Isaac Asimov, a student at Columbia at this time, remembers Urey lamenting, perhaps too strongly, how pained he was that he could do nothing to help the war effort. Asimov pointed out innocently that perhaps the enriched uranium kept at Columbia may have had something to do with the war effort. Urey reddened and changed the subject. Urey had worried about the German atomic bomb while working on uranium separation at Columbia during the war, and now referred to "the most dangerous situation that humanity has ever faced in all history".