Miguel Morales at Ars Technica is beginning a new introductory guide on quantum mechanics, one he promises won’t require any math. If you’ve watched some of us wrangle over the implications of QM and wondered just what the heck we were so worked up about, this looks like it will be a good series for coming up to speed.
This first entry focuses on the standard double slit and interferometer experiments. They’re clearly explained, so don’t let the jargon like “interferometer” throw you. This initial entry establishes the wave / particle duality, not just of light, but all quantum objects, including matter.
A cool line I’ll have to remember:
This is the fundamental mystery of quantum mechanics: particles move like waves and hit like particles.
The article also begins to show why the easy simple solutions that everyone initially reaches for when they first learn about this stuff, aren’t tenable:
But which path did the particle really take? The experiments show that the particles really take both paths. Despite much confusion (even among some physicists), this is the answer. But the question is based on a faulty mental image. The question assumes that a particle is really a little ball bearing, and thus must have chosen one path or the other. But this mental image is wrong. Particles really behave like waves when in motion. Asking which path a tsunami wave took when traveling between Hawaii and California really makes no sense—it is spread out. Similarly, asking which path the particle really takes makes no sense; it moves like a wave so it naturally takes all of the available paths.
Nor can we hope that this is just something that applies only to elemental particles:
Neutrons are also interesting because they are composite particles—a neutron is made up of three quarks. Even though it is made up of sub-particles, it still moves like a wave. Modern experiments have taken this much farther and regularly send Cesium atoms (more than 180 protons+neutrons+electrons), and even large molecules like Bucky Balls (60 atoms) and phthalocyanine with thousands constituent particles through similar interferometer setups. Even these huge composite particles move like waves and produce the telltale stripes in an interferometer.
Morales promises, in addition to not requiring any math, that he won’t get into the more philosophical aspects, so you don’t need to worry about being sold a particular interpretation. It looks like it will be a good opportunity to just learn the basics and begin forming your own opinions.
So far it’s pretty basic stuff, so if you’re already familiar with QM, it might not be worth your time. Although I’ve found going through these things, I almost always pick up new information.