Boyer-Lindquist space-times and beyond: Meta-material analogues

TL;DR

This paper develops methods to model complex, rotating space-times using metamaterials in laboratory settings, focusing on Boyer-Lindquist metrics and providing tools for simulating various curved geometries.

Contribution

It introduces a framework for deriving metamaterial susceptibility tensors for a wide class of space-times, emphasizing the use of the threaded formalism over ADM for tractability.

Findings

Metamaterial analogues can model Boyer-Lindquist space-times.

The threaded formalism is more effective than ADM for this purpose.

Tools are provided for simulating various curved space-times in flat laboratory settings.

Abstract

Analogue space-times (and in particular metamaterial analogue space-times) have a long varied and complex history. Much of the previous related work has focused on spherically symmetric models; however, axial symmetry is much more relevant for mimicking rotating systems. It is well known that physically reasonable stationary axisymmetric space-times can, under very mild technical conditions, be put into Boyer--Lindquist form. Unfortunately, a metric presented in Boyer--Lindquist form is not well adapted to the "quasi-Cartesian" analysis that we developed in our previous articles on "bespoke analogue space-times". Herein, we shall first focus specifically on various space-time metrics presented in Boyer--Lindquist form, and subsequently determine a suitable set of equivalent metamaterial susceptibility tensors in a laboratory setting. We shall then turn to analyzing generic space-times, not even necessarily stationary, again determining a suitable set of equivalent metamaterial susceptibility tensors. Perhaps surprisingly, we find that the well-known ADM formalism proves to be not particularly useful, and that instead the dual "threaded" (Kaluza--Klein--inspired) formalism provides much more tractable results. While the background laboratory metric is (for mathematical simplicity and physical plausibility) always taken to be Riemann flat, we {will} allow for arbitrary curvilinear coordinate systems on the flat background space-time. Finally, for completeness, we shall reconsider spherically symmetric space-times, but now in general spherical polar coordinates rather than quasi-Cartesian coordinates. In summary, this article provides a set of general-purpose calculational tools that can readily be adapted for mimicking various interesting (curved) space-times by using nontrivial susceptibility tensors in general (background-flat) laboratory settings.