Talk:Penrose diagram

From Wikipedia, the free encyclopedia

WikiProject Physics This article is within the scope of WikiProject Physics, which collaborates on articles related to physics.
??? This article has not yet received a rating on the assessment scale. [FAQ]
??? This article has not yet received an importance rating within physics.

Help with this template Please rate this article, and then leave comments to explain the ratings and/or to identify its strengths and weaknesses.
To-do list for Penrose diagram: edit · history · watch · refresh

Tasks for expert:

  • explain relation to asymptotic flatness
  • Penrose coordinates: just another kind of coordinate chart (two dimensions are suppressed in the diagram)
  • two metrics, role of "unphysical" metric in tracking energy, etc.
  • derivation and extended discussion of some examples (e.g. Minkowski, Schwarzschild, FRW)
  • illustrations of further examples of Penrose diagrams (Vaidya, Schwarzschild-de Sitter, Reissner-Nördstrom, Kerr)
  • write and link to article on Vaidya thought experiments (see Frolov & Novikov, Black Hole Physics, Kluwer)
  • write and link to article on Bondi radiation formalism
  • write and link to article on black hole interior
  • write and link to article on colliding plane wave (conformal diagrams there are not Penrose diagrams in this sense since points correspond to planar wavefronts, not to nested spheres, but c.f. local isometries with black hole interiors)
  • link to discussion somewhere appropriate of smoothness issues (see arXiv preprints of Dieter Brill)

Thereafter, tasks for anyone who wants to help:

  • replace 45 degrees with slope +/-1
  • spell check,
  • improve diction,
  • make citations and links correspond with WikiProject GTR format

Contents

[edit] Penrose-Carter or Penrose?

I think these are also known as Carter diagrams or Penrose-Carter diagrams. I seem to recall something in the Hawking-Penrose lecture book about the origins of these names. -- Anon.

Certainly the Cambridge maths tripos papers use the term "Penrose-Carter diagram": see http://www.maths.cam.ac.uk/ppa/III/2002/III2002p75.pdf -- Anon, 9 Oct 2004 (UTC)

Correct, they are often called Penrose-Carter diagrams. This might even be preferrable because "Penrose diagram" is also used for a diagram depicting implications among the Petrov types of the Weyl tensor.

I would also add, that since they are more commonly called by only Penrose's name (without "Carter"), it is primarily his diagram, and when both names are used, "Penrose" would logically be put first. (I have only seen "Penrose-Carter" once, and have never seen "Carter-Penrose" before discovering this article) -- Eric B, 28 Dec 2005

My General Relativity lecturer (who did his undergrad at Cambridge) says that only Cambridge calls them "Penrose-Carter diagrams". Everyone else calls them Penrose diagrams, apart from Carter himself who refers to them as "space-time diagrams" apparently! Dazza79 (talk) 12:03, 7 March 2008 (UTC)

[edit] Carter

I added a reference to the original paper by Carter that featured such a diagram. An earlier work by Penrose featured a conformal compactification diagram of some sort, but I don't know whether it was a Carter-Penrose diagram per se, including such features as 45 degree light cones. At any rate, they are very often called Carter-Penrose diagrams. I had never before seen them called Penrose-Carter diagrams in the literature, but that name would also make sense.

At first I thought it might be right to move this article to the new name Carter-Penrose diagram; but on reflection, they are most often called Penrose diagrams, so the current name is appropriate.

Andrew Moylan 15:35, 17 Mar 2005 (UTC)

[edit] Feynman diagrams

Arent these the same as Fynemann diagrams ?

No. A Feynman diagram is an entirely different thing to a Carter-Penrose diagram. Note the correct spelling of Feynman. (I have corrected the spelling within the title of this discussion section.)
Andrew Moylan 05:13, 19 May 2005 (UTC)

[edit] Current version (Dec 18 2005) self-inconsistent

Replace 45 degree lines with lines of slope +/- representing the world sheets of spherical wavefronts. This will then be consistent with points corresponding to nested two-spheres. It might also be a good idea to read the Living Reviews paper before making further changes. Or else leave it to the overburdened experts, although I'd be glad for some well-informed help.---CH 04:35, 19 December 2005 (UTC)

[edit] Merge from Conformal infinity

Someone saw fit to create an article, Conformal infinity, by simply pasting in the abstract from a useful review at the LRR website. That should be deleted, probably by "merging" with this article. Needless to say, this article cites the review, so no need to paste in the abstract!

I would agree with anyone who complains that conformal infinity is a more logical name than Penrose diagram, but because most students will recognize the latter more readily than the former, I reluctantly advocate keeping the name, at least for now.---CH 20:02, 24 December 2005 (UTC)

As Eric B notes (below), conformal infinity is a part of a Penrose diagram. The current Wikipedia article called conformal infinity does not say anything important about the concept of conformal infinity in Penrose diagrams, so I don't think there is any need for, or possibility of, a merge between that page and this one. As someone else noted (above), the Conformal infinity article is just an abstract pasted from a scientific article. I believe the article Conformal infinity should be deleted. Andrew Moylan 13:59, 4 January 2006 (UTC)

[edit] Diagrams and other info

I sat down and made some diagrams from scratch, and added some information on how Penrose coordinates derive and differ from the prior diagrams by Minkowski and Kruskal-Szekeres (i.e. the conformal "crunching"), as well as how the diagrams are used to map black holes. But the rest of those requests I do not know about. Penrose diagrams, from what I have seen, are used primarily for black holes, and some other events in space-time. (I could probably articulate something on "black hole interior" if I had time, but that is probably better covered in the article "black hole".

I had considered doing the merger as well, but I do not understand "conformal infinity" beyond simply its being the distant points on the Penrose diagram. From the article written, there seems to be a lot more to it. Perhaps it should remain a separate article, as it seems to have some meaning on its own outside of Penrose diagrams. -- Eric B 16:30 28 Dec 2005