Sebastian Schuster (Prague): Distracted by Science-Fiction: The Physics of Reverse-Engineered Metrics

Reverse-engineered metrics are ad-hoc metrics; instead of using the Einstein equation to solve for a metric given a stress-energy tensor as input, the metric is the input and the stress-energy tensor the output. Much of the attention is taken up by metrics inspired by science fiction:
Wormholes, warp drives, tractor beams. Historically, however, this was not the case, as both the Gödel universe and regular black holes are similarly reverse-engineered.
The goal of this talk will be to demonstrate how the mathematical simplicity (differentiation instead of integration) is gained through physical difficulty.
Usually, this is reduced to a question of physicality. Worse, this question is then in turn answered in an oversimplified way by invoking (point-wise) energy conditions.
I will demonstrate why energy condition cannot easily separate the physical wheat from the metric chaff, and how the question of physicality itself is much more nuanced, model-dependent, and multiform. In addition, I will make the case that reverse-engineered metrics can also serve as valuable toy models for a host of other physics questions-just as they begun their journey at the hands of Gödel.