A very famous scientist explains a recently observed natural phenomenon with a new theory. Should the new theory be considered valid?

No

Explanation:

A theory is an adequately research explanation of observation that is in accordance with modern scientific methods. The theory should have undisputable empirical supports in form of scientific experiment which has rigorously and comprehensively proven the theory using scientific method and other scientists should also have similar observations when the theory is tested. As such the famous scientists phenomenon needs to be subjected to serious scientific testing before it can be established as theory.