This article has an image showing the 2S and 2P states of a hydrogen atom. The caption makes the following claim:

The 2S and 2P states of hydrogen show where the electron could be found at any given time. These images show the possible locations of the electron in each state; the proton, unmarked, is at the center of each image. In the 2S state, the electron overlaps the proton, and for a non-zero amount of time, the electron is inside of the proton itself. In the 2P state, the electron and the proton never overlap.

My question is about the statement

for a non-zero amount of time, the electron is inside of the proton itself

It doesn't make sense to me that the electron could be inside the proton. Does that actually happen, or is this a simplification?

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    $\begingroup$ The 1s (and 2s, ...) electron wavefunction is non-zero where the proton is. However, I prefer to not think of the electron as a tiny ball zooming around where the wavefunction suggests it might be, so I disagree with how the article is worded. But, yes, electron capture processes rely on the overlap... $\endgroup$ – Jon Custer Sep 11 at 16:59
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    $\begingroup$ Why do you think it can’t happen? A proton is just a bound state of quarks held together by gluons. It isn’t impenetrable. $\endgroup$ – G. Smith Sep 11 at 17:20
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    $\begingroup$ Related: physics.stackexchange.com/q/20003/2451 , physics.stackexchange.com/q/9415/2451 , physics.stackexchange.com/q/105400/2451 and links therein. $\endgroup$ – Qmechanic Sep 11 at 17:36

Electrons are quantum mechanical entities, elementary point particles in the Standard model of particle physics, thus obey quantum mechanical laws.They are described by a probability distribution for their location, given by $Ψ^*Ψ$, where $Ψ$ is the wavefunction, a solution of the quantum mechanical wave equation describing the particular atom. ( I suppose it is hydrogen)

The proton is not elementary, it is a composite of elementary particles, the three valence quarks and a sea of quarks antiquarks and gluons, a very busy place . There is no conceptual problem for the electron to be found alongside if measured, except for how to measure it!

Electron capture in nuclei where there is enough energy to turn a proton into a neutron is the closest one can demonstrate experimentally that the electron can be in a complex environment and be captured to create a neutron plus an electron neutrino (to conserve lepton number). See also here.


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