Once the particles or cars reach a critical density, gridlock happens.

一旦微粒或汽车达到临界密度，就会发生交通堵塞。

Above the critical density, any additional vehicle reduces the number of cars per second passing through a given point on the road.

在临界密度之上时，任何额外的车辆都会降低 每秒通过路上某一点汽车的数量。

There's a critical density after which small behaviors from drivers can start to seriously jam up the road.

有一个临界密度，之后驾驶员的小行为可能会开始严重堵塞道路。

But once the number of cars on the road exceeds a critical density, generally when cars are spaced less than 35 meters apart, the system's behavior changes dramatically.

但是一旦路上车辆的数量 超过临界密度时，一般来说指车距小于 35 米，整个系统的行为 就会发生巨大变化。

The third option is that gravity is just right critical density is the cosmologists' term for it and that it will hold the universe together at just the right dimensions to allow things to go on indefinitely.

第三种可能是，引力恰如其分就是宇宙学所谓的临界密度它把宇宙控制在一个恰当的范围，使事物永远继续下去。