Mr. Fullerton recently gave us a hand out explaining electromagnetism and how it directly relates to Einstein's Theory of Special Relativity. According to the theory, length and time are not absolute measures, but can be perceived differently based on the motion of the observer. This can be applied to current in a wire. Take a wire with no current flowing in it. As a whole, the wire is neutral as there are equal numbers of protons and electrons. When current flows through the wire, the electrons flow in a specific direction. The density of positive and negative charges in any section of the wire is the same, however, making the wire still neutral. Imagine a charged observer object moving outside the wire. The charges within the wire experience different motion relative to the charged object, so the separations of protons and electrons differ slightly from the observer's perspective, creating a difference in charge density, leading to a non zero net electrical charge, and therefore a net electric field. The charged observer sees the wire as having a net electric charge; therefore, it experience a magnetic force. It is crazy to think that the charged observer would experience a force simply because of what it perceives in the wire; even though the wire is neutral, it is not neutral to the charged observer. Crazy stuff.