[hansbo]

So a proton can emit a positron. Does that mean that the positron is somehow "part" of the proton? Does it mean that their wave functions interact in some specific way? Is there another reason?

Quantum physics has always bothered me, personally, since I find it difficult to understand reasons. Not philosophical reasons, I am fine with axioms and foundations to models, but rather intuitive reasons why it works a certain way. I know it is an extremely strong theory which makes unexpected, later confirmed, predictions, but there is a frustration that the only explanation to things is "math".

[XorNot]

Sort of? But it's less "there is a particle doing things" and more "there's a probability field which can describe a particle doing something" (alongside a bunch of other probabilities it interacts with).

One of the ways you can calculate the probability of nuclear decay for example is to assume that the particle you expect to see is literally existent and trapped inside a potential well defined by the atomic nucleus and then calculate the probability it tunnels out of that to free space.

The thing is "why" does get pretty anthropic: protons match electrons because we observe them to, and then on top of that we observe nuclear decay causing the conversion of a proton to a neutron + a positron (within the limits of our instruments) - so our model predicts that these are in fact the same value, and we keep measuring to check that they converge in that direction (it would be a big deal, for example, if we discovered this wasn't the case - every physicist would love to find out that proton charge and electron charge are actually slightly different).

[nyssos]

> Does that mean that the positron is somehow "part" of the proton?

No, and the standard intuition that there are discrete things made out of smaller parts breaks down when you look closely enough. The proton is a bound state of the quark and gluon fields, but it only "contains" individual quarks and gluons in a loose heuristic sense, and positrons are a different thing entirely.

> Does it mean that their wave functions interact in some specific way?

Yes, or more precisely it means that the quark fields interact with the electron field (free electrons and positrons are different states of the same underlying bispinor field) and the W boson field in some specific way.

> Quantum physics has always bothered me, personally, since I find it difficult to understand reasons.

Ultimately, the sort of mechanistic explanations you're looking for do not exist: the universe runs on differential equations and linear algebra, not billiard balls and clockwork.

[Koshkin]

> Does that mean that the positron is somehow "part" of the proton?

A photon turns into a (virtual) electron-positron pair. Does it mean that the photon consists of these particles?