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

Significant figures: Julia Robinson
Ashleigh Ratcliffe tells the story of another hidden woman in mathematics.
Top Ten vote issue 17
Have your say
In conversation with Chris Budd
We chat to one of the UK's most qualified voices in mathematics communication
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!
