As a physics teacher in the 1970s, I had access to a classroom laser. One of the many wonders that I and my students could observe was the distinctive pattern of rapidly shifting speckles—tiny bright red and black spots—when the laser’s red light illuminated a small patch of white paper or a painted wall. You can see the same effect today with a simple laser pointer.
![](https://i0.wp.com/www.sciencenews.org/wp-content/uploads/2004/09/4395.jpg?resize=300%2C225&ssl=1)
![](https://i0.wp.com/www.sciencenews.org/wp-content/uploads/2004/09/4396.gif?resize=150%2C103&ssl=1)
A laser produces light of a single wavelength, originating from a single point in space. When this light reflects from a surface that isn’t completely smooth, the waves no longer line up perfectly. These scattered waves interfere constructively (where crest meets crest) to create red spots and destructively (where crest meets trough) to create dark spots.