Talk:Cosmological horizon

How big is a quarter?

Is that what they meant by "Quarter sized"? I was a little confused by that. As for the size... 24.26 mm in diameter.

"In any case, it is interesting to note that the cosmological horizon is a maximal limit of perception and not an actual boundary" ... I'm not sure this is a safe statement: the nature of reality is always relative to an observer. for example, doesn't this in-principle boundary of visibility form an event horizon with an equivalent effect to hawking radiation?Snaxalotl (talk) 03:47, 11 June 2009 (UTC)snaxalotl

Size of the Universe

I would like to see some mention here of the size of the Universe, such as can be found on the observable universe article.

I would also like to know what the difference is between the/a Cosmological Horizon and the/a Particle horizon.

I copied some text over myself from the OU article, but it didn't quite fit so I undid it. Nagualdesign (talk) 04:16, 16 February 2009 (UTC)

Particle horizon ?

Isn't the particle horizon the distance at which are now objects from which we receive the light now, that's to say roughly 50 billion light years, not to confuse particle horizon with Hubble's horizon at 13.7 Gly ? (imagine an object emitting on the Hubble's horizon, the time its light comes to us, it would have moved (faster than light)) —Preceding unsigned comment added by 129.175.69.214 (talk) 08:56, 31 March 2010 (UTC)

Lineweaver and David

The above seems to conflict with the cited article by Lineweaver and Davis. In the case of a positive cosmological constant, an even horizon exists. — Preceding unsigned comment added by 193.29.76.37 (talk • contribs)

Some errors in this article

This article needs a review from an expert. As was stated in another comment, the article by Lineweaver and David points out clearly that the Hubble radius is not an event horizon when the Hubble parameter is not a constant in time (which, in the current accepted cosmological models, it is not). Light emitted from particles at the Hubble radius will still reach us in a finite time. Light emitted from the cosmic event horizon will reach us at infinite time. There is a very subtle difference between the two, but nevertheless an important one. The definitions in the article are partly right, mixed with wrong elements. I am no expert myself, so I will not alter too much. Someone with cosmological authority should. — Preceding unsigned comment added by 78.23.25.41 (talk) 09:04, 13 June 2017 (UTC)

I agree. But I'm a bit hesitant to edit it because I'm not confident enough. But for example, "In an ever-accelerating universe, if two particles are separated by a distance greater than the Hubble radius, they cannot talk to each other from now on (as they are now, not as they have been in the past)" contradicts what is mentioned a bit before that "It is a common misconception that light from the Hubble radius can never reach us. It is true that particles on the Hubble radius recede from us with the speed of light, but the Hubble radius gets larger over time (because the Hubble parameter H gets smaller over time), so light emitted towards us from a particle on the Hubble radius will be inside the Hubble radius some time later." I think the later is true (or at least thought to be true by most scientists according to our current best guest).

Also, this might seem like a detail, but I don't think it's quite right to say that "The particle horizon [...] is the maximum distance from which particles could have traveled to the observer in the age of the universe." Rather, the particle horizon is the current distance at which those particles are, not the distance at which they were when they emitted the photons we're now receiving (if I'm not mistaken). --Mati Roy (talk) 11:27, 16 February 2019 (UTC)

Yeah, this article's a mess. In addition to what was pointed out above, the current definition of "Future horizon" is vague but seems to be synonymous with the event horizon. Maybe it was intended to refer to the far-future limit of the Hubble distance (which is also the limit of the event-horizon distance)? If so, it's very unclear. It would also be good to add values, e.g. 14 Gly for Hubble distance, 16 Gly for event horizon, 17 Gly for "future horizon"(?), 47 Gly for particle horizon. Patallurgist (talk) 08:04, 27 February 2019 (UTC)

"at the same location in space that happened in the distant past"

Links to the 'spacetime' article. What the heck is the point of this link? How does it explain the link text or the rest of the sentence that precedes it? It seems to me this link is spurious and distracting and should be removed. Thanks. Comiscuous (talk) 20:10, 19 April 2021 (UTC)