Rewinding the Void: How One Solution of Einstein's Field Equations Describes Both the Birth of a Universe and the End of Time

TL;DR

This paper reviews the type D Kasner vacuum solution in general relativity, revealing its ability to describe both the universe's birth and black hole interiors through a reversal of time, highlighting the flexible nature of Einstein's solutions.

Contribution

It uncovers the dual role of the Kasner solution in modeling cosmological origins and black hole interiors, emphasizing the solution's time-reversal symmetry and implications for the arrow of time.

Findings

Kasner solution describes both cosmology and black hole interiors

Time reversal links the two different spacetime descriptions

Highlights the flexible and symmetrical nature of Einstein's solutions

Abstract

The type D Kasner vacuum solution of general relativity is reviewed, highlighting the little-known, intriguing property that it can describe both an anisotropic cosmology and the spacetime deep within a black hole, these two descriptions linked by a reversal of the time-ordering of the solution. The flexible nature of solutions of Einstein's equations is emphasised, and a brief discussion of the arrow of time in modern physics is presented.