How can a scientist prove that smoking can cause lung cancer?
Technically, science doesn’t prove things, it isn’t math. What it does is use experiments and observations to formulate and then test theories. But there’s no test that can prove that a theory is entirely correct. The best we can hope to do is see if the theory fits known facts and makes valid predictions. So, in this case, you’re a surgeon and you notice that most of your lung cancer patients smoke cigarettes. That’s what happened, back in the 1930’s. So you develop a theory: smoking causes lung cancer. How do you find evidence for it? What you do is you study people who smoke and people who don’t and see if one group gets more cancer. You study people who died of cancer and see if more of them smoked than belonged to the regular population. And you try to weed out other factors that might be causing it, for example, age and whether they’ve been exposed to pollution. When all that was done, there was a pretty compelling connection — smokers were much, much more likely to develop lung
