# A The CC and cosmological event horizon radiation

1. Apr 29, 2017

### friend

There is Hawking radiation associated with black hole event horizons. And there is Unruh radiation associated with horizons produced by acceleration. I've also heard some suggest that there is radiation associated with the cosmological event horizon due to space itself accelerating in its expansion.

My question is would the radiation produced by the cosmological event horizon be equal to the energy of the cosmological constant? It would seem intuitively so, since each point in space is on the cosmological event horizon of some other point in space. If so, is this coincidence? Or is there some necessary relation between the CC and the acceleration of expansion such that it will produce an event horizon with the right area to produce the same radiation energy as the cosmological constant? Thanks.

2. Apr 29, 2017

### friend

3. Apr 29, 2017

### Staff: Mentor

I'm not a cosmologist, but I didn't see anything in the paper that suggests that the cosmological constant and the radiation produced by the cosmological event horizon are related. What exactly in the paper suggests a link between the two?

4. Apr 30, 2017

### strangerep

In general, Killing horizons are associated with emission of thermal radiation at a temperature related to a property of the horizon known as "surface gravity". Some Killing horizons (such as the ordinary light cone in Minkowski space) have zero surface gravity, hence emit no thermal radiation. In contrast, the cosmological Killing horizon in de Sitter space at $r = \sqrt{3/\Lambda}$ emits thermal radiation with temperature proportional to $\sqrt{\Lambda}$.

For more realistic FLRW-like universes, the situation is more complicated, since more than one kind of horizon can exist (e.g., particle horizon, event horizon, apparent horizon, etc). I'm finding the following book quite good (I'm still digesting it) as it contains a lot of relevant information, with a modern perspective. The Gibbons and Hawking paper from 1977 is just an early contribution to this large subject.

V. Faraoni, "Cosmological and Black Hole Apparent Horizons",
Springer Lecture Notes in Physics, 2015, ISBN 978-3-319-19239-0

Last edited: Apr 30, 2017
5. Apr 30, 2017

### Staff: Mentor

I see. Thanks, Strangerep.

6. Apr 30, 2017

### friend

Yes, thank you.