SteveN writes:
In science, however, it is usual to accept that absolutely proving the non-existence of something is not possible. To be honest, I'm actually not convinced that this is necessarily true.
It can be assumed so, and science will work fine with that assumption, but in an epistemological sense we can't know whether we are right to assume this.
My reasoning is, the statement "we can't absolutely prove the non-existence of something" is itself asserting that it has been absolutely proven that: 'absolute proof for the non-existence of something doesn't exist'. That statements effectively commits suicide when you think about it.
"Der Mensch kann was er will; er kann aber nicht wollen was er will." (Man can do what he wills but he cannot will what he wills.) - Arthur Schopenhauer