One atom casts a shadow
Seems unlikely that you could record the shadow of just one atom — but you can, apparently, if you use the right frequency of light. Get it wrong by one part in a billion, though, and the shadow vanishes. This isn’t just a curiosity — this sort of study should help determine the optimum conditions for microscopy, so you can use as much light as possible to observe cellular processes without destroying the cell. Read more here.