Cosmic cable

TL;DR

This paper analyzes the relativistic mechanics of extended cables in static, spherically symmetric spacetimes, exploring their potential for energy extraction and thermodynamic tests near black holes and cosmological horizons.

Contribution

It extends previous work on stationary cables to include rigid motion, demonstrating energy harvesting capabilities and conservation of Killing energy in such systems.

Findings

Energy harvested can reach the cable's rest mass value.

Total Killing energy of the system remains conserved.

Rigid motion allows for energy extraction via turbines.

Abstract

I investigate the relativistic mechanics of an extended "cable" in an arbitrary static, spherically symmetric spacetime. Such hypothetical bodies have been proposed as tests of energy and thermodynamics: by lowering objects toward a black hole, scooping up Hawking radiation, or mining energy from the expansion of the universe. I review existing work on stationary cables, which demonstrates an interesting "redshift" of tension, and extend to a case of rigid motion. By using a partly restrained cable to turn a turbine, the energy harvested is up to the equivalent of the cable's rest mass, concurring with the quasistatic case. Still, the total Killing energy of the system is conserved.