It's very difficult, if not impossible, to 'prove' a negative but it's very straightforward to demonstrate that any given hypothesis (e.g. All railway modellers are autistic) is false. It's known as the 'black swan argument', in that it's easier to disprove the assertion that all swans are white, as all you need to do is to find a single black swan to disprove ('falsify) the assertion / hypothesis, rather than it is to check all the swans in the world to prove that they are all white. I wouldn't advise the latter course of action anyway, as they're horrible creatures (says someone who was attacked by a swan in 1967 when it bit me AND stole my ice cream cornet).