Recent content by Chris Hillman

BRS: I'd rather be yakking about Kleinian geometry! Re www.physicsforums.com/showthread.php?t=462413 Such a project would be much too hard for an undergraduate. But looking towards graduate work, he should make sure to learn about symplectic integrators for Newtonian multibody...

BRS: Kleinian Geometry, anyone? ... No? ... Sigh ... Re "Mapping Class Group and Path-Component of Id" www.physicsforums.com/showthread.php?t=460570 quasar misunderstood the question, I think. The identity component of a (nontrivial) topological group G is the connected component of...

BRS: Conformal Compactifcations of Spacetimes. II. Minkowski Vacuum cont'd I should say a bit more about null geodesic congruences in Minkowski vacuum, as represented in the Penrose conformally compactified chart ds^2 = \frac{-dT^2 + dR^2 + \sin(R)^2 \, d\Omega^2} {(\cos(T)+\cos(R))^2}, \...

BRS: Why do first covariant derivatives of the metric tensor vanish? Again re "Metric tensor of a non-homogeneous universe" www.physicsforums.com/showthread.php?t=460495 Think of a McLaurin series expanding the metric wrt any event on any Lorentzian four-manifold. To first order it...

BRS: the bump function hat from MTW Forgot to say: Schutz's textbook includes a discussion of the Heintzmann ssspf, another of the better known ssspf solutions. The review by Lake and the papers by Visser at al. on ssspf solutions mention some other interesting examples, including a rather...

That is a very important point--- I hope I remembered to mention it in at least one of the other BRS threads on homology.

OK, hope you remind them of the importance of LTB and CPW (and maybe Ernst vacuums and related families) if they don't mention these.

BRS: "Interesting" Exact Solutions (off the Top of my Head) (continued) CPW models are noteworthy because (along with the boost-rotation symmetric vacuums, one could argue) they are the only known large family modeling physical interactions. Specifically: the nonlinear interaction of the...

BRS: "Interesting" Exact Solutions (off the Top of my Head) Happy New Year! In www.physicsforums.com/showthread.php?t=459863 George Jones asked for "interesting solutions" of the EFE. First let me say that PAllen is correct: while an exact solution modeling two mutually orbiting...

BRS: what systems create grav rad; what forms exterior field of a black hole? Re "Gravitational waves due to acceleration" https://www.physicsforums.com/showthread.php?t=459175 Pervect and Peter Donis correctly recalled reading that the Kinnersley-Walker photon rocket, an null...

BRS: Personal Cryptosystems for SA/Ms: What Would Einstein Have Said? The idea of a modest mailing list as mentioned in the previous post has now been tested at PF using encrypted PMs, and it works. In my Post #8 above, I mentioned the prevailing legal wisdom that To the surprise and...

BRS: the affine geometry of uniform expansion, summer projects, &c e Post #28 in "What do Astrophysicists do?" www.physicsforums.com/showthread.php?p=3054720#post3054720 great answer, and if harcel's post count rises above 600 with no problems visible, Marcel is a shoo-in for SA :smile...

BRS: another anti-BH crank thread, in which I barf Re "A new type of black hole?" https://www.physicsforums.com/showthread.php?t=458311 In his Post #1, yuiop appears to claim to have found a new explicit static spherically symmetric perfect fluid (ssspf) solution of the EFE which is...

BRS: In which I give up Re "Most power gravitational wave sources" www.physicsforums.com/showthread.php?t=458151 as I think most of you know, the strongest type of gravitational radiation, mass quadrupole radiation, results when the second time derivative of the quadrupole moment of the...

BRS: Timelike Congruences: Abreu and Visser 1012.4806 Under the tendicity of conflicting impulses, and in the hope that the BRS may develop into something useful and used after my departure, I add this footnote to the preceding thread: A commendable new eprint by Abreu and Visser 1012.4806...