> were they doing enough experiments that they'd have eventually said it couldn't exist if they never found it for some amount of time? No, that's called "prov

> were they doing enough experiments that they'd have eventually said it couldn't exist if they never found it for some amount of time? No, that's called "proving a negative" -- in most cases it's an impossible evidentiary burden. For example, no one will ever be able to say that Bigfoot doesn't exist for lack of evidence. This is why the null hypothesis is the default scientific precept -- that something without evidence is assumed not to exist (but by no means proven not to exist). http://en.wikipedia.org/wiki/Null_hypothesis http://en.wikipedia.org/wiki/Null_hypothesis