The null hypothesis (H0) is a statistical and scientific tool to test a hypothesis. It usually refers to a default state. Think of it as the "killjoy hypothesis."
- Blood pressure lowering drug X: that drug X maintains blood pressure.
In a hypothesis test, the null hypothesis can be rejected or can fail to be rejected; it cannot be proven or validated.
This can be applied more broadly, particularly when dealing with pseudoscience:
- Homeopathy: that water prepared by dilution and succussion is indistinguishable in its medical effects from water that has not.
- Nanobots: that matter at nanoscale does not behave as hypothesised by Drexler.
- Cryonics: that information in the brain is not sufficiently preserved by the freezing process.
The burden of proof is on the person advocating the idea to present convincing evidence which would cause one to reject the null hypothesis. Were that to happen the burden of proof would fall to the person against the idea who would have to refute or explain the evidence.
The following cases are examples where sufficient evidence has been presented and the null hypothesis can be rejected.
- Climate change: that human influence has not changed Earth's climate.
- Evolution: that species are not changed by natural selection to fit an ecological niche.
Given that the null hypothesis has been rejected it now falls to those who would wish to deny the evidence for global warming or evolution to present their counterarguments. The burden of proof is on them.