Why can't a physicist make quantum physics understandable to the average person?
This is a question that gets asked a lot, sometimes querulously, sometimes suspiciously, as if we were all engaged in some kind of conspiracy against "average people", keeping our secrets from them so we can lord it over ordinary folk with our superior knowledge of wavefunctions and stuff.
The reality is far worse: the reason why we (physicists) can't make quantum mechanics understandable to ordinary people is because quantum mechanics describes the world, and the world is not understandable to ordinary people. Truth be told, it isn't understandable to extraordinary people either. It isn't "understandable" at all, in the technical sense of "understandable" that has been used by philosophers for more than two thousand years.
To understand why, we need to understand what we mean by "understand", and how far reality is beyond comprehensibility.
Max Born, one of the founders of modern quantum theory, said, "Somewhere in our doctrine there lurks a conception not justified by any experience, which will have to be eliminated in order to clear the way." Daniel Greenberger summed it up more pithily many years later: "Quantum mechanics is magic." He was not entirely wrong.
A considerable fraction of the people who have studied quantum mechanics seriously have become mystics. Not fake, "send me $2.95 and three box tops and I'll send you the answer to the mystery" mystic, or full-Deepak quantum scam artists, but people who genuinely believe there is a mystery at the core of our existence that we are unlikely to ever solve (although that won't stop us from trying.)
And to be clear: I am one of those people.
The problem is that reality is described by Schrodinger's equation, which describes the smooth, causal evolution of a continuous function--the wavefunction--that never "collapses" or "jumps" or does anything similar. But Schrodinger's equation describes a reality that can be in multiple contradictory states at the same time. It tells us reality--at least the unknowable bits--are contradictory, which is by definition incomprehensible.
Non-contradiction is literally what defines "reality" as we normally talk about it. Twenty-five hundred years ago Aristotle wrote what is now called the Law of Non-contradiction: "A thing cannot both be and not be the same thing in the same respect at the same time."
He identified this as "what could be said of anything that could be said to be." If a thing exists, according to Aristotle and most philosophers who came after him, it must be possible to describe it in a non-contradictory way.
But Schrodinger's equation describes contradictory situations in (unknowable) reality: a particle that runs into a potential barrier can both be transmitted through it and reflected off it in the same respect and at the same time, for example. We only ever measure one of these contradictory outcomes directly, but indirect experiments allow us to infer that both of them occur, because they can be made to create observable interference patterns in the results of measurement. The knowable world, revealed by measurement, obeys Aristotle's dictum, but there is an absolutely unknowable world, hidden behind the quantum veil, that does not.
Somehow--no one knows how--the classical, non-contradictory world arises out of this contradictory, unknowable, substratum of existence. The process by which this happens is weird. It violates our every intuition, right down to Law of Non-contradiction, because it is profoundly non-local: any two particles that have interacted remain "entangled" in such a way that when we measure one of them, we create a state such that any measurement on the other one will be consistent with the first measurement, no matter how far apart they are.
For example, say two electrons scatter off each other in one dimension, which means they move toward each other along a line and then (in accordance with Schrodinger's equation) both bounce off each other and pass through each other. But their state remains entangled such that if we later on measure one as having bounced off, we can only ever measure the other having bounced off as well. Anything else wouldn't conserve momentum, and to the considerable surprise of philosophers, physical conservation laws governing momentum and energy are more general and powerful than the laws of logic.
Beyond the Law of Non-contradiction, the Law of Local Causality says that what a thing is now causes what it does now. But for entangled particles (which is all particles that have ever interacted with anything) there is no definable "now" that can be used to make this law meaningful, because "now" is something that can only be defined locally, in accordance with Einstein's special relativity. For far-separated particles, there is no consistent way to define which one is measured first, for example, making it impossible to talk about a measurement on one particle "causing" the other particle to fall into a particular (consistent) state.
So how do we even talk about such things? We have mathematical language that lets us calculate probabilities, but we do so by averaging over the world we cannot see and cannot comprehend. We have some heuristic models that different physicists use to think about the intermediate stages of the calculations, but if you get a couple or three physicists talking about how they do this over a beer you'll likely get two or three (or more) different answers. There is no consistent way to think about non-local phenomena, because they violate the logical criteria required for consistency.
This is why quantum mechanics is hard to understand: it describes a reality that violates the conditions that define "reality" insofar as reality can be made comprehensible to us. We can never directly observe that unknowable reality, where contradictory outcomes exist side-by-side, and this fact of unknowability is critical to the workings of the theory. If what happened beyond the quantum veil was not unknowable but merely unknown the laws of logic would still prevail and the vital contradictions our existence depends on could not occur.
Fascinating Tom, and beautifully articulated for the lay person. You’ve got me interested in learning more 👍🏻
I kind of think I understand …which makes me suspicious that I am deluding myself …but anyway, thank you!