Quantum mechanics is simultaneously beautiful and frustrating.
Its explanatory power is unmatched. Armed with the machinery of quantum theory, we have unlocked the secrets of atomic power, divined the inner workings of chemistry, built sophisticated electronics, discovered the power of entanglement, and so much more. According to some estimates, roughly a quarter of our world’s GDP relies on quantum mechanics.
Yet despite its overwhelming success as a framework for understanding what nature does, quantum mechanics tells us very little about how nature works. Quantum mechanics provides a powerful set of tools for successfully making predictions about what subatomic particles will do, but the theory itself is relatively silent about how those subatomic particles actually go about their lives.
For example, take the familiar concept of a quantum jump. An electron in an atom changes energy levels and thus either absorbs or emits energy in the form of one photon of radiation. No big deal, right? But how does the electron “jump” from one energy level to another? If it moves smoothly, like literally everything else in the Universe, we would see the energy involved change smoothly as well. But we don’t.
So does the electron magically disappear from one energy level and magically reappear in another? If it does, name one other physical object in the Universe that acts like that. While you’re at it, please give me a physical description of the unfolding of this magic act. I’ll wait.
Quantum mechanics is completely silent on how the electron changes orbitals; it just blandly states that it does and tells us what outcomes to expect when that happens.
How are we supposed to wrap our heads around that? How can we possibly come to grips with a theory that doesn’t explain how anything works? People have struggled with these questions ever since quantum mechanics was developed, and they’ve come up with a number of ways to make sense of the processes involved in quantum behavior. Let’s explore three of these interpretations of quantum mechanics to see if any of them satisfy our cravings for a “why” behind all this odd phenomenology.
The Copenhagen interpretation
If you’re not the kind of person to sweat the small stuff, the Copenhagen interpretation is for you. Like the other two interpretations we’ll explore in this article (and the many more we won’t), there isn’t one precise, definitive Copenhagen interpretation—rather, it’s a collection of ideas that share a similar set of values.
In this case, those values are best expressed as “shut up and calculate.”
The Copenhagen interpretation was named in the 1950s, but it traces its lineage to some of quantum theory’s founding figures who were based in that city in the early 20th century: Werner Heisenberg and Niels Bohr.