There's the dichotomy of an irresistible force meeting an immovable object - only one of these is possible. Either there can be an undefeatable AI detector, or

There's the dichotomy of an irresistible force meeting an immovable object - only one of these is possible. Either there can be an undefeatable AI detector, or an undetectable AI writer, both can't exist in the same universe. And my assumption is that with sufficient advances there could be a fully human-equivalent AI that is not distinguishable from a human in any way, so in that sense being able to detect it will actually never work.