What is free electromagnetic field?

[sergiokapone]

Maxwell's equations solutions in vacuum - is a free electromagnetics waves.
Such solutions can be obtained even without knowing anything about the charges and currents. Does this mean that such waves is the essence , not related charges, e.g. free electromagnetic waves?

Moreover, the Maxwell's equations with ##\delta##-shaped sources also give the solutions, that looks like free electromagnetic waves, but in a far (wave) zone. Sometimes it is said that it is a field that is off the charge , but its amplitude is uniquely determined by the motion of the sources .

Is it possible to think that there are waves that are generated by charges , and others which exist independently?

 

[Jano L.]

Is it possible to think that there are waves that are generated by charges , and others which exist independently?

Yes, total field can be though of as sum of retarded fields of close-by particles and the background field. The background field can be thought of as having no sources, or as having very distant sources.

 

[sergiokapone]

The background field can be thought of as having no sources

Did I understand correctly, if we imagine the world with no charges, for example, the EM-waves will still exist?

 

[dextercioby]

The classical e-m field is created by classical sources. The <free Maxwell fields> are a useful approximation, especially when going into quantum mechanics.

 

[sergiokapone]

Ok, thanks for all.

 

[mikeph]

Did I understand correctly, if we imagine the world with no charges, for example, the EM-waves will still exist?

There are two questions here. Do free-space solutions to Maxwell's equations exist? (Yes) Will they exist in a spacetime that has never contained any charges or currents? (No)

 

[sergiokapone]

Will they exist in a spacetime that has never contained any charges or currents?(No)

But it does not follow from the Maxwell's equations.
Therefore , the answer is "no" - a hypothetical.

 

[sergiokapone]

The answer rather "may be not, but it is possible"

 

[Jano L.]

Did I understand correctly, if we imagine the world with no charges, for example, the EM-waves will still exist?

Mathematically, it is possible to have non-vanishing EM field without electric charge anywhere.

 

[HomogenousCow]

Only if you have non-zero boundary conditions. Which then makes the problem, incomplete in a sense.

 

[zoki85]

Neutron-antineutron annihilation creates gamma rays. Can we conclude from this, the neutron is composed of charged subatomic particles ("quarks")

 

[zoki85]

*Bump*
:)

 

[Vagn]

Neutron-antineutron annihilation creates gamma rays. Can we conclude from this, the neutron is composed of charged subatomic particles ("quarks")

No, electron-positron annihilation also produces gamma-rays but there's no evidence that electrons and positrons have any substructure.

 

[zoki85]

No, electron-positron annihilation also produces gamma-rays but there's no evidence that electrons and positrons have any substructure.

You didn't understand the question