What is it that constitutes a magnetic field? Electrons?
virtual photons?
Incidentally,
should be
Wisest is thou who knowest thou dost not know
I knew I didn’t know that…
The original question is similar to the one which asks whether nature is inherently mathematical or whether mathematics is just a useful invention of man. If you think math is just an invention then you have to confront Wigner’s bon mot as to:
“the unreasonable effectiveness of mathematics in the natural sciences.”
Fields carry energy and momentum so for my money they must be real, especially since your only alternative would be to say that virtual particles have an independent reality.
The most complete descriptions of (non-gravitational) fields currently available are the various quantum field theories (Quantum ElectroDynamics for EM fields, Quantum ChromoDynamics for Weak fields, etc.). According to such models, fields are due to the action of virtual particles being exchanged between the interacting particles. In the case of electromagnetism, the virtual particles are photons.
No, these theories are not complete, but that’s in the same sense that no scientific theory is ever complete. We’re still very confident about them. QED, for instance, makes predictions which have been checked (successfully) to over 20 decimal places, which is better than any other theory in physics. So, yes, I’d say that virtual particles are a definite, real, physical phenomenon.
Here’s a quote I copied from somewhere or other that you might find interesting. I don’t have true cite so take it for whatever you think it’s worth.
"I think we have to be careful about virtual particles because they appear in perturbation expansions when you solve relativistic quantum mechanics for high-energy cases, and there’s really no physical motivation for them
that I know of outside of Feynman diagrams. You can solve Dirac’s equation exactly for the hydrogen atom and other systems, and that in no
way introduces virtual particles, although particle number still isn’t necessarily conserved when you solve for the current in the usual manner. So in that sense, it’s not clear that they’re any more fundamental than they would have been in non-relativistic quantum mechanics.
The virtual particles are Green’s functions, the propagators that appear in an expansion. Similar techniques are used in many-body quantum mechanics where we imagine an electron really is lifted
from the Fermi sea, knocks around in any of infinite possible ways, and then falls back or is measured. But going from that to a physical reality of virtual particles is argument by analogy, which is never very sound.
In reply to a correction in my sig,
Very well then…
Can anyone please describe a photon to me?
Doesn’t the term “magnetic field” merely mean the force that a magnet exerts on another magnet or magnetic material in its vicinity?
En garde. Bertrand Russell, An Outline of Philosophy:
Physics is mathematical not because we know so much about the physical world, but because we know so little: it is only its mathematical properties that we can discover.
fixed coding - DrMatrix
Not “merely.” Fields have independent existence and are not merely the interaction between two pieces of matter.
Here’s the main reason we say so: if you wiggle a magnet, pieces of the magnetic field break off and fly away at the speed of light. We know them as radio waves (or, if the magnet is
wiggled REALLY fast, they could be microwaves, IR, or even
visible light.)
Light is nothing but fields! (or contrarywise, magnetic fields are nothing but photons.) Electromagnetism is like a “stuff” that can move from place to place. Do we say that light has independant existence? If so, then magnetic fields have independent existence too. And so do the electric fields surrounding an “electret” or surrounding a charged object.
Here’s another way to say it: if you’ve heard about “wave-particle duality” in quantum mechanics, then you should understand that the “waves”-part involves fields. If you accept that particles exist, shouldn’t you accept that waves (and fields) also exist?