Just a little more on the balls in the urn thought experiment. As the balls numbered 1,2,3 etc are put into the urn in successive intervals (01/2],(1/2,3/4] etc The urn has an infinite number of balls at t =1. But no ball is put in at t= 1. So the number of balls must have already become infinite at some instant before t=1. But at no name able instant can this be the case.
A variant on this. An infinite set is not the successive union of sets of its individual members. Now the set of points traversed by a particle in motion , though traversed ' one at a time' Is infinite. So, is it that the motion is better described as traversing an interval dx,how so ever Small, in a time interval dt,,rather than as being at a point x at an instant t? -Apoorv