because once you take these two postulates,

因为一旦你们掌握这两个公理
you have restored the relativity principle to all phenomena.

你们就为所有现象还原了相对性原理
Okay. You've gone beyond

你们已经超越了
mechanical phenomena to electro-magnetic phenomena.

力学的范畴而进入了电磁学的现象
But you will find that you have to give up

你们会发现你们必须放弃
all the other cherished notions of Newtonian physics.

所有牛顿物理体系的原有的重要观念
Think about why.

想想这是为什么
We are saying, here is a car going at 200 miles an hour,

比如说有一辆以 200 英里的时速运动的汽车
according to me.

这是我观察到的
You get into your own car

你坐上自己的车
and follow that car at 50 miles an hour.

然后以 50 英里的时速跟着它
You should get 150,

相对时速本该是 150