Everything you assume about the universe, the laws that govern it, and how objective reality works is probably wrong. What goes up doesn’t have to come down, there’s no logical reason why we can’t travel through time, and there’s a pretty good chance that you exist as one of an infinite number of doppelgangers spread across parallel universes.
That’s not stoner logic or the use of science fiction as a proxy for real science – those are actually just a few fairly tame interpretations of quantum mechanics.
Quantum mechanics is a unified theory that sets out to bridge the differences between classical physics (the kind that follow Newton’s Laws), and quantum physics (the kind that follow laws we don’t understand). Scientists have spent the past century or so trying to figure out why the two worlds don’t seem to jive when it comes to what “reality” really is.
For example, in the classical world that we believe we live in, we know that an object moving in a straight line at a speed of 100 km/h will travel 100 km in an hour. It works the same every single time. If an outside force acts upon the object, we can calculate a new rate of travel with relative ease. If we know the speed of the object and the position of the object, we can determine where it will be in the future.
Quantum mechanics doesn’t care much for time. Depending on how you interpret the scientific findings and empirical evidence that quantum mechanics is built on, time is a very fluid construct. Because subatomic particles don’t just act like regular objects – they also act like waves – we can’t make the same determinations about objects over time at the quantum scale that we do at the classical.
We cannot know a quantum object’s position and speed at the same time because, in quantum mechanics, all outcomes can be equally possible. This can get confusing when you’re dealing with infinite possibilities, so let’s break it down into just two: here and not here.
Right now you’re you and the things you see seem to exist. The screen in front of you is real, as far as you can tell. But your classical perspective limits your understanding of reality to those things you can sense, experience, and cognate. According to the Copenhagen Interpretation of quantum mechanics, that screen is only here because you observed it. The myriad positions that an object’s waveforms can ultimately take are like unformed predictions waiting for someone like you to come along, take a measurement (by simply observing), and cause the universe to will forth the object’s reality. Basically you’re a god; you determine what’s real by virtue of your existence and observations.
Maybe you don’t want to believe you’re a god. Perhaps you’re more comfortable with the idea of reality being real whether people are around to observe it or not. That makes sense right? That’s basically the de Broglie-Bohm/Pilot Wave interpretation. This interpretation is deterministic – it says everything was already going to be what it ends up being and there’s never been any ambiguity about it. It requires no observers, so in this model our existence is pointless. Whatevs.
Perhaps that’s why another interpretation, the Many Worlds theory, is having a resurgence in popularity. The Many Worlds theory is the opposite of the Pilot Wave one: it says that every possibility is real and manifests across infinite universes. You’re alive in this universe, dead in another, Rick in the next, and Morty in the fourth. All things are not only possible, but definite in a reality with infinite universes.
And that brings us to my personal favorite: the one that says “you’re not a god, I am.” I’m referring to the Ensemble Theory. This one says that all things are possible, but only one outcome shall manifest. The universe itself prepares an infinite number of systemic possibilities – series of events that will lead to the eventual reality – and keeps them hidden until the observer (that’s me) makes a measurement. It’s like the universe is a restaurant with a menu that has infinite items that are always prepared, and it’s happy to serve me whichever one I desire in any given moment.
Though, I suppose it could be your universe and I’m just an object lucky enough to have been observed. In which case, thanks!
There are other interpretations, but these are among the most pervasive and popular in the physics world. It’s worth mentioning that, while these theories are definitely wacky, they also represent the collective knowledge our species’ smartest, most determined scientists have managed to come up with over centuries of study.
There’s no simple, boring theory that ties the quantum and classical world together in a manner as successful (and resilient to scientific rigor) as quantum mechanics and its many interpretations.