What's the next difficult thing?

那么更难的会是什么
The next difficult thing

更难的就是
is to consider motion in higher dimensions.

要考虑更高维的运动
How high do you want to go?

你们希望有多高的维度呢
For most of us, we can go up to three dimensions

对于大多数人来说我们最多可以考虑三维
because we know we live in a three-dimensional world.

因为我们生活在一个三维世界
Everything moves around in 3D.

所有的物体在三维中运动
That'll be enough for this course.

那对于这门课来说已经足够了
In fact, I'm going to use only two dimensions for most of the time

实际上大多数时候我只考虑二维的情况
because the difference between one dimension and two is very great.

因为一维和二维的差别很大
Between two and three and four

但二维三维和四维
and so on is not very different.

以及其它维数间的差别就不那么大了