the “black hole laser" mechanism[@jacobson1999]. The behavior of this lasing mechanism, and its potential role in laboratory realizations of Hawking radiation has been extensively investigated[@Coutant:2009cu; @parentani2010]. It could enhance the signal of Hawking radiation but, even if the initial trigger for the lasing were spontaneous emission of Hawking radiation, the amplified signal, once it had grown significantly, would be a coherent state of phonons which would be difficult to distinguish from a classical wave. Moreover, a lasing mode could be excited by a classical seed.

In the work reported here, we have investigated the dynamics of the condensate of the experiment of Ref. [@nphys3104], using primarily the one dimensional, time-dependent Gross-Pitaevskii (GP) equation. (We used the three-dimensional GP equation only to check that the qualitative features of the dynamics are the same as for the one-dimensional case.) The GP equation is a nonlinear Schrodinger equation, approximating the behavior of the expectation value of the many body field operator, which captures the classical, hydrodynamic aspects of the BEC, as well as interference phenomena. Effects of quantum fluctuations can be treated approximately by adding to the GP wavefunction an initial distribution of random fluctuations with the Gaussian statistics of the zero point 