with negative energy, was when the theory is telling you,

也就是能量为负的那个根正是理论的关键
hey, there are particles and there are anti-particles,

世界上既有粒子也有反粒子
and the negative energy when properly interpreted will describe anti-particles.

负能量就是用来解释反粒子的
So the equations are very smart.

这些方程真的很神奇
The way the physics works is

在物理问题中
you will find some laws of motion in mathematical form,

你可以用数学方法得到运动定律
you put in the initial conditions of whatever,

你代入初始条件
you solve the equations, and the answer that comes,

然后解方程获得答案
you have no choice.

你别无选择
You have to accept the answer,

只有接受答案
but there are new answers besides the one you were looking for.

但是除了你要的答案还会有新的发现
You've got to think about what they mean,

你得去思考它们的意义