Oh! This actually is something that falls into my area of expertise. You weren't getting me mixed up with a Green Lantern! I have to tell Ted!
That's not really an easy question to answer. The fact that they're from an alternate world already means that something in their timeline is different from our own. There might be enough of a difference that it might not matter too much if you tell them or not.
Who were you thinking about talking to and what did you want to tell them?