also known as Bekenstein-Hawking radiation) is a thermal radiation with a black body spectrum predicted to be emitted by black holes due to quantum effects.

...

Black holes are sites of immense gravitational attraction. Classically, the gravitation is so powerful that nothing, not even electromagnetic radiation, can escape from the black hole. It is yet unknown how gravity can be incorporated into quantum mechanics, but nevertheless far from the black hole the gravitational effects can be weak enough that calculations can be reliably performed in the framework of quantum field theory in curved spacetime. Hawking showed that quantum effects allow black holes to emit exact black body radiation, which is the average thermal radiation emitted by an idealized thermal source known as a black body. The electromagnetic radiation is as if it were emitted by a black body with a temperature that is inversely proportional to the black hole's mass.

 

Physical insight on the process may be gained by imagining that particle-antiparticle radiation is emitted from just beyond the event horizon. This radiation does not come directly from the black hole itself, but rather is a result of virtual particles being "boosted" by the black hole's gravitation into becoming real particles.

 

A slightly more precise, but still much simplified, view of the process is that vacuum fluctuations cause a particle-antiparticle pair to appear close to the event horizon of a black hole. One of the pair falls into the black hole whilst the other escapes. In order to preserve total energy, the particle that fell into the black hole must have had a negative energy (with respect to an observer far away from the black hole). By this process, the black hole loses mass, and, to an outside observer, it would appear that the black hole has just emitted a particle. In reality, the process is a quantum tunneling effect, whereby particle-antiparticle pairs will form from the vacuum, and one will tunnel outside the event horizon.

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Hawking radiation is required by the Unruh effect and the equivalence principle applied to black hole horizons. Close to the event horizon of a black hole, a local observer must accelerate to keep from falling in. An accelerating observer sees a thermal bath of particles that pop out of the local acceleration horizon, turn around, and free-fall back in. The condition of local thermal equilibrium implies that the consistent extension of this local thermal bath has a finite temperature at infinity, which implies that some of these particles emitted by the horizon are not reabsorbed and become outgoing Hawking radiation.

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Under experimentally achievable conditions for gravitational systems this effect is too small to be observed.

 

http://en.wikipedia.org/wiki/Hawking_radiation

Edited June 16, 2010 by Spyman
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