But that is not enough.
The world is full of things that change with time and space.
For example, an apple falling, or an author being shaken by a reader, how do they fundamentally differ from waves?
The answer is equally simple:
When a wave propagates, though its position changes at different times, its shape remains the same.
That is, if one second ago the wave had this shape, one second later, although it is not in the same position, it still has the same shape.
This is a very strong restrictive condition.
Since we use f(x, t) to describe waves, the initial shape of the wave (shape at t=0) can be represented as f(x, 0).
After time t, the wave speed is v.
The wave then moves a distance vt to the right, which means the initial shape f(x, 0) is shifted vt to the right.
Thus Xu Yun wrote down another equation:
f(x, t)=f(x-vt, 0).
Then he glanced at Faraday.
Among the bosses present, most came from professional backgrounds, only Faraday was an apprentice-born 'underdog.'
