  The last decade of research on $\kappa$-Minkowski noncommutative spacetime
has been strongly characterized by a controversy concerning the speed of
propagation of massless particles. Most arguments suggested that this speed
should depend on the momentum of the particle strongly enough to be of interest
for some ongoing experimental studies. But the only explicit derivations of
worldlines in $\kappa$-Minkowski predicted no momentum dependence for the speed
of massless particles. We return to this controversy equipped with the recent
understanding (arXiv:1006.2126, arXiv:1007.0718, arXiv:1008.2962,
arXiv:1101.0931) that in some quantum spacetimes coincidences of events
assessed by an observer who is distant from the events can be artifactual, and
particularly Smolin's thesis (arXiv:1007.0718) that $\kappa$-Minkowski should
be an example of such a spacetime. We therefore set up our investigation in
such a way that we never rely on the assessment of coincidences of events by
distant observers. This allows us to verify explicitly that in
$\kappa$-Minkowski simultaneously-emitted massless particles of different
momentum are detected at different times, and establish a linear dependence of
the detection times on momentum.

High Energy Physics - Theory