“The question as to whether a solution which one has found by mathematical reasoning really occurs in nature … is a quite difficult and ambiguous one,” he explained in 1949, concerning the behavior of shock waves produced by the collision of gas clouds in interstellar space. “We have to be guided almost entirely by physical intuition in searching for it … and it is difficult to say about any solution which has been derived, with any degree of assurance, that it is the one which must exist.”
