Tractor beams, pressor beams, and stressor beams in general relativity

TL;DR

This paper explores the theoretical possibility of gravitational tractor, pressor, and stressor beams in general relativity inspired by science fiction, analyzing their metrics and energy condition violations.

Contribution

It introduces a versatile warp drive-based ansatz to construct various gravitational beam metrics and discusses their physical plausibility and implications.

Findings

All proposed beams violate energy conditions.

The ansatz can produce both attractive and repulsive gravitational effects.

Implications for advanced civilizations' ability to manipulate gravity.

Abstract

The metrics of general relativity generally fall into two categories: Those which are solutions of the Einstein equations for a given source energy-momentum tensor, and the "reverse engineered" metrics -- metrics bespoke for a certain purpose. Their energy-momentum tensors are then calculated by inserting these into the Einstein equations. This latter approach has found frequent use when confronted with creative input from fiction, wormholes and warp drives being the most famous examples. In this paper, we shall again take inspiration from fiction, and see what general relativity can tell us about the possibility of a gravitationally induced tractor beam. We will base our construction on warp drives and show how versatile this ansatz alone proves to be. Not only can we easily find tractor beams (attracting objects); repulsor/pressor beams are just as attainable, and a generalization to "stressor" beams is seen to present itself quite naturally. We show that all of these metrics would violate various energy conditions. This will provide an opportunity to ruminate on the meaning of energy conditions as such, and what we can learn about whether an arbitrarily advanced civilization might have access to such beams.