Talk:Absolute horizon

Errors
This article is wrong, or at least very incomplete/oversimplified. For example the Kerr solution has multiple horizons which have different meanings to different observers. This article implies that there is one true horizon, and this is flat-out false. linas 05:56, 13 January 2007 (UTC)
 * I splatted on single-sentance disclaimer: See, however the articles on ergosphere, Cauchy horizon, the Reissner-Nordström solution, photon sphere, Killing horizon and naked singularity; the notion of a horizon in general relativity is subtle, and depends on fine distinctions. as a short-term fix to the problem. linas 01:29, 25 January 2007 (UTC)

The absolute horizon is defined in geometric terms -- it is independent of the state of an observer. That is, if an absolute horizon exists, it will have the "same meaning" to all observers. The Kerr solution does have many Cauchy horizons, because a Cauchy horizon is defined with respect to any Cauchy surface. Is that what you're talking about? There are also Killing and apparent horizons, but those coincide with the absolute (event) horizon of Kerr. Really, the absolute horizon is just one type of horizon, but there really is just one absolute horizon per spacetime (though it may be topologically disconnected, it doesn't depend on the observer). There is, for example, just one surface in Kerr that could possibly be called an absolute horizon. I think the article makes that very clear, and is thus factually correct. --131.215.100.67 16:19, 19 October 2007 (UTC)

What do we know?
In general relativity, an absolute horizon is a type of horizon that defines a hypervolume of spacetime in which events cannot causally reach outside observers.

In general relativity, an absolute horizon is a type of horizon that bounds a hypervolume of spacetime containing a non-zero set of events that cannot causally impact events outside the horizon.

In general relativity, an absolute horizon is a type of horizon that defines a causally null hypervolume. A causally null hypervolume is a hypervolume that contains events that don't causally contribute to any event outside the hypervolume. — Preceding unsigned comment added by 96.227.223.203 (talk) 04:09, 5 September 2023 (UTC)