What is this strange universe, and what became of the thirty years that seem to me less than a month?"

Somehow I knew the answer, must have reasoned it out subconsciously as he spoke. "Science has moved while you were gone, Jay. We know now that the ether eddy is the manifestation Of a fourth dimensional tangency between two spatial hyperspheres.* You remember your high school Einstein, don't you?"

[* The figure in four-dimensional geometry that is analogous to a sphere in three-dimensional i.e., the figure described by a sphere rotated through the fourth dimension, as a circle is rotated through the third dimension to describe a sphere.]

"Of course. I get it. Einstein said space, our space, is unbounded but finite, the three-dimensional surface of a hypersphere within which, and without, nothing exists that is in any way related to anything in our space. What's happened is that we've—"