- qc / 0 50 61 17 v 1 2 3 Ju n 20 05 Building a case for a Planck - scale - deformed boost action : the Planck - scale particle - localization limit

" Doubly-special relativity " (DSR), the idea of a Planck-scale Minkowski limit that is still a relativistic theory, but with both the Planck scale and the speed-of-light scale as nontrivial relativistic invariants, was proposed (gr-qc/0012051) as a physics intuition for several scenarios which may arise in the study of the quantum-gravity problem, but most DSR studies focused exclusively on the search of formalisms for the description of a specific example of such a Minkowski limit. A novel contribution to the DSR physics intuition came from a recent paper by Smolin (hep-th/0501091) suggesting that the emergence of the Planck scale as a second nontrivial relativistic invariant might be inevitable in quantum gravity, relying only on some rather robust expectations concerning the semiclassical approximation of quantum gravity. I here attempt to strengthen Smolin's argument by observing that an analysis of some independently-proposed Planck-scale particle-localization limits, such as the " Generalized Uncertainty Principle " often attributed to string theory in the literature, also suggests that the emergence of a DSR Minkowski limit might be inevitable. I discuss a possible link between this observation and recent results on logarithmic corrections to the entropy-area black-hole formula, and I observe that both the analysis here reported and Smolin's analysis appear to suggest that the examples of DSR Minkowski limits for which a formalism has been sought in the literature might not be sufficiently general. I also stress that, as we now contemplate the hypothesis of a DSR Minkowski limit, there is an additional challenge for those in the quantum-gravity community attributing to the Planck length the role of " fundamental length scale ". One might say that special relativity went into retirement at a very young age, since the advent of general relativity, in 1916, took away from special relativity the status of " fundamental " ingredient of the laws of Nature. But actually special relativity, now 100 years old, continues to work hard for physicists. In quite a few contexts involving gravitational phenomena one gets away describing the spacetime metric g µν in terms of a Minkowski background metric, η µν , and a " gravity field " Lorentz tensor h µν , related to g and η by the relation h µν = g µν − η µν. And special relativity still reigns supreme in the vast class of phenomena studied in particle physics, where one can safely 1 This essay received an honorable …