The null hypothesis, H0 is a commonly accepted hypothesis; it is the opposite of the alternate hypothesis. Researchers work to reject, nullify or disprove the null hypothesis. Researchers come up with an alternate hypothesis, one that they think explains a phenomenon, and then work to nullify the null hypothesis.
Why is it Called the Null Hypothesis?
The word “null” in this context means that it’s a commonly accepted hypothesis that researchers work to nullify. It doesn’t mean that the hypothesis is null itself! (Perhaps the term should be called the “nullifiable hypothesis” as that might cause less confusion).
Why Do I need to Test the Null Hypothesis? Why not just prove an alternate one?
Science uses a battery of deductive and inductive processes to prove or disprove theories, making sure than any new hypothesis has no flaws. Including both a null hypothesis and an alternate hypothesis in your research is one safeguard to ensure your research isn’t flawed. Not including the null hypothesis in your research is considered very bad practice by those in the scientific community. If you set out to prove an alternate hypothesis without considering the null hypothesis, you are likely setting yourself up for failure. At a minimum, your experiment will likely be invalidated and not taken seriously.
Example of the Null Hypothesis
Not so long ago, people believed that the world was flat.
Null hypothesis, H0: The world is flat.
Alternate hypothesis: The world is round.
Several scientists, including Copernicus, set out to disprove the null hypothesis, eventually leading to the rejection of the null hypothesis and the acceptance of the alternate (well, most people accepted it — the ones that didn’t created the Flat Earth Society!). What would have happened if Copernicus had not disproved the null hypothesis and merely proved the alternate? No one would have listened to him — in order to change people’s thinking, he first had to prove that their thinking was wrong.