Final answer:
After formulating a hypothesis, the next step for a scientist is to conduct an experiment to test the hypothesis, determine its validity, and decide whether it needs modification or further testing.
Step-by-step explanation:
After a scientist develops a new idea based on observations of nature, the next step in the scientific method is to conduct an experiment to test their hypothesis. This is because an experiment allows the scientist to evaluate the validity of the hypothesis by providing measurable evidence for or against it. If the results support the hypothesis, they can consider it valid and proceed to the next step. If not, they may need to modify the hypothesis and test it again or even discard it if it's proven completely wrong. This crucial process of experimentation helps refine scientific understanding and eventually leads to the development of scientific theories or laws.