Technically, we reject Newtonian mechanics as they relate to time, length and mass at speeds < the speed of light even though differences are infinitesimal.
Yet, a two-dimensional theory does not directly address the question. Pinning 'no beginning and no ending' on "Spatial curvature" does not solve the three dimensionality dilemma of the infinite universe
I understand that but its use has only been documented in the late 18th century (see above). Being used earlier in its complete format lacks verifiable evidence.
Without using ' opposite charges of matter' explanation as a foundation for defining anti-matter, I wonder if anyone can present a more direct definition and examples.