“Draw me an atom”
This amazing gif by xverdxse is close to my idea of what an atom looks like. Far from the schoolbook picture of a clump of snooker ball protons and neutrons encircled by hoops of electrons the real picture of an atom is more like a vibrating cloud. A cloud? Yeah, a specific type of cloud called a probability density function. Woah maths alert! WEEOO-WEEOO, code red, code red!
A probability density function (PDF) is just a measure (function) of how likely it is (probability) to ‘find’ the atom in a given region of space (density). The thickness of the cloud in a small region is proportional to the likelihood of finding the atom centered within that region. In the image above, it is most likely to be found in the center of the black region, and the likelihood of it being found further away gets smaller and smaller until it’s nearly zero outside.
Every frame of this image corresponds to making a single measurement of it’s position. If it weren’t on a loop and we waited long enough, we should expect it to sooner or later make a large jump to a grey or even white area.
This is how quantum tunneling works: a particle confined to a domain will at any given time have a small but finite probability of being found outside its confinement region! Even a tennis ball has a finite (but astronomically tiny) probability of tunneling through a solid wall.
So what do atoms actually look like? Well, they don’t. They area collection of volumeless point-particles that don’t have any physical shape that you can draw on a piece of paper. However they have an effective shape that is described by (amongst other things and depending on what kind of measurements you make) the PDF.
If you take a step back from your screen and look at the above ‘atom’, you can kind of consider it as a single solid entity even though it is an amorphous cloud of pixels. This is all we can say about the ‘true’ shape of the atom and is a visual approximation we have to make if we want to try to understand what atoms look like and not chew off our own faces in philosophical frustration.
This is one of the most informative posts that I’ve read in a long time. Thank you for writing it.