OK, remember that I promised you eclectic. My Favorite Photograph #2 for 2016 is an image taken by Aneta Stodolna of the FOM Institute for Atomic and Molecular Physics (AMOLF) in the Netherlands of the first image of the wave structure of the orbitals of the hydrogen atom with a photoionization microscope. What? you scream, and I’ll give you that. But please pause a moment. The image is in what is referred to as pseudocolor – which is always kinda pretty. The colors follow a spectrum which indicates intensity. The point is that when I saw this image for the first time this past year, my jaw dropped. It was a something that I never expected to see. It was something that I had thought was not possible. But just the same it was exactly as physicists for generations had pictured it. It was exactly what you could create from the equations of quantum mechanics imagined by a deep mathematical graphics program like Mathematica or Matlab. So there it was staring out at me in colorful glory, and I gasped.

I should explain a couple of things. First, you may remember from freshman chemistry that in hydrogen a single electron can be thought of as swirling in orbit around a single proton nucleus. It is the simplest, and in that regard, the most elegant of atoms. Now within this context, there is a famous Gedanken or thought experiment. You imagine that you have a microscope and are trying to look at where the electron is at a particular instant in time and also determine how fast it is moving. In order to get good resolution you crank up the energy of the photons. But that means that the light is going to mess up the momentum of the electron when the light hits it. Momentum is the product of mass and velocity. So the better you resolve where the electron is, the less clearly you resolve its momentum. So there is this intrinsic paradox that the better you figure out position the worse your determination of momentum becomes.  This apparent paradox is the basis of what is referred to as the Heisenberg Uncertainty Principle. Heisenberg took it a step further, saying that there is a best that you can ever do.

For you lovers of existential philosophy, this is the same as saying that you cannot separate the observer from the observed. You cannot separte the photograph from the photographer or the viewer. Pretty deep stuff. Huh?

If you don’t follow that, I have to resort to some graffiti that I saw years ago in the physics building at Cornell, when I was a graduate student. Someone had written; “Heisenberg was here or maybe it was there.” It is uncertain where Heisenberg was and it is uncertain where the electron was.

And this leads us to the very important point that  that what there actually is is a probability distribution that tells you the probability of finding the electron “there. or her or anywhere” Phew! This probability or wave function is what the Quantum Microscope enables us for the very first time to see. You might ask, isn’t this a contradiction of your stupid Gedanken Experiment. Don’t get cross with me! The answer is no, because the Quantum Microscope measures emitted electrons. It doesn’t work the way the hypothetical microscope works.

But there is another reason that this image is interesting. That is the question of why we call it a photographic image. In our time the definition of the photograph has expanded hugely. Is this really a photograph. It isn’t after all a light picture – Talbot’s “Pencil of Nature.” Is an X-ray image from deep space a photograph? Is a thermogram or a CAT scan a photograph?