Speaker
Description
As proven by Simon, Beig, and others from the 1960s on, Einstein spacetimes are uniquely decomposable into a set of multipole moments. The Geroch-Hansen or Thorne moments are often used to categorise radiation patterns, tidal deformations, geodesics, and other phenomena associated with compact objects, and these theorems ensure such descriptions are complete in some sense. What if we drop the "Einstein" qualifier? In fact, I will argue via counterexamples that this breaks the uniqueness properties and thus it is ambiguous to describe astrophysical observables in terms of moments unless the theory is fixed a priori. This has implications for null tests of general relativity. More generally, I will discuss why these degeneracies could be important to recognise in the context of several well-studied results, like the "I-Love-Q" relations featuring a quadrupole moment (Q).
| Research Area | Mathematical and Numerical Relativity |
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