It now seems clear that dark matter interacts more than just gravitationally. Earlier studies have hinted at this, and a new study supports the idea even further. What’s interesting about this latest work is that it studies dark matter interactions through entropy.
Entropy is a subtle and powerful concept in physics. It was first introduced as a property in thermodynamics, but it plays a role in everything from black holes to the flow of time. It’s also rather difficult to define without relying on mathematics.
For this latest work, entropy is better described in terms of how likely an object is to be in a particular state. The team used computer models to calculate the state of maximum entropy for dark matter in dwarf galaxies. The distribution of dark matter determines how strongly light will gravitationally lens. When the team looked at theoretical lensing by galactic dark matter in maximum entropy, they found it agreed with observed lensing around dwarf galaxies. Thus, dark matter seems to be in a state of maximum entropy.
This means dark matter must interact in some way. Dark matter doesn’t interact strongly with regular matter, so this study suggests it strongly interacts with itself. Without knowing exactly what dark matter is, we don’t know how it can interact. But this study and others further confirm the reality of dark matter.