It is seldom - perhaps never - possible to reach an absolute certitude when verifying a hypothesis. This is the case especially when the hypothesis is intended to hold true anywhere, i.e. also for the cases that are similar to those that have been examined. Therefore most modern researchers accept in practice the idea that when speaking of 'truth' of a hypothesis they actually mean verisimilitude or credibility. This distinction, nevertheless, has no decisive consequences in practice: you can use 'credible' findings exactly in the same way as 'true' findings.
CORRECTION: Especially when it comes to scientific findings about health and medicine, it can sometimes seem as though scientists are always changing their minds. One month the newspaper warns you away from chocolate's saturated fat and sugar; the next month, chocolate companies are bragging about chocolate's antioxidants and lack of trans-fats. There are several reasons for such apparent reversals. First, press coverage tends to draw particular attention to disagreements or ideas that conflict with past views. Second, ideas at the cutting edge of research (e.g., regarding new medical studies) may change rapidly as scientists test out many different possible explanations trying to figure out which are the most accurate. This is a normal and healthy part of the process of science. While it's true that all scientific ideas are subject to change if warranted by the evidence, many scientific ideas (e.g., evolutionary theory, foundational ideas in chemistry) are supported by many lines of evidence, are extremely reliable, and are unlikely to change. To learn more about provisionality in science and its portrayal by the media, visit a section from our .
If you choose to use research hypotheses, whether instead of research questions or in addition to them, these should be written differently to research questions. However, if you are using quantitative research questions, we have articles that can help you learn about the different and .