The null hypothesis is like the empty set: there's no claims inside it. The negation of a claim is another claim independent of the first. Suppose I show you a

The null hypothesis is like the empty set: there's no claims inside it. The negation of a claim is another claim independent of the first. Suppose I show you a jar containing a large number of coins and I claim the number of coins is even by just looking at the jar. Do you have evidence that I am correct? No! Just by looking at it I can't possibly know the exact number of coins. But this means that the logical negation of my claim is true ( the number of coins is odd?). Also no! Again, I can't know the exact number of coins by just looking at it. So although there are only two possibilities, I have no evidence at all. And this means the only claim I can make is the null hypothesis: I don't know. Absence of evidence is not, itself, an evidence of absence. In other words, if I don't have evidence that you committed a murder, it doesn't mean you're innocent. It means just that: I don't have evidence to convict you, and I must dismiss the case.