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Open AccessArticle

Planck-Scale Soccer-Ball Problem: A Case of Mistaken Identity

1
Dipartimento di Fisica, Università di Roma “La Sapienza”, P.le A. Moro 2, 00185 Roma, Italy
2
Istituto Nazionale di Fisica Nucleare (INFN), Sez. Roma1, P.le A. Moro 2, 00185 Roma, Italy
Entropy 2017, 19(8), 400; https://doi.org/10.3390/e19080400
Received: 23 April 2017 / Revised: 10 July 2017 / Accepted: 18 July 2017 / Published: 2 August 2017
(This article belongs to the Special Issue Quantum Information and Foundations)
Over the last decade, it has been found that nonlinear laws of composition of momenta are predicted by some alternative approaches to “real” 4D quantum gravity, and by all formulations of dimensionally-reduced (3D) quantum gravity coupled to matter. The possible relevance for rather different quantum-gravity models has motivated several studies, but this interest is being tempered by concerns that a nonlinear law of addition of momenta might inevitably produce a pathological description of the total momentum of a macroscopic body. I here show that such concerns are unjustified, finding that they are rooted in failure to appreciate the differences between two roles for laws composition of momentum in physics. Previous results relied exclusively on the role of a law of momentum composition in the description of spacetime locality. However, the notion of total momentum of a multi-particle system is not a manifestation of locality, but rather reflects translational invariance. By working within an illustrative example of quantum spacetime, I show explicitly that spacetime locality is indeed reflected in a nonlinear law of composition of momenta, but translational invariance still results in an undeformed linear law of addition of momenta building up the total momentum of a multi-particle system. View Full-Text
Keywords: quantum foundations; relativity; quantum gravity quantum foundations; relativity; quantum gravity
MDPI and ACS Style

Amelino-Camelia, G. Planck-Scale Soccer-Ball Problem: A Case of Mistaken Identity. Entropy 2017, 19, 400.

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