As we build up light rays, the shape of the envelope begins to emerge. The only difference between this diagram and the physical system is that here, the overlap makes a dark envelope, whereas in the cup the overlap makes a bright envelope
Antigoni is a PhD student at UCL working on Boundary Element Methods for electromagnetic scattering.
More from Chalkdust

Our favourite (and not-so-favourite) Euler equations
A collection of our favourite and least favourite things named after Euler, from issue 07
Creating hot ice
We created hot ice from scratch, a solution that remains liquid even below its freezing point!
Curiouser and curiouser!
Some surprising mathematical facts
Find your perfect partner
Find your perfect partner with this wonderful tree diagram!
Menace: the Machine Educable Noughts And Crosses Engine
Teaching a bunch of matchboxes how to play tic-tac-toe
Introducing the Cuboku
Can you solve our 3D Sudoku puzzles?
