Somewhere in the muddle of the dreaded holiday season, I managed to fit in a Doctor Who marathon as an antidote to a suddenly colicky baby. Thank you, BBC America! Between the Doctor and Torchwood, I need never watch bad American sitcoms again. That is, if they’d stop giving us neverending episodes of “You Are What You Eat” and “Ramsey’s Kitchen Nightmares.”

Since the real BBC seasons are far ahead of what is shown on BBC America, the season finale of Doctor Who on this rebellious side of the pond was the one where the Cybermen cross universes and surviving Daleks emerge from the Void to battle each other — lots of fun when sci-fi’s biggest evildoers run around (or zoom around) chanting “Delete” and “Exterminate” at one another. Of course, the good Doctor sends them both back to the Void, or hell. And he repeatedly tells people traveling to different universes themselves of the damage they’re doing to their respective realities. “You can’t cross universes,” he says.

But what if you could? You know all those glossy travel mags, the ones with a smashing beach or mountain climbing photo on the front that advertise “10 Best Places to Escape” or “5 Undiscovered Islands” or “The World’s Best Climbing Challenges?” What if instead they read “5 Undiscovered Realities,” “Your Life: 10 Exciting Alternatives,” or “Our Picks: The Best Untouched Universes.”

Even lifestyle magazines could chip in. Women’s: “What if you had married your high school sweetheart? One inter-universal traveler’s story.” “Career or Kids? Investigate your options in other realities!” And men’s: “What if you hadn’t gotten her pregnant?” “Meet the stud you really are!” “Stunted careers: find out where you went wrong.”

The Doctor Who episode, while fanciful, is based on a very real theory called the Many-Worlds Interpretation of quantum mechanics, which isn’t expressed quite so simply as, “Every single choice you make births a new universe.” But close enough.

Think of the travel opportunities! Instead of teaching English in Korea, you could teach American English in a reality where the American Revolution had never happened. Instead of being awed by increasingly empty Gothic churches leftover from a world dominated by Catholicism, you could shiver in — and then safely leave — a universe in which the Roman church and the Inquisition gained power rather than lost it. Or travel by buggy in an existence in which the steam engine was never invented. Or slip secretly across to watch what would have happened with her/him if you had made the right move at the right time.

Where would you go?