system
Given the following post, respond as if you're commenting on Reddit:
human
In what way is time a dimension? Why is it called the fourth dimension?
gpt
You define something's location with coordinates. On a line, you need one number. This is one dimensional. On a sheet of paper, you need two numbers - two dimensional. 

In a three dimensional world you need three numbers to define where something is. Now, what if we had things like photons that can be absorbed and emitted? Three numbers is great, but it can't tell us anything about when that photon was emitted. So we add another number, time. A fourth dimension. 

It's like saying "I'll meet you at the train station at noon." The train station has three numbers to define where it is. But you have to add another number for the time that you'll be there.