User talk:AlphaNumeric

Hello, and welcome to Wikipedia. Thanks for your contributions to four-tensor and Cauchy surface. You might be interested in Wikipedia:WikiProject Physics to meet other editors interested in physics (myself, I'm mostly into maths).

I'm a bit worried, however, about the statement

"If

D^{+}({\mathcal {S}})\cup {\mathcal {S}}\cup D^{-}({\mathcal {S}})={\mathcal {M}}

, the entire manifold, then

{\mathcal {S}}

is a Cauchy surface"

which you added to Cauchy surface. The condition implies that every non-spacelike, inextensible curve intersects ${\mathcal {S}}$ at least once, but don't you need some other condition to guarantee that there is only one intersection? I mean, ${\mathcal {S}}={\mathcal {M}}$ is not a Cauchy surface, but it does satisfy $D^{+}({\mathcal {S}})\cup {\mathcal {S}}\cup D^{-}({\mathcal {S}})={\mathcal {M}}$ . I'm also puzzled by the last sentence; could you perhaps clarify what you mean here? Finally, please add a reference, e.g. to a standard GR textbook that explains these concepts.

Thanks again for your contributions, and I hope to see more of you.

Cheers,
Jitse Niesen (talk) 14:13, 20 June 2006 (UTC)[reply]

Thanks for your reply. Okay, we'll wait till you're back at uni; there's no need to rush anyway. The lecture notes are not accessible from outside Cambridge, or at least not via the URL you gave. By the way, I didn't write the article originally.

I forgot to say that if you have any questions, you're more than welcome to ask me. -- Jitse Niesen (talk) 03:59, 21 June 2006 (UTC)[reply]

http://people.pwf.cam.ac.uk/gjw33/Lecture%20Notes/Mathematics%20Tripos%20Notes/Part%20III/General%20Relativity%20(III)/Sections%2016~17.pdf is another link to the file, I've put it on my uni webspace. --AlphaNumeric 12:08, 21 June 2006 (UTC)[reply]

Stewart-Walker lemma

Hello. Do you know that you created Stewart-Walker lemma as a completely orphaned article (i.e. no other articles linked to it)? I've added it to the list of physics topics and the list of mathematics articles. (I also did some minor editing to bring it closer to the usual Wikipedia conventions.) When you create an article it's usually a good idea to try to think of which other articles should link to it and create the links. Michael Hardy 22:12, 29 August 2006 (UTC)[reply]