How to find higher dimensions

The Flatlanders are complaining about all these wierd ideas about 3 dimensions of space. They want proof. So I think I'm going to tell them this:

The speed of light and all particle interactions dependent upon photons (E&M) are confined to their 2 dimensional plane. But gravity is caused by higher dimensional processes. They need to figure out some mathematical model or phenomena that includes both. They need to test it under two conditions. First, they need to test it in normal flat paper space. Second, they need to test this mathematical model or phenomena in wrinkled space. They need to find some place in their paper universe where it's wrinkled. When they compare the differences between the two either mathematical descriptions or phenoma, then they'll have to figure out what changed. That is the first step to find higher dimensions.