Science fiction has a field day inventing plots with alternate universes.  The terribly written show Sliders did this in the 1990's (I couldn't watch beyond 3 episodes, the writing was so weak) and the better scribed but not superb Fringe explores this now.  Sliders embraced the concept of an infinite number of alternate universes.   Fringe practices the "keep it simple, stupid" mantra, pulling any science it can from dubious Wikipedia articles, and limits the number of universes to two. 

I first remember encountering the alternate universe concept in 1987 when I read the book Timescape.  A scientist from 1962 receives interference signals from 1998, warning the past of impending ecological disaster.  The scientist from 1962 acts on these findings and changes the future.  His 1998 will wind up very differently from the 1998 sending back the messages.  That the messages were sent from somewhere means that there are at least two universes; and if there can be two universes based on group choices, there can be an infinite number based on an infinite number of choices made by the billions of people occupying this planet. 

Alternative universes offer an explanation for the infamous Grandfather Paradox.  If I am able to journey back in time and murder by grand daddy, how then can I be born?  Well, I can't -- not on that timeline.  By killing my grandfather, I've created an alternate universe in which my father could never be born to ever marry my mother.    The original universe, the one in which I was born, continues to exist in parallel with the alternate one(s). 

New age practitioners have embraced alternate universes.  Quantum jumping suggests you can converse with your alternate selves through meditation to borrow abilities the other you's have cultivated.  If, for instance, you get a vision of an alternate you being thinner but having the hair combed differently, you're to comb your hair in that same way to more closely mirror this alternate self and, hence, borrow the thinner frame, too.    The Heisenberg uncertainty principle says that you can only state a probability that an electron is in a certain location.  You cannot both measure precision and momentum accurately.   You could say that each possible location of the electron represent a different alternate universe. 

None of this can be proven in peer reviewed scientific journals though.  The way our universe works is that once we make a choice, to attend Harvard instead of Jackass State University as an example, all the subsequent actions that would've resulted from the other choice cease to exist for us.  Flip a coin and it lands heads, the tail possibility no longer exists on that flip.  When we look back on our lives, we see only one distinctive path, the path we took.  The other pathways disintegrate when we choose not to go down them. 

Fringe throws all science to the winds in its alternate universe pedagogy.  In their alternate universe, U.S. state names are different and yet all the main characters work for the same department in both universes and some even live at the same addresses.  The identical movies will have been produced in both universes but with different lead actors.  Traveling physically from one universe to the other is easy.   Deprive your senses in a deprivation chamber and inject yourself with a few drugs and off you go. 

Carlo Rovelli first proposed in his relational interpretation of quantum mechanics that an electron can appear to be in two places at once when observing patterns in Thomas Young's double slit experiment.  I, too, can be in two places at the same time - or millions - if you consider all the me's in all the alternate universes as just expressed possibilities.  One me might be living in France, another in Texas, another in Thailand.  If you were to graph these possibilities, I believe you'd see something similar to an electron probability distribution function, with the highest probabilities indicating the choices most me's would've made.

Science fiction television shows and movies ignore most science and logic.  Let's take it that I exist in N different alternate universes, N representing some humungous number approaching infinity.   In every single one of those universes, I would necessarily have to have the same parents, and every event preceding my birth would have to be exactly the same in all those N universes in order to lead up to my conception.    Understand that the odds of any of us being born are extremely small.  If my parents had decided to conceive me minutes earlier or later, a different sperm would have reached the egg.  Let that sink in.  If you could travel back to January 1, 1960, and cause a mere 2-second delay that would affect the actions of everyone on the planet by 2 seconds, every single person conceived after this date could have different genetic codes compared to the people conceived without that 2-second delay.  Mr. and Mrs. Ralph Jones who bore their child Ralph, Jr on October 5, 1960 could still have a Ralph, Jr, but he'd be a genetically different Ralph, Jr.  And so a different Ralph, Jr would procreate with a different spouse and create different combinations of children.  Only in some of the cases, who knows how many, the original quickest sperm will still reach the same egg but 2 seconds later, and the same person with the same genetic code will be born..  Expand the delay to 5 seconds, 10 seconds, or a still paltry 30 seconds, the odds of your conception go increasingly downhill. 

Thus, every alternate universe in which I exist can't really be all that different from the one I'm currently living in.  My older sister and aunts and uncles would be the same.  My family would've lived in the same apartment we resided in until I was 6 months old, and it's likely we would've moved into the same house afterwards.  My father would still have been a surgeon.  Perhaps, a year-and-a-half later, I would've had a different looking younger brother or maybe a sister this time.  (Remember that I exist in all my younger brother's universes, but he only exists in some of mine).  A different brother, even if he had the same name as my current brother, or a sister affects our family dynamics in a different way and greater deviations from that universe to this one would have resulted.  As time passed, the universes could begin to look more and more different.

But not in the exaggerated ways depicted in bogus sci-fi flicks.  For most of us, in rather superficial ways.   If you graduated college in this universe and married your college sweetheart or someone you met shortly out of college, you would probably have still married a college sweetheart in a different universe.  It might just be a different college and a different sweetheart.  If you opted for a safe profession like accountancy in this universe, I'll bet you're doing the same job, but maybe at a different company, in an alternate universe.  To think you would've wound up a president/prime minister or CEO of a multibillion dollar company, though possible, doesn't get much credibility if you've always been opting for the middle of the road in this universe.

Where it gets more interesting is for those people who've lived their lives on the edge.  These people took greater risks.  Deciding whether to go to Harvard or Yale before you go on to laws school is not, in the scheme of things, a major universe-altering event.   Deciding whether to go to college at all or to drop out of college is.    Whether you crunch numbers for Proctor & Gamble or you do it for Wal Mart isn't going to spin your life in an entirely new direction; but whether you decide to work for a multinational or a startup is.  Marrying the first sweetheart you meet in college or pushing for a marriage on Jdate or Match.com isn't the risk that holding out for a soulmate is. You may never meet that soulmate and, thus, never marry, a greater risk for sure.   Being a real gambler, the kind to gamble on crap games and roulette wheels, is a great risk. Odds are, if you're an addict, that you're broke in all the universes.   More level-headed gamblers, such as investors who feel they can tilt the playing field more to their favor because they're armed with insights not gleaned by the general masses, are still significant risk takers. In universes where some of their leaps of faith played out, they'll be immensely rich; in universes where an assumption failed, they won't be.

Ditto for many famous celebrities, also big risk takers.   For many a star, their career was launched into the stratosphere off one pivotal role.  For Dustin Hoffman, it was his 1967 lead in The Graduate. Clint Eastwood only got wide acclaim after appearing in Sergio Leone's spaghetti westerns in the mid-1960's.  Harrison Ford, from Star Wars. TV stars are the most notorious for having careers built on single roles.  Would Ted Danson (Cheers), Jason Alexander (Seinfeld), or Jennifer Aniston (Friends) have ever had their illustrious careers if someone else had been cast in their fame-breaking roles in an alternate universe?  Luck plays a significant role here, and you can't count on luck playing out the same way in most alternate universes.   So if you're living on the top of the world right now and much of your success can be attributed to a lucky break you couldn't re-engineer even with a bribe or by putting out strategically, rest easy that the current you is living better than the alternate you's in 99% of all the other universes in which you exist. 

A good many of us acquire destructive tendencies, habits, and behaviors during our youth which we take into adulthood. We quite literally sabotage our own chances at success and happiness over and over again.  I know a man of nearly 40. He grew up with no father figure and this affects his relationships with women today and not for the better.  He'll always find a reason to escape from any relationship he's in, the reasons steadily becoming more and more ridiculous over time.   When I met him 4 years ago, the excuses started with "She's got a slight acne problem" and it's since progressed to "Her legs are too skinny."   In an alternate universe, his father may have been a more nurturing figure.  That simple change of detail in his past could have paved the way for a more prosperous and productive adulthood.  Now it is out of this man's control in every universe what kind of father he had, but it was always fully in his power to assess the roadblocks brought on by his upbringing and do what he could to move past them, and in a few alternate universes, he may have done just that.

Let's say that you are born with a congenital heart defect that's certain to kill you before age 50.  The you's in every alternate universe, born to the same parents, would share this same heart anomaly.  Perhaps in a few select alternate universes, a miraculous medical advance occurs pertaining precisely to your heart problem. In most, you're destined to die before  50.  How the you in that universe is raised to deal with this early visit with the reaper determines what kind of person you'll end up in that universe.   Since your reaction to your defect will be predominantly shaped by the way your parents accept your limited life span, and their reaction in your formative years is outside your control, you're probably going to see a very similar you in the majority of universes.

A person born with a golden spoon in his mouth would've been born with a similarly expensive spoon in every universe.  But money and access to the greater opportunities it brings at a younger age, while contributing largely to a greater scale of happiness, isn't the sole determinant.  Still, I will say from observation that getting served a combination platter of money, happiness, and contentedness in any life isn't easy to come by.  It's just too damned easy for things to go pear shaped along the way.  If you're one of the few experiencing bliss now, in this universe, you must be doing something extraordinarily right, and for once, it might really ring true that there's no place quite like home.