Quantum mechanics is littered with different interpretations, but at the core of the entire school of thought is the question of whether there are multiple universes of not. At the core of this idea is the thought, explicated by quantum mechanics, that everything we observe is simply the collapse of all probable scenarios into one specific outcome. Reality, viewed from that perspective, has a very cluttered cutting room floor. But are the things removed from the reel scraps or alternative narratives? There’s the big question.
To answer that question, we need to dive a bit into the mechanisms of the thing. Quantum mechanics says that all particles in the universe can be represented by what are called “wave functions.” A single wave function basically illustrates all the information about a specific system (i.e. a particle), detailing everything from position to velocity. The wave function itself also outlines all the probable outcomes of that system as well.
In other words, the wave function says what a particle is, and — more importantly — what it might being doing any any given time. It represents all possible futures of that particle.
But, as any human being knows, there’s only one future a particle actually has — the future that occurs. This is also the future that we are able to measure and observe. So measuring a particle basically collapses the wave function into one single reality. This is known as wave function collapse — or quantum collapse. At least, that’s the way it goes according to one interpretation, namely the Copenhagen interpretation first pitched by famed physicists Niels Bohr and Werner Heisenberg. Zoom out on the math and the science and you get the philosophy: We are our ability to measure and observe what happens in this world.
But there’s another interpretation that doesn’t buy into this. It’s the Many World interpretation. In the 1950s, Hugh Everett proposed that wave functions actually don’t collapse. Instead, all the probable outcomes for every particle actually exist superimposed on one-another, meaning they all exist and all occur at the same time. If you don’t already understand what I’m getting at, allow me to spell it out for you: Everett’s theory basically says that the multiple possible futures for a single particle actually exist all at once. When you extrapolate that to include every particle ever in the universe, then that essentially says there is an infinite number of universes that exist in parallel.
Our observations limit us to living and breathing in just one — but that doesn’t mean the others aren’t happening. The wave function doesn’t collapse. The multiverse is real. Unfortunately, this theory can never be proven. There is no way to actually test the Many Worlds interpretation. As a part of quantum physics, it’s more philosophy than science. There’s no real place for it in the actual research world — much less the practical day-to-day world most people have enough trouble wrapping their heads around.
But there might be one way to test if quantum collapse is false. Max Tegmark of MIT discusses one kind of experiment pitched in the 1980s that proposed how you might prove a multiverse — fair warning: things get a little creepy here — where an individual is placed in a closed room with a lethal device, like a gun to their head. The spin value of photons in the room is measured every 10 seconds — and this determines whether the device goes off or not. That basically gives the individual in the room a 50-50 chance of living or dying for every 10-second check. (If you zoom out, tying the individual’s life to a quantum state basically puts the individual’s existence in a superimposed state of being both dead and alive, similar to what happens in Schrodinger’s cat paradox.)
The suicidal experimenter can have one of two experiences. The experience under the Copenhagen model would look like certain death. As time goes on and the probability of survival is continuously halved, the inevitable becomes, well, inevitable. Under the Many Worlds model, death isn’t so easy to come by. Because there is always a world that the suicidal experimenter lives in and observation is the only way to focus on one point along the wave, there must be a point when the observer, who is also the suicidal experimenter, observes his or her own death. If not, then the Copenhagen model is the winner. If so, Many Worlds wins, but there has to be a funeral in this one.
The biggest problem here is that observing something like this happening would only prove the multiverse to the person in the room. This experiment, again, is not feasible for actual scientific research. Not to mention it’s also completely speculative, insanely dangerous, and totally unethical.
And yet if there are an infinite number of parallel universes around us, finally seeing them would be the most incomprehensibly amazing realization for any human mind to handle.