According to the 'many worlds' interpretation of quantum mechanics, there may be multiple copies of us living in multiple worlds.
Ever wonder what would have happened if you'd taken up the "Hey, let's get coffee" offer from the cool classmate you once had? If you believe some of today's top physicists, such questions are more than idle what-ifs. Maybe a version of you in another world did go on that date and is now celebrating your 10th wedding anniversary.
The idea that there are multiple versions of you, existing across worlds too numerous to count, is a long way from our intuitive experience. It sure looks and feels like each of us is just one person living just one life, waking up every day in the same, one-and-only world.
But according to an increasingly popular analysis of quantum mechanics known as the "many worlds interpretation" every fundamental event that has multiple possible outcomes - whether it's a particle of light hitting Mars or a molecule in the flame bouncing off your teapot - splits the world into alternate realities.
Multiple splits, multiple worlds
Even to seasoned scientists, it's odd to think that the universe splits apart depending on whether a molecule bounces this way or that way. It's odder still to realise that a similar splitting could occur for every interaction taking place in the quantum world.
Things get downright bizarre when you realise that all those subatomic splits would also apply to bigger things, including ourselves. Maybe there's a world in which a version of you split off and bought a winning lottery ticket. Or maybe in another, you tripped at the top of a cliff and fell to your death - oops.
"It's absolutely possible that there are multiple worlds where you made different decisions. We're just obeying the laws of Physics", says Sean Carroll, a theoretical physicist at the California Institute of Technology and the author of a new book on many worlds titled "Something Deeply Hidden". Just how many versions of you might there be? "We don't know whether the number of worlds is finite or infinite but it's certainly a very large number", Caroll says. "There's no way it's, like, five".
Caroll is aware that the many worlds interpretation sounds like something plucked from a science fiction movie. (It doesn't help that he was an adviser on "Avengers : Endgame") And like a Hollywood blockbuster, the many worlds interpretation attracts both passionate fans and scathing critics.
Renowned theorist Roger Penrose of Oxford University dismisses the idea as "reductio ad absurdum" : physics reduced to absurdity. On the other hand, Penrose's former collaborator, the late Stephen Hawking, described the many worlds interpretation as "self-evidently true".
Carrol himself is comfortable with the idea that he's but one of many Sean Carrolls running around in alternate versions of reality. "The concept of a single person extending from birth to death was always just a useful approximation", he writes in his new book and to him the many worlds interpretation merely extends that idea : "The world duplicates and everything within the world goes along with it".
How did we get here?
The mind-bending saga of the many worlds interpretation began in 1926 when Austrian physicist Erwin Schrodinger mathematically demonstrated that the subatomic world is fundamentally blurry.
.........to be continued.
Tailpiece.
Got up at 6, the chores and was ready by 10. Earlier, washing machinex was carried out on the soiled clothes post-trip.
It's dad's 9th remembrance day and Lekha and I had offered 'bali tharpanam' at our courtyard. The crows took a while to peck at it.
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