Within Kuhn's philosophy of science, a paradigm is an exemplar of good work that others in the field copy. In essence, it works like this:
- Someone does a some specific analytical work on a problem in a given field.
- Other people working on the same or similar problems look at #1 and think: "Wow, that was impressive and successful. We should all do work like that."
- People start applying the tactics of #1 to their own work; start measuring the value of other people's work by the standards of #1; start training students to do work in the style of #1
When we get to stage #3, the research done in #1 has become the paradigm of how all work should be done in the field, enforced and imposed by the body of researchers working in that field. This doesn't mean that everyone is doing the same research; it means that everyone is applying the same standards to whatever research they happen to be doing.
With respect to Newton, consider the fact that Newton's primary contribution was the Calculus — a mathematical system for modeling the movement of bodies with mass — and part of the paradigm he established is that physics should be math-based. But note that math has progressed since Newton's day, and people use Newton's math and methods to research things Newton never did. Think about the entire field of thermodynamics, which is based on Newton's principles, but came into existence a hundred years or so after Newton's death.
Of course, this outward expansion of research eventually leads to the discover of anomalies in the original paradigm, which can lead to new paradigms. Einstein used sophisticate maths to expose and quantify flaws in Newton's theories under the effects of gravity; quantum physics took mathematical analysis in entirely new directions from Newton's clockwork physics. Such people are still within the original paradigm — they are 'doing physics' in the way that Newton 'did physics' — but they have expanded beyond that work to create new exemplars.