Note that different people have different research approaches. The two old ladies check that none of them can see herself and the problem is solved! ;-)
The other older lady makes an experiment with motion and rigorously determines that she is ... well ... unsichtbar. :-)
Seven Must-Read Stories (Week Ending July 4, 2015) - Another chance to catch the most interesting, and important, articles from the previous week on *MIT Technology Review*.
9 hours ago