Validity of general relativity in the strong-field regime

Determine whether Einstein’s general relativity accurately describes gravity in the strong-field regime at all scales below the Planck scale, or whether strong-field gravitational phenomena require a modified theory of gravity.

Background

The paper surveys theoretical foundations and observational breakthroughs in gravitational-wave physics, emphasizing how detections from compact-object mergers probe extreme gravitational environments. After outlining current and future detector capabilities, the author highlights that these observations enable unprecedented tests of gravity under strong-field conditions near black holes and neutron stars.

Against this backdrop, the author explicitly identifies a central unresolved question in fundamental physics: whether general relativity remains universally valid in the strong-field regime (potentially up to but excluding the Planck scale), or if modifications to gravity are needed to explain strong-field behavior. Resolving this question would clarify the theoretical framework governing the most extreme gravitational phenomena accessible through gravitational-wave astronomy.

References

However, one central question remains open: Will it be possible to take a decisive step in fundamental physics and fully understand gravity in the strong-field regime? In other words, is general relativity valid at all scales except possibly at the Planck scale, or is the strong-field regime governed by a modified theory of gravity?

— When spacetime vibrates: An introduction to gravitational waves  (2512.22679 - Lemos, 27 Dec 2025) in Section X. THE PRESENT AND THE FUTURE

Several questions, however, remain open. One is to test the robustness of AWIG by enlarging the theory space beyond the minimal Palatini f(R) sector to include derivative-dependent exponents. Such terms are motivated both by the dimensional-reduction analysis in Ref., which suggests that the exponent n may contain differential structure, and by the possibility that a genuinely differential relation could soften some of the known pathologies of Palatini models. Their implications for strong-field phenomenology and ultraviolet closure, however, require a separate analysis and are left for future work.

— Ultraviolet Closure in Asymptotically Weyl-Invariant Gravity  (2609.01047 - Coumbe, 1 Sep 2026) in Section 5, Discussion and conclusions