甚麼導致磁場的出現？

我也問過類似問題。
答案和virtual photon有關，但我不知道甚麼叫virtual photon.

2010-03-17 17:57:20 補充：
似乎沒有人能準確地答：

有磁場的空間，和沒有磁場的空間相比，前者多了的是甚麼東西？

1.Moving of charges can create a magnetic field.
2.The spining of charged elementary particles can produce magnetic field.i.e., the spining of electron

The "virtual photon" concept is only used to explain electromagnetic force in the quantum mechanical way, but not to explain how magnetic field is produced.

In fact, classical electrodynmaics has already explained the origin of magnetic field. Maxwell's Equations describe that a changing electric field or a flow of charges can produce a magnetic field. Permanent magnets, electromagnets or the like are all due to flow of charges.