Laws of physics state that when current (electricity) passes through a wire, it will create an electric field around it. The more current, the larger the electric field will be.
If at the same time you place another wire (I.E. network cable) near the field, it is likely to 'pickup' noise from that field and possibly create abnormal current patterns on it.
Because we want out network cable to be immune to these effects, the twist was introduced, effectively canceling any interference picked up by any wire in the pair.
This was first published in October 2003