Why does the gravity model work?

We develop theories and models by observation - empirical facts. Then we try to find ways (often mathematical) to describe those observations. The real test of a model that "works" is by using it to predict some phenomenon that we have not yet observed and then observing it. Any model or theory is only as good as its descriptive and predictive ability in application to observations.

The "Gravitational Lens" effect is one of the primary evidences supporting the gravity model, as it was anticipated by theory before it was observed.

The gravity model works because it is based on the principle that larger entities have a greater gravitational pull and therefore attract more interactions, such as trade, migration, or communication. It also takes into account distance, as interactions tend to decrease as distance increases.