Final answer:
Democritus, the Greek philosopher who never tested his theory of atomos, wasn't believed because Greek philosophers preferred thought and logic over experimental proof. John Dalton later validated the concept with experiments in the 19th century.
Step-by-step explanation:
The scientist who is known for not testing or proving his ideas, which led to them not being believed during ancient times, was a Greek philosopher named Democritus. He had proposed the theory of atomos, which is the concept that everything is composed of small, indivisible particles. However, his ideas were dismissed by other Greek philosophers who were known for their approach of "all thought and no action," relying solely on reason and logic without experimental verification.
It wasn't until much later, in the 19th century, that John Dalton, using experiments to test hypotheses, managed to present a modern atomic theory that was based on Democritus' ancient ideas. This illustrates how the scientific method and the need for empirical evidence have become integral to advancing knowledge, differing significantly from the ancient Greeks' practices. Unlike Dalton's experimental approach, the reluctance or inability to experimentally test theories meant that many Greek philosophers' ideas, like those of Democritus, remained unaccepted until much later.