text: A computer simulation of a typical bathroom found that none of the above theories pan out in their analysis, but instead found that the spray from the shower-head drives a horizontal vortex. This vortex has a low-pressure zone in the centre, which sucks the curtain.
  David Schmidt of the University of Massachusetts was awarded the 2001 Ig Nobel Prize in Physics for his partial solution to the question of why shower curtains billow inwards. He used a computational fluid dynamics code to achieve the results.  Professor Schmidt is adamant that this was done "for fun" in his own free time without the use of grants.