What to do:
- You could present a fact (a verifiable fact) that contradicts it (this, of course, means that you have to be sure you understand the theory that you are trying to contradict).
- Or you could put forward your own testable theory - but it will have to be at least as good as the existing theory at explaining all the available evidence.
What not to do:
- Make an argument from personal incredulity.
- Argue that the theory fails because there are things that scientists don't know yet - no scientist would claim otherwise.
- Say something's wrong when all the evidence suggests that it's correct.
- Argue that the theory is wrong because some scientists have done something fraudulent in obtaining their results.
- Make ad hominem attacks on the scientists, rather than engaging with their ideas.
- Present as evidence the opinions of people who don't work in the field in question.
- Object to the theory because you don't like its consequences.
- Claim that the scientist later renounced his theory (a claim commonly - & incorrectly - made about Darwin). Even if true, it doesn't invalidate the theory.
In other words - an excellent checklist if you are weighing up a the arguments about a particular scientific theory :-) Again, my thanks to the Curmudgeon.