Gödeluniversumet

Gödeluniversumet, commonly known as the Gödel universe, is a solution to Einstein's field equations discovered by Kurt Gödel in 1949. It describes a spatially homogeneous, rotating universe filled with a pressureless perfect fluid (dust) and a nonzero cosmological constant. The model is stationary and does not exhibit cosmic expansion as in the standard cosmology; instead, it features global rotation of spacetime.

A notable feature of the Gödel universe is the presence of closed timelike curves, meaning that there are worldlines that return to their starting events in the past. These curves arise from the spacetime geometry at sufficiently large distances from the rotation axis, raising implications for causality in general relativity. The solution therefore serves as a theoretical counterexample to the idea that general relativity alone enforces causality universally.

Historically, Gödel introduced the model to demonstrate that Einstein's equations do not by themselves prevent time travel in principle, and it has since become central to discussions of chronology protection and the limits of relativity. In practice, the Gödel universe is considered physically unattractive: it requires a global rotation that is not supported by observations, and it does not describe our expanding, nearly isotropic universe.

See also: closed timelike curve, general relativity, cosmological constant, chronology protection conjecture.