Analogue transformation acoustics and the compression of spacetime
  A recently developed technique known as analogue transformation acoustics has allowed the extension of the transformational paradigm to general spacetime transformations under which the acoustic equations are not form invariant. In this paper, we review the fundamentals of analogue transformation acoustics and show how this technique can be applied to build a device that increases the density of events within a given spacetime region by simultaneously compressing space and time. 
C. Garc\'ia-Meca, S. Carloni, C. Barcel\'o, G. Jannes, J.   S\'anchez-Dehesa, A. Mart\'inez
gr-qc cond-mat.mes-hall cond-mat.mtrl-sci