Parallel worlds are a topic of science fiction that seem to come up over and over again. Lately,
the number of shows and movies featuring branching timelines and multiverses have been multiplying,
and you may be low-key wondering just how much of the fiction resembles reality.
Scientists have been asking these same questions for decades because from what we’ve seen,
the future is far from certain. The idea of multiple worlds is compelling because it solves a
thorny issue that arises from quantum mechanics. Classical physics is typically thought to be
deterministic: if you know the speed and position of something like a ball flying through the air,
then you can predict where the ball is going to land.
But in the quantum world, things don’t work like that.
It is impossible to know the exact speed and position of a particle like an electron,
and so it is impossible to say for certain what it will do, only the probabilities.
The mathematical expression of all known possibilities of a particle's location
and characteristics is called its wave function. Bizarrely, in the quantum
realm particles appear to exist in multiple states simultaneously, until something causes
only one outcome to result, what’s known in science-y talk as “collapsing the wave function”.
The mechanism that causes wave functions to collapse is still debated, but one of
the most widely accepted is the Copenhagen Interpretation. It states wave functions
collapse when they are observed, measured, or interact with the classical world in some way.
It sounds bizarre but that’s a conclusion the evidence points to. It’s beyond the scope of this
video but if you want to know more about it, check out this video on the double slit experiment here.
The Copenhagen interpretation comes with its own issues, which physicist Edwin Shrodinger tried
to point out when he devised a thought experiment where a cat in a box could be both alive and dead
at the same time so long as no one looked inside. But what if we’re looking at this the wrong way,
and the wave functions don’t actually collapse? What if instead all possibilities continue
to exist and our universe simply branches off into separate worlds for each outcome?
A mind-boggling number of worlds could be constantly branching off for every
single possible outcome in this vast universe. That was the idea put forward by Hugh Everett
in 1957. It’s an intriguing thought but if the worlds are truly split,
then there’s no way to ever directly observe them, let alone open a doorway between them.
On the one hand, that’s great news if you’re worried about some some
parallel-world- hopping conqueror
suddenly showing up. On the other hand, it’s frustrating if you’re a scientist or if you have
aspirations of inter-universe conquest… or both.
Of course, the many-worlds interpretation just
creates its own set of questions, fittingly. Like, what actually causes worlds to split?
One possible mechanism is decoherence where quantum states gradually unravel as a result
of their interactions with their environment. If that’s the case, then worlds don’t have hard
splits, more like gradual separations until they reach a point when they can no longer
affect each other and are truly distinct. There are more issues with the many-worlds
interpretation, some that are more in the realm of philosophy than physics. Like,
if worlds are constantly branching off creating countless slightly different versions of you,
then what does it mean to be you? Some versions of you should be incredibly similar while a huge
number of others are profoundly different. Which one is the real one? Some physicists
might say that no single one is, but the real you is the sum total of all versions of yourself.
And other physicists might say that the whole idea of many worlds is hogwash.
The debate rages on and because there’s no proof
yet for one argument or the other, it could very well continue for a long time to come.
One thing I will confidently predict is that due to its intriguing nature and the possibilities
it opens up, the many-worlds interpretation of quantum mechanics is definitely going to be a
staple of science fiction until the end of time.
While we're still searching for branching worlds,
another universe may have bumped into ours.
Check out this video on that right here.
So, do you buy into the many worlds idea, and if so,
what do you think about all the other you's that could be running around
out there. Let us know in the comments,
be sure to subscribe, and I or some version of myself will see you next time on Seeker.