Magnetism and Ampere-Maxwell's law

[e2m2a]

Magnetic fields are present in space. Doesn’t Ampere-Maxwell law state this is a consequence of currents or changing e-fields? Why in astrophysics is the emphasis on magnetic fields and no emphasis on currents and changing e-fields that cause these magnetic fields? Does modern astrophysics imply the Ampere-Maxwell’s law does not always logically apply with its converse?

For example, Newton’s second law f = ma is true, and its converse is true. If a net force is applied to an object, the object will accelerate. Its converse is also true. If an object is accelerating, then a net force is acting on it.

Now take the Ampere-Maxwell law. It states mathematically if you have a current or changing e-field, then you must have a magnetic field. But its converse is true: If you have a magnetic field, then you must have a current or a changing e-field present. That’s what the equal sign in the equation implies: If a=b is true, then b=a is true.

This being the case, again, why are currents and changing e-fields ignored in discussions of space magnetism?

 

[chrisbaird]

Yes, everything you said is true. In what type of contexts due you tend to see currents/E-fields ignored when discussing B-fields?

 

[e2m2a]

Yes, everything you said is true. In what type of contexts due you tend to see currents/E-fields ignored when discussing B-fields?

Here are two articles talking about magnetic fields in space with no reference to currents.

http://www.unisci.com/stories/20021/0109021.htm

http://www.universetoday.com/62732/magnetic-fields-in-inter-cluster-space-measured-at-last/

This is strange that currents are ignored. I believe it has to do with the known fact that enormous amount of energies would be required to keep unlike charges separated because of Coulomb's law of attraction of unlike charges. However, the presence of magnetic fields imply charges are seperated and moving as steady or transient, displacement currents to acquire voltage equilibrium. This is a fact observed by the presence of magnetic fields.

To say magnetic fields exist without currents or displacement currents is implying special relativity doesn't always hold. The E-fields of stationary charges viewed in one frame can be viewed as magnetic fields in other frames that see the charges moving.

To state magnetic fields exist without currents is saying something very strange: stationary charges can generate magnetic fields. Or, even stranger: magnetic fields can exists without the presence of any charge, stationary or moving.

 

[zhermes]

Magnetic fields are present in space. Doesn’t Ampere-Maxwell law state this is a consequence of currents or changing e-fields?

Correct.

Why in astrophysics is the emphasis on magnetic fields and no emphasis on currents and changing e-fields that cause these magnetic fields?

Just because you read two popular articles on astrophysical subjects, and they don't talk about currents, doesn't mean that astrophysics puts 'no emphasis' on them.

Does modern astrophysics imply the Ampere-Maxwell’s law does not always logically apply with its converse?

Nope.

This being the case, again, why are currents and changing e-fields ignored in discussions of space magnetism?

Probably because articles on "universe today" don't delve into the full depth of the problem. There are a myriad other issues they're 'ignoring' in their discussion as-well. In general, 'popular' science articles don't really contain any of the real 'science'.

This is strange that currents are ignored. I believe it has to do with the known fact that enormous amount of energies would be required to keep unlike charges separated because of Coulomb's law of attraction of unlike charges. However, the presence of magnetic fields imply charges are seperated and moving as steady or transient, displacement currents to acquire voltage equilibrium. This is a fact observed by the presence of magnetic fields.

False. Large magnetic fields does NOT require large scale charge separation and macroscopic net currents. Astrophysical magnetic fields are generally created and propagated plasmas, seeded from initial magnetohydrodynamic instabilities (e.g. MRI), and amplified through resonance phenomenon or dynamos, etc etc.

To say magnetic fields exist without currents or displacement currents is implying special relativity doesn't always hold.

Review maxwell's equations.

Or, even stranger: magnetic fields can exists without the presence of any charge, stationary or moving.

What is light?

 

[e2m2a]

False. Large magnetic fields does NOT require large scale charge separation and macroscopic net currents.

Why do large magnetic fields not require macroscopic net currents? What happened to Ampere-Maxwell's law? Does large make a modification of this law?

 

[zhermes]

Why do large magnetic fields not require macroscopic net currents? What happened to Ampere-Maxwell's law? Does large make a modification of this law?

Nope, http://en.wikipedia.org/wiki/Maxwell%27s_equations". Magnetic fields depend NOT on the magnitude of electric fields, but on the time-rate of change of electric fields.
https://www.amazon.com/dp/1402014333/?tag=pfamazon01-20

 

[e2m2a]

Magnetic fields depend NOT on the magnitude of electric fields, but on the time-rate of change of electric fields.

Yes, but the first term in the integral form of Ampere-Maxwell's law contains uI, where u is the permeability of free space and I is current. What happened to this first term?

When we are dealing with plasma as the conductive medium, do we ignore this term?

When you speak of large magnetic fields do you mean large as in high Tesla values or large in the geometric sense-- large magnetic loops whose diameters span light years?

 

[ttmark]

Magnetic fields are present in space. Doesn’t Ampere-Maxwell law state this is a consequence of currents or changing e-fields? Why in astrophysics is the emphasis on magnetic fields and no emphasis on currents and changing e-fields that cause these magnetic fields? Does modern astrophysics imply the Ampere-Maxwell’s law does not always logically apply with its converse?

For example, Newton’s second law f = ma is true, and its converse is true. If a net force is applied to an object, the object will accelerate. Its converse is also true. If an object is accelerating, then a net force is acting on it.

Now take the Ampere-Maxwell law. It states mathematically if you have a current or changing e-field, then you must have a magnetic field. But its converse is true: If you have a magnetic field, then you must have a current or a changing e-field present. That’s what the equal sign in the equation implies: If a=b is true, then b=a is true.

This being the case, again, why are currents and changing e-fields ignored in discussions of space magnetism?

You are correct, if the magnetic currents are being ignored in the publication you are reading they are demonstrating a lack of understanding on how electromagnetism works because if you have a magnetic field you have magnetic currents.