Observer-independent quantum of mass

It has been observed recently by Amelino-Camelia that the hypothesis of existence of a minimal observer-independent (Planck) length scale is hard to reconcile with special relativity. As a remedy he postulated to modify special relativity by introducing an observer-independent length scale. In this Letter we set forward a proposal how one should modify the principles of special relativity, so as to assure that the value of mass scale is the same for any inertial observer. It turns out that one can achieve this by taking dispersion relations such that the speed of light goes to infinity for finite momentum (but infinite energy), proposed in the framework of the quantum kappa -Poincare symmetry. It follows that at the Planck scale the world may be nonrelativistic. (C) 2001 Elsevier Science B.V. All rights reserved.