This will be judged true if there are at least 100 papers authored by a total of at least 50 different scientists, appearing in peer-reviewed science journals which cite published articles describing the principle of event-symmetric space-time, or physical models explicitly incorporating the principle.
The peer-reviewed journals may be published on paper, electronic or other media but must be serious science journals with articles reviewed by scientists. They must have actually appeared in final form in the journal before the claim's closing date. Citations in a paper which is authored or co-authored by an author of the article cited will not count towards the count of citations, but can count towards the count of scientists.
The articles cited may include any published work on event-symmetric space-time, even e-prints and web-pages which need not have been reviewed. Citations of unpublished articles such as private communications will not count.
A more detailed exposition of the theory can be found at http://ourworld.compuserve.com/homepages/Phil_Gibbs/esst.htm.
I plan to keep a list of any citations which count towards this claim at http://ourworld.compuserve.com/homepages/Phil_Gibbs/cite.htm.