Ken Levine, in the third developer video for Bioshock Infinite, discusses the Tears, which are “Windows into Other Worlds.”
Elizabeth’s magic isn’t so much mystical as it is focusing on the physics research of the turn of the century, with such concepts as Heisenberg and Einstein being brought into fruition, and the concept of the multiverse, in which layers of probability can be explored by Elizabeth, tearing into the fabric of reality and bringing them into our universe.
This is, presumably, where the “Infinite” in the title comes from.
Check out the developer diary in the video below, and let us know if this makes you even MORE excited for the game.