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    • CommentRowNumber1.
    • CommentAuthorUrs
    • CommentTimeDec 7th 2015
    • (edited Dec 7th 2015)

    have created Reissner-Nordström spacetime with some minimum content.

    Nothing non-standard here for the moment, I just wanted the entry to exist in order to be able to point to it. But eventually I’d like to have a linked table that matches extremal black brane solutions to fundamental particles/branes. Not today though.

    • CommentRowNumber2.
    • CommentAuthorDavid_Corfield
    • CommentTimeDec 7th 2015
    • (edited Dec 7th 2015)

    Hmm,

    r ±G2(M±M 24(P 2+Q 2)) r_{\pm} \coloneqq \tfrac{G}{2}\left( M \pm \sqrt{M^2 - 4 (P^2 + Q^2)} \right)

    doesn’t look right as solutions to

    1GMr+GQ 2+P 2r 2=0. 1 - G \frac{M}{r} + G \frac{Q^2 + P^2}{r^2} = 0.

    OK, had there been G 2G^2 in the last term.

    • CommentRowNumber3.
    • CommentAuthorUrs
    • CommentTimeDec 7th 2015

    Right. And it’s worse, if I display powers of the gravitational constant GG at all, I should also display powers of the speed of light. So I am lazy for the moment and put all these units to 1 (“natural units”).

    • CommentRowNumber4.
    • CommentAuthorNikolajK
    • CommentTimeDec 8th 2015
    • (edited Dec 8th 2015)

    Just because you have it of coordinates here: At one point I was searching for emergent physical metrics from Poisson structures in matrix models (I could actually tweak parameters to get the Reissner-Nordström spacetime) and in a small survey I found two very good papers on all the coordinate of the Robertson-Walker’esk metrics

    http://arxiv.org/abs/0704.2788

    http://arxiv.org/abs/0704.3265

    At the end of the papers (p. 21 resp. p.10) you have tables with the metrics. Just in case you happen to stumble upon a reasonable metric one time and you want to check if it’s some simple universe you deal with here.

    • CommentRowNumber5.
    • CommentAuthorUrs
    • CommentTimeDec 8th 2015

    What kind of matrix models were you thinking of?

    By the way, if you feel like adding some more explicit expressions for various spacetimes to the nnLab, please feel invited to do so.

    • CommentRowNumber6.
    • CommentAuthorNikolajK
    • CommentTimeDec 8th 2015
    • (edited Dec 8th 2015)

    I think my Masters advisor is still doing

    http://arxiv.org/abs/1401.2020

    Semiclassically, the commutator of the XX’s is some Possion tensor θ\theta (2.7) and it’s square gives a metric, gθ Tηθg\propto\theta^T\eta\theta (2.10). I was to look for solutions θ\theta of the equations of motion which are also known solutions for gg of the Einstein equations. It was a look at symplectic geometrical concepts in the not so much studied case where a Pseudo-Riemannian metric is also lingering around. The tensor relation θg\theta\sim\sqrt{g} is more ugly if gg has positive and negative components at the same time. An electro-statics like case for the equations of motion of θ\theta made the Reissner-Nördstrom metric pop out. But the thesis looked solely on the metric geometry, and if anything apriori prevents known-gravity-like solutions within the model. Fermionic fields arising/living on that spacetime was not a concern. There is a paper version of the thesis

    http://arxiv.org/abs/1111.2732

    I looked for a Robertson-Walker entry on the nLab for the references, but there wasn’t one. I didn’t make one because I’m not dealing with this atm.

    • CommentRowNumber7.
    • CommentAuthorUrs
    • CommentTimeDec 8th 2015

    So the matrix model you mean is the IKKT matrix model.

    We do have an entry FRW model.

    Hyperlinks on the nForum are coded as

      [link name](url)
    
    • CommentRowNumber8.
    • CommentAuthorUrs
    • CommentTimeSep 8th 2016
    • (edited Sep 8th 2016)

    I have added a commented survey of the literature on interior solutions of RN-spacetimes here (i.e. solutions where the singular point charge/mass is replaced by a finite mass/charge distribution, resolving the BH singularity).

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