Talking about both photons and electrons. Uncertainty principle is about position and momentum, but electron is considered wave?
We have mathematical model of light being EM Waves, what does it being particle even mean?
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Light and electrons are two good examples because they get at the problem from different directions.
Let’s start with light. It started out as obviously a wave based on the physics being developed by the big greats of electromagnetics, culminating in Maxwell’s equations that you might have heard of. The core math of light is definitely that of a wave, and that classical wave model predicts almost everything light does: propagation, refraction, reflection, polarization, interference, etc. It’s not important that we go into all those things, just that you understand that they’re inherently wave-based, and light does all of them.
Until light hits something and gets absorbed, that is. Absorption (and emission) is where the wave model fails completely, and where the particle side of the duality shows up. Energy from light can only get absorbed in discrete chunks, which we call photons. We’re good at detecting very low quantities of light, so we can actually build devices that see each individual chunk getting absorbed from very weak light sources hitting them. I mentioned interference above, and this is where it gets wonky. You can have interference by sending light through two narrow slits, and the pattern the light makes will end up with light bars with dark spaces between them. But, do this with the photon-counter, and you see each individual hit as it happens. Wait long enough, and the pattern still emerges, built up from each individual hit. So even though the energy is still in individual chunks, it follows the wave rules for how it should move through and past the slits. Weird.
Then we have electrons, which were very much thought of as particles. There’s a bunch of them around atoms, we can see them move around with electricity, they have mass, lots of the original EM work on electrons was very much that they are a particle.
Until someone tried putting them through that double-slit experiment like they did for light, *and the electrons behaved just like the light did*. They made the same interference pattern, showing that they, too, followed the wave rules. So now light is both wave-like and particle-like, and electrons are both particle-like and wave-like. Even weirder!
This was expanded to *all* particles, though doing the interference experiment with larger particles gets much harder, but the math checks out.
We know all of this very well by experimentation, as the quantum mechanics theories that predict it are the most verified theories in the history of science. But your guess is as good as anyone’s as to why, or how to answer the question of “is it a particle or a wave.” Both, neither, sometimes one or the other. I’m convinced we still don’t yet have the full story.
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