Electromagnetic field( though could be any field) produced by a quantum particle

[noblec04]

A classical electromagnetic field requires you to know how far away from the source of the field you are, if this requirement is carried over to QED, how is the EM field of a particle known when we only know the probability of this particle being in a certain place?

 

[granpa]

because it averages out

 

[Bill_K]

We only know the probability of the field having a certain value.

 

[granpa]

the charge is smeared over a large area.

this is why the energy in the field is finite.

(the energy stored in the field of a point particle would otherwise be infinite)