Talk:Fubini–Study metric

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Error in n=1 formula?[edit]

In the formula

{\frac {dz\;d{\overline {z}}}{\left(1+z^{2}\right)\left(1+{\overline {z}}^{2}\right)}}={\frac {dx^{2}+dy^{2}}{\left(1+r^{2}\right)^{2}}}

shouldn't the denominator on the left be $(1+z{\bar {z}})^{2}$ ? Then it matches up with the one on the right, which is correct, I think. Joshua R. Davis 01:17, 3 May 2007 (UTC)[reply]

Separate articles?[edit]

I suggest creating a separate article for the "Articulation" section, which discusses the Fubini-Study metric in quantum mechanics. For a math article, all the discussion with bra/ket notation seems out of place. Also, much more should be written on the math side, including how the Fubini-Study metric arises as a submersion of the 2n+1 sphere, its sectional curvatures, etc. Jjauregui (talk) 19:25, 14 April 2008 (UTC)[reply]

Conformal to Sphere, not equal[edit]

When I do the transformations specified in the article in the n=1 case, I get

g={\frac {1}{4}}(d\theta ^{2}+\sin ^{2}\phi d\phi ^{2})

Meaning this metric is conformal to the metric of $\mathbb {S} ^{2}$ , not equal. We need to provide the diffeomorphism associated with this invariance (making them conformally isomorphic) if there is one.

I changed the article to include this suggestion; please check and change if I am incorrect. User:Adama4418:22, 14 January 2009 (UTC)[reply]

See my edit summary. First of all,

\mathbf {CP} ^{1}

is definitely diffeomorphic to

S^{2}

. Secondly, the Fubini-Study metric as defined here comes in with a somewhat unconventional normalization. It is important at some point to indicate that there is this ambiguity. Thirdly, because of the aforementioned diffeomorphism (or even homeomorphism) of

\mathbf {CP} ^{1}

with

S^{2}

, both have trivial fundamental group, and so there is no way that

\mathbf {CP} ^{1}

is ever going to be a non-trivial covering space of

S^{2}

. siℓℓy rabbit (talk) 00:12, 17 January 2009 (UTC)[reply]

Rewrite[edit]

The focus on quantum mechanics is totally inappropriate for an article on a standard construction in differential and algebraic geometry. The article should take a mainstream approach to the topic, and then possibly indicate the importance of the Fubini-Study metric in physics and other areas. Furthermore, the use of the bra-ket notation is totally gratuitous and confusing. siℓℓy rabbit (talk) 00:19, 17 January 2009 (UTC)[reply]

Rewrite, 1st Step[edit]

I've just added what I believe to be an appropriate (mathematical) introduction section which incorporates the local-coordinate material from previous versions and sets the reader up for the physics examples and implications which follow. The old "Articulation" section has been renamed "In quantum mechanics and algebraic geometry." That section, I think, still requires a rewrite - but I am not a specialist in those subfields. Matthematician (talk) 17:46, 27 February 2009 (UTC)[reply]

Nice work. Now there's something helpful in WP on Fubini-Study. Digging out the original texts was getting laborious for me. Thank you for making us modern. I hope the applications section, quantum mechanics and algebraic geometry, attract similar efforts. If someone finds them sorely lacking they can place a re-write tag there. For now I've removed the tag at article head. BTW, the edit log credits computer # 24.25.165.169 in Lewiston, Maine, so we only know that it is Matthematician because of the note here in Talk.Rgdboer (talk) 21:31, 27 February 2009 (UTC)[reply]