Double slit experiment - sensor interacts with photons?

[Dale]

Electron has no size? What does it even mean?

It means it is a fundamental particle. It isn’t made up of something else, as far as we can tell.

 

[bhobba]

Electron has no size? What does it even mean?

It means within experimental error it has no well defined size.

As an excitation in a quantum field it can be spread out like a wave or just at a point.

Thanks
Bill

 

[Herman Trivilino]

Electron has no size? What does it even mean?

If it had a size it would have to be composed of something. And then we'd be trying to figure out what that something is made of. Etc. Ad infinitum.

Think of peeling an onion. Every time you peel off a layer, there's another layer. Either you keep peeling layers forever or you reach a core. As Feynman was fond of saying, we don't know which way Nature behaves until we investigate.

Think of size as a property. Particles have properties like mass, size, spin, isospin, and so on. If one of those properties has a value of zero, that doesn't disqualify it from being a particle.

It's possible that the electron has size. If so, it's less than about $10^{-18} \ \text{m}$.

Similarly, if the photon has mass it's less than about $10^{-48} \ \text{kg}$.