 Many of the students seemed to be struggling to move from questions that are difficult, if not impossible, to answer because of our practical limitations (e.g., not being certain that a particular grain of sand has not already been counted) to questions that in principle are unanswerable. Finally, with a mischievous grin on his face, one of the students asked, “Will time end?” The problem, he explained, is that if time did end, no one would be able later to confirm that this was so.