It depends if relativistic behaviour is emergent or fundamental. The whole point of the &quot;spacetime is quantised&quot; argument isn&#x27;t just to suggest that spacetime comes in little lumps, but to investigate the possibility that the properties of spacetime - including curvature, relativistic effects, and all the weirdness in quantum theory - emerge from a common fundamental description.<p>Planck-scale invariance is a red herring - or rather, it&#x27;s a naive assumption that may not be accurate. There isn&#x27;t really much useful theory or experimental evidence in Planck-scale physics.<p>For an overview, see<p><a href="http:&#x2F;&#x2F;newt.phys.unsw.edu.au&#x2F;einsteinlight&#x2F;jw&#x2F;module6_Planck.htm" rel="nofollow">http:&#x2F;&#x2F;newt.phys.unsw.edu.au&#x2F;einsteinlight&#x2F;jw&#x2F;module6_Planck...</a>