Surprising Structures Hiding at Penrose's Future Null Infinity

Abstract

Since the late1950s, almost all discussions of Asymptotically Flat (Einstein-Maxwell) Space-Times have taken place in the context of Penrose's Null Infinity, $\mathcal{I}^{+}.$\ $\ $In addition,\ almost all calculations have used the Bondi coordinate and tetrad systems. \ We show - first, that there are other natural coordinate systems, near $\mathcal{I}^{+},$ (analogous to light-cones in flat-space) that are based on (asymptotically) shear-free null geodesic congruences (analogous to the flat-space case). \ Using these new coordinates and their associated tetrad, we \textit{define the complex dipole moment, i.e., as the mass dipole plus i times angular momentum,} from the $l=1,\ $harmonic coefficient of a component of the asymptotic$\ $Weyl tensor. Second, from this definition, from the Bianchi Identities and from the Bondi mass and linear momentum, we show that \ there exists a large number of results - identifications and dynamics - identical to those of classical mechanics and electrodynamics. They include, among many others, \textbf{P}=M\textbf{v}+..., \textbf{L}=\textbf{r}x\textbf{P}, \ spin, Newtons 2nd Law with the Rocket force term (\.{M}\textbf{v}) and radiation reaction, angular momentum conservation and others. \ All these relations take place in the rather mysterious H-Space.