Floating in a boundless inter-dimensional phase space, Strange sees an “S” of earths collapsing into red cosmic dust, headed toward a galactic spire of doom.

This is related to the mathematical construct of a 'caustic', a formal singularity or concentration in phase space.

Their true venue is a ginormous abstract realm of possibilities—in the jargon, a “phase space” commensurate with their almost unimaginably rich repertoire of behaviors.