Infinite range of E-M field vs finite age of particles

  • #1
nomadreid
Gold Member
1,408
134

Main Question or Discussion Point

It is said (hopefully no need to give references for such a common statement) that the electromagnetic field of a given charged particle is infinite in range (albeit converging to zero as the distance goes to infinity). However, given that charged particles apparently did not exist at the beginning of the expansion of the universe, and that the electric field expands at the speed of light modulo being carried along by the expansion, that the field would be finite? (I am assuming the universe having started out as already very large, possibly infinite.)
 

Answers and Replies

  • #2
phinds
Science Advisor
Insights Author
Gold Member
2019 Award
15,933
5,642
I believe that the "infinite extent" of charged particles' electromagnetic fields as well as that of the gravitational field of massive bodies are Classical Physics statements (and therefore assume a static space-time)
 
  • #3
Drakkith
Staff Emeritus
Science Advisor
20,746
4,457
The field is actually the fundamental object in modern physics, not the particles. So the field existed before the particles.
As a technical note, particles are modeled as excitations of their underlying fields in modern quantum theory (specifically quantum field theory). So photons are excitations of the EM field, electrons are excitations of an electron field, etc.
 
  • #4
phinds
Science Advisor
Insights Author
Gold Member
2019 Award
15,933
5,642
The field is actually the fundamental object in modern physics, not the particles. So the field existed before the particles.
As a technical note, particles are modeled as excitations of their underlying fields in modern quantum theory (specifically quantum field theory). So photons are excitations of the EM field, electrons are excitations of an electron field, etc.
While I agree w/ what you say, I still think that the "infinite extent" is a Classical Physics statement (and in practical terms is just a mathematical convenience anyway)
 
  • #5
nomadreid
Gold Member
1,408
134
The field is actually the fundamental object in modern physics, not the particles. So the field existed before the particles.
As a technical note, particles are modeled as excitations of their underlying fields
From what I understand (which is too little), the field of which a particle is the excitation of is distinguished from the field which is the object of the effect (attraction/repulsion) of one charged and/or massive particle on other (test) particles in space. The former is infinite, but I am referring to the latter.

the "infinite extent" of charged particles' electromagnetic fields as well as that of the gravitational field of massive bodies are Classical Physics statements (and therefore assume a static space-time)
And hence invalid, so my idea about a finite field is not off the mark?
 
  • #6
phinds
Science Advisor
Insights Author
Gold Member
2019 Award
15,933
5,642
And hence invalid, so my idea about a finite field is not off the mark?
If it is "invalid" I think it is only "invalid" in the same sense that Newtonian Gravity is invalid. They both work just fine except in extreme cases.
 
  • #7
nomadreid
Gold Member
1,408
134
If it is "invalid" I think it is only "invalid" in the same sense that Newtonian Gravity is invalid. They both work just fine except in extreme cases.
In other words, an E-M field emanating from an electron is "infinite for all practical purposes", i.e., very big (albeit finite, if one wishes to get picky)?
 
  • #8
phinds
Science Advisor
Insights Author
Gold Member
2019 Award
15,933
5,642
In other words, an E-M field emanating from an electron is "infinite for all practical purposes", i.e., very big (albeit finite, if one wishes to get picky)?
Yeah, I think that's it. As I said, I've always thought of the "infinite range" as just a mathematical fiction for all practical purposes, but then I'm an engineer, not a physicist.
 

Related Threads on Infinite range of E-M field vs finite age of particles

  • Last Post
Replies
2
Views
2K
  • Last Post
Replies
3
Views
989
  • Last Post
Replies
9
Views
4K
  • Last Post
Replies
9
Views
9K
Replies
8
Views
6K
  • Last Post
Replies
5
Views
6K
  • Last Post
Replies
10
Views
2K
Replies
1
Views
1K
  • Last Post
Replies
1
Views
2K
  • Last Post
Replies
2
Views
2K
Top