how do scientists confirm things like the universe is expanding rather than contracting?

Question

how do scientists confirm things like the universe is expanding rather than contracting?

In: Physics

Answer 1

The gist of it is that they first make observations, and form a hypothesis.
Based on more observations they develop a theory that fits with the observations and (crucially) that can be used to predict development of a phenomenon/value/attribute.

If the theories explanation and prediction works, it’s accepted until someone makes different theory that works *better*.