虽然电子都是带负电并互相排斥的，但它们穿过金属时所抛弃的正离子可以在某种限制性条件下（比如冷却该金属）成为两个电子互相吸引的有效媒介。
Although electrons are negatively charged, and therefore repel one another, the positive ions that they leave behind when they flow through a metal can mediate an effective attraction between two electrons under restrictive conditions (for example, the metal must be very cold).