Such a step, he said, would require only two stages; first, a passage out of the three-dimensional sphere we know, and second, a passage back to the three-dimensional sphere at another point, perhaps one of infinite remoteness. That this could be accomplished without loss of life was in many cases conceivable. Any being from any part of three-dimensional space could probably survive in the fourth dimension; and its survival of the second stage would depend upon what alien part of three-dimensional space it might select for its re-entry. Denizens of some planets might be able to live on certain others—even planets belonging to other galaxies, or to similar dimensional phases of other space-time continua—though of course there must be vast numbers of mutually uninhabitable even though mathematically juxtaposed bodies or zones of space.