All changes, even the most longed for, have their melancholy, for what we leave behind us is a part of ourselves. We must die to one life before we can enter another.
Madness string 2477
Theorists also consider the possibility that dark matter also includes gravity leaking into our universe from neighbouring universes. If our universe is on a membrane floating within a higher dimensional space, dark matter may be explained by ordinary stars and galaxies on nearby membrane sheets.