The forces and Penrose process in Friedman spacetime

Abstract

In this paper, we compare the force expressions in both comoving synchronous and Ellis coordinate systems in Friedman-Robertson-Walker spacetime in order to understand how the coordinate transformation affects the inertial forces. We also studied the negative energy problem in Ellis system. The Penrose process is possible outside the apparent horizon due to the fact that the line element has off-diagonal term. However, only the movement towards infinity is possible; we offer the way how one can ascertain that this effect took place outside the apparent horizon.

Keywords

• FRW metric
• inertial forces
• Ellis system
• apparent horizon
• geodesics
• negative energy