Dimensional rift

A dimensional rift was an opening between dimensions. It was traversable, in that matter (including beings) could cross from one end to the other.

Project Infinity was developed to open such a dimensional rift on Lopra Minor. The results was contact with a Daleks with morals of a parallel universe, who immediately declared war on this universe's Daleks. (AUDIO: "Death to the Daleks!", Project Infinity)