Alternate Realities and Parallel Dimensions

They may seem like movie subtitles or complicated tv show plots, but there is truth in the ideas. Would you step over the line and into a new world both similar and different to the one you know? How close are we to finding another version of you—and how many are there in existence? How would you know who's who? And are there any ethical conundrums that might be crossed with talking to yourself? If only we could ask our other selves to be sure . . .