# B What does a magnetic field consist of?

1. Aug 1, 2016

### Mary Space

Of what consist magnetic field?
Someone says that magnetic field consist of photon, is it true?

2. Aug 1, 2016

### ProfuselyQuarky

I don't really think that you can say that the electromagnetic field is made of anything (in layman's terms, at least....). I see it as a constitutive "thing" that can't be described as being made out of other "things" for the very reason that it is intrinsic. And I think fields are more fundamental than particles, anyways. True, photons are associated with the electromagnetic force/waves, but they do not make of the field in of themselves.

Last edited: Aug 1, 2016
3. Aug 1, 2016

### Staff: Mentor

My limited understanding of this topic is pretty much identical to ProfuselyQuarky's. Fields are fundamental objects and are not made up of anything else.

4. Aug 2, 2016

### Mary Space

Yes but we know that all matter is composed of elementary particles, but because the field must also have its own construction
As for the photons I watched an interesting program "Through the wormhole with Morgan Freeman," and it said if I understood correctly that the photons strike the core and move to another, etc.

5. Aug 2, 2016

### davenn

neither an electric field, nor a magnetic field is made of matter

strike the core of what ?

Dave

6. Aug 2, 2016

### Mary Space

To be honest, this I did not understand, but perhaps the core of the Elements which includes a magnet.

7. Aug 2, 2016

### NTW

At the present time, lacking a satisfactory theory, both the magnetic and the electrostatic fields are temporary solutions in order to explain the 'action at a distance'. That was, too, the case of the gravitational field, until Einstein formulated his General relativity.

8. Aug 2, 2016

### Staff: Mentor

I don't see anything unsatisfactory about fields. They are extremely useful concepts that remain the simplest, most accurate way to describe much of physics.

9. Aug 2, 2016

### davenn

@Andy Resnick

can you help out here please. I have spent the last hour searching for a satisfactory answer without success

Dave

10. Aug 2, 2016

### Andy Resnick

The question isn't really a scientific question. Magnetism is a well-defined phenomenon (materials either possess a magnetic moment or are induced to develop a magnetic moment), but the concept 'magnetic field' is an artificial ('man-made', excuse the gender specificity) construct.

The basic entity in magnetostatics is the magnetic dipole; in the presence of magnetic materials, the dipole experiences a mechanical torque: compass needles orient themselves in response to magnets. Similarly to Coulomb's law, the magnetic field was initially defined in terms of force equations (Biot and Savart's law). Farady introduced the concept of 'fields' as a way to explain action-at-a-distance, but it wasn't appreciated until later than using the idea of a field gives independent meaning to B (and E), independent of the sources.

Rather than asking "what is the magnetic field made of", a better question is to ask "what are the measurable properties of the magnetic field?". Some of the properties include energy, flux, and angular momentum. Based on this, a reasonable object used to represent the magnetic field is a vector field. Photons can also be described in terms of a vector field, and so the magnetic field can be described in terms of photons.

There's a lot more to the foundations of electromagnetism, but hopefully this is a good start.

11. Oct 19, 2016

### wimax32

In my opinion, asking questions is naturally scientific. Claiming a question is "not scientific" sounds ignorant.
Field is not a concept, it's a label, it's a name given to something to explain its effects and not itself. The "field" always depends on the source and can never be manipulated without manipulating the source because we don't know what it's made of.

Things that you mentioned all are effects of a magnetic field. We also know the source creation of a magnetic field. But we don't know what it is exactly.
A good analogy would be, we know wind flow can turn a wind turbine, and we know wind is generated by thermal/pressure gradient in the air. We also know that wind is made out of a mixture of gas molecules exchanging thermal energy and kinetic energy between the source and the turbine.

But what can we say about the magnetic field. What are the carriers of the magnetic field?

Can you cite a reference for your statement, that the magnetic field is made out of photons, or the magnetic field interaction with a charged particle is through photon interaction with the charged particle?

The thing is unlike matter, where we deeply focused on its constituents and we have formulated different theories down to quarks, we stopped thinking about the magnetic field or fields in general because the current theories work and we haven't had a need to study their nature further but rather focused on their effects on other things.

12. Oct 19, 2016

### jonjacson

AN electric charge in motion creates a magnetic field... if you change the coordinate system so the particle is at rest there is no magnetic field.

13. Oct 19, 2016

To give some added emphasis to how difficult the question is try googling "Richard Feynman Magnets". It seems to me that Feynman is being a bit evasive at the beginning but then starts to get some thoughts together. Personally I like to think of the field as a mathematical construct which is informed by the observations and which enables us to carry out certain calculations such as calculating the force on a moving charged particle.

14. Oct 19, 2016

### Staff: Mentor

The scientific method is a technique for answering a certain class of questions, and it is quite appropriate to describe questions that cannot be answered using the scientific method as "not scientific" - indeed, that's close to a tautology.

It's worth comparing with what the first and greatest field theory does and doesn't do. Newton's $F=Gm_1m_2/r^2$ tells us how a gravitational field behaves, but doesn't try to answer the question of what it is "made of". Einstein's General Relativity doesn't provide an answer either; it replaces one methematical description of the interaction of nearby masses with another (more accurate and more beautiful) one, but it's still a description of how gravity behaves, not what it's made of. As with electromagnetism, we're answering questions about how the fields behave and what laws they obey, but not why or what they are made of.
(I have taken the liberty of replacing all references to the "magnetic" field with "electromagnetic", as it makes no sense to talk of a magnetic field in isolation).
Any standard text on quantum electrodynamics will cover this in great detail. It is stuff that has been well understood for better than a half-century and is a staple of any graduate-level physics program. The field is not "made of" photons, but as Andy Resnick says, it is described in terms in terms of photons.
(A very mathematical gentle introduction is http://www.physics.usu.edu/torre/3700_Spring_2015/What_is_a_photon.pdf)

15. Oct 20, 2016

### Andy Resnick

I hesitated before responding, let's see if my initial impulse was correct:

Lots of questions (and opinions) are nonscientific. The act of asking a question is not a privileged activity.

The term "field" is a label for a specific mathematical object. Electric and magnetic fields can be source-free.

The use of virtual photons to describe electrostatic and magnetostatic phenomena is well established in QED. Here's an explanation from someone with a lot more patience than I:

https://van.physics.illinois.edu/qa/listing.php?id=414

16. Oct 20, 2016

### David Lewis

Lord Kelvin conceptualized a force field as a network of Faraday lines of force that surround a field-generating body.
Fields in this sense would be imaginary objects.

17. Oct 21, 2016

### Filip Larsen

18. Oct 21, 2016

### litup

Is the angular momentum part the idea that a charged particle will swerve around a magnetic line? Or tend to swerve, perhaps going in circles around the field line if the particle is close enough?

Last edited by a moderator: Oct 21, 2016