Unusual causal structure in general relativity is evidence against its correctness

In our previous blog posts we wrote that (linearized theory) gravitational waves seem to allow one to travel back in time. That would bring all the time travel paradoxes, and be strong evidence against the correctness of general relativity as a physical theory.

https://journals.aps.org/rmp/abstract/10.1103/RevModPhys.37.215

It turns out that Roger Penrose observed the problematic causal structure back in 1965.

"The following remarkable property is then obtained. No spacelike hypersurface exists in the space-time which is adequate for the global specification of Cauchy data."

Roger Penrose writes in the abstract of the paper that one cannot specify the initial values (Cauchy data) on a spacelike hypersurface.

https://arxiv.org/abs/hep-th/0211195

Veronika E. Hubeny and Mukund Rangamani (2002) state that "even the causal structure of pp-waves is different from that of flat spacetime."

https://en.wikipedia.org/wiki/Pp-wave_spacetime

A serious flaw in a physical theory is considered an exciting opportunity for science fiction

It is conspicuous that authors seem to consider a strange causal structure as "remarkable" or "interesting", rather than start to question the validity of the theory. If one would introduce a theory of electromagnetism which has a unusual causal structure, people would immediately suspect that the theory is flawed.

The Gödel metric, which has circular causal paths, is another instance where one should start to think if general relativity is broken.

In the Kerr metric there are circular causal paths, like in the Gödel metric.

Wormholes and the Alcubierre drive are other examples where circular causal paths appear.

People seem to hope that a time machine or a warp drive exists, even though it would make the physical theory contradictory.