I read this article, and I'm confused about several things. http://scitation.aip.org/content/aip/magazine/physicstoday/article/57/5/10.1063/1.1768672 [Broken] Apparently, light can have orbital angular momentum as well as spin. But I don't see how this is possible, at least in vacuum. Is this in vacuum or a waveguide? (It wasn't too clear in the article or first reference) To have orbital momentum, one has to orbit around something. What is light orbiting around? The article says the center of the beam, but there's nothing there, right? I see there are various modes for Gaussian beams called Laguerre-Gaussian modes. Do these exist in free space or only in some kind of laser resonator?