Is dark matter a broken mirror universe of our own?Dark UniverseYou know dark matter, the mysterious stuff that most physicists now believe makes up the bulk of the universe — even though it remains completely undetectable, except for its gravitational effects on regular matter?There's no shortage of far-out theories about the hypothetical material: that it's hiding inside an extra dimension, that it originated in a second Bing Bang, that it's information itself, or even that it doesn't exist at...