Avogadro's hypothesis has proved significant till the present day.

Hypothesis : a supposition or proposed explanation made on the basis of limited evidence as a starting point for further investigation.
Fact : information used as evidence or as part of a report or news article.
Theory : a supposition or a system of ideas intended to explain something, especially one based on general principles independent of the thing to be explained.
Conclusion : the end or finish of an event, process, or text.
Experiment : a scientific procedure undertaken to make a discovery, test a hypothesis, or demonstrate a known fact.

Antonym of Hypothesis is Fact