Found myself writing this for a comment somewhere, here for posterity
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If you were psychic you’d see some event happening in the future.
Suppose that the future is determined by what the state of the world is now (time1).
A psychic sees an event in the future that follows naturally from time1.
If a psychic tells anyone their prediction, they change the state of the world, and (butterfly wings etc) introduce the possibility this event might not come to pass. Events would follow naturally from this state of the world where the prediction was made (time2).
If a psychic doesn’t tell anyone, then the event comes to pass, but no one will ever know the prediction took place.
Maybe a psychic could prevent the event from happening without admitting they were a psychic or that they knew anything about it – they could reset someone’s alarm to stop them going on an otherwise fatal car journey. But 1) we wouldn’t know how often this happens because the event would be prevented, and 2) this wouldn’t necessarily imply that nothing bad would ever happen because not all events are necessarily predicted, and not all psychics are necessarily able to act on their prediction.
It seems like if you were going to have knowledge about the future it would be in the form of either a future event, or a series of events leading to a future event. If you share this prediction, you introduce a new element and invalidate the prediction. Maybe the way the world actually works is that no matter what any agent does, ‘the world’ will continue towards some events. But if this were true then we’d probably have seen psychics more often.
The question is basically “if someone predicts accurately that you will die tomorrow under a piano on 5th avenue can you do anything to prevent this?”
Basically it doesn’t seem that implausible that if someone knew something was going to happen that he couldn’t say anything about it without preventing it, making his claim impossible to verify
