I was sorry to miss this Q/A session on Reddit with Jena Meinecke, a researcher at the National Ignition Facility (NIF). NIF is probably best know for its research of laser confinement fusion but they actually run all sorts of different experiments.

One fact Jena mentions that I find quite remarkable is the scale-invariance of magnetohydrodynamics. Scale-invariance means we can create tiny scale models of supernovae and expect them to behave the same as a life-size one!

This is typically not the case in science. Usually when you scale something up or down things behave very differently. A beautiful example comes from biology in the form of the square/cube law, or why you can’t have a duck the size of a horse.

The idea is that an object’s mass depends on its volume whereas the bones that support that weight depend on their cross-sectional area. Now if you take a duck (smallish) and double its dimensions you will find you’ve increased its mass by a factor of 8 (because its length width and height each double) whereas its bones cross-sectional area only quadruple (because areas are 2D). So now the bones are under twice as much mechanical stress. As we scale the duck up eventually its bones cannot support its weight. Yes that’s a horrible image. And that’s why ducks are small.