March 21, 2018

Link: Is quantum physics weird, or is it just us?

Physicist (and Forbes contributor) Chad Orzel posted an interesting article today:

Why Do We Think Quantum Mechanics Is Weird?

Some snippets:

...If the universe is really governed by quantum rules, why do those rules seem so strange to us?

The answer is basically right there in the definition of "weird": quantum physics seems weird because it runs counter to our everyday intuitions about how the world works.

... there isn't really a difference in the rules that apply for big objects and the rules that apply for small ones-- the universe is quantum on every scale. The "classical rules" that we see are just the result of quantum physics when applied to really big things.

...when you study the behavior of huge numbers of objects whose individual interactions are described by simple rules, you often find that the collective behavior of the large system seems to be described by another set of simple rules, rules that aren't necessarily obviously related to the original interaction rules. This idea of high-level rules emerging from lower-level ones leads to the hierarchical structure of sciences-- chemistry is the physics of too many atoms, and biology is the chemistry of enormous numbers of molecules, and so on.

In a sense, that's what's going on: when we apply quantum mechanics to enough particles to make up a visible object, the particles and their interactions are all governed by quantum rules, but the collective effect is to give the appearance of a different set of rules that we call "classical." Everyday reality is just what happens when all those quantum properties blur together. ...

This is an interesting principle, and if you think about it a moment, it applies to lots of things besides quantum physics. You can know everything about electronics and still be unable to get a smartphone app to work right. A neurology PhD won't help much in predicting election results. The larger-scale phenomena have rules that must be related to the underlying phenomena, but are completely non-obvious — and, vice versa, understanding your smartphone app gives you almost no clue about the underlying electronics.

I think this also gives us some insight into what we call "common sense". We're biased towards explaining things and making decisions based on our experience and knowledge. Where we lack direct experience and knowledge, we frequently extrapolate from what we're familiar with. That's risky even under ideal circumstances. But what about the cases where we're extrapolating to a higher-level or lower-level phenomenon? Those levels may have their own rules, of which we may be ignorant. You can use a carpenter's square to mark off the wood for the house you're building, but you can't extrapolate that technique to lay out surveying lines for a whole country, because the Earth is round. You can (maybe) save your kid from hard drugs by taking the drugs away, but you can't scale that up to a national level without facing a bunch of social, criminal, and economic effects.