*I’m spending this week in Waterloo, Canada, attending talks at the Perimeter Institute as part of the PASCOS conference (short for particles strings and cosmology). The videos and slides from all of the talks are posted here online each day.*

It’s a pretty remarkable feature of the world we live in that the physics can change depending on how closely we look. More precisely, the strength of an interaction (such as electric force, or the strong force) can change with the energy scale used in experiments to probe the physics. Higher energy scales correspond to shorter distances, and so the physics of our world depends on how far we’ve zoomed in to nature.

For example, the charge of an electron increases with the energy scale. The equation that describes how it changes is called the Callan-Symanzik equation (a special case of the renormalization group equation), which says where g is a coupling constant like the electric charge and is the energy scale. The key is , the famous beta-function that can be calculated from quantum field theory.