Comment on "Failure of standard conservation laws at a classical change of signature"

TL;DR

This paper clarifies that matter conservation and junction conditions hold at a change of signature when the field equations are satisfied, correcting misconceptions about their failure due to singularities.

Contribution

It demonstrates that conservation laws and junction conditions remain valid at signature change if the field equations are properly satisfied, addressing previous misconceptions.

Findings

Conservation laws hold at signature change when field equations are satisfied.

Misinterpretations arose from singularities in the equations at signature change.

Proper understanding of the equations resolves previous claims of failure.

Abstract

Hellaby & Dray (gr-qc/9404001) have recently claimed that matter conservation fails under a change of signature, compounding earlier claims that the standard junction conditions for signature change are unnecessary. In fact, if the field equations are satisfied, then the junction conditions and the conservation equations are satisfied. The failure is rather that the authors did not make sense of the field equations and conservation equations, which are singular at a change of signature.