In Bacillus subtilis colonies, motile bacteria move collectively, spontaneously forming dynamic
clusters. These bacterial clusters share similarities with other systems exhibiting polarized collective
motion, such as bird flocks or fish schools. Here we study experimentally how velocity and orientation
fluctuations within clusters are spatially correlated. For a range of cell density and cluster size, the
correlation length is shown to be 30% of the spatial size of clusters, and the correlation functions collapse
onto a master curve after rescaling the separation with correlation length. Our results demonstrate that
correlations of velocity and orientation fluctuations are scale invariant in dynamic bacterial clusters.