who can travel in the pond theory

S1 and S2 spoilers, no mention of anything in S3!

I've had a theory in mind since last season about who can travel in the pond. Elliot states that the people who can travel in the pond are the Landrys and anyone accompanying them, but I think it's simply the Landrys that can time travel; the definition of a Landry is just more broad than what Elliot thinks it is.

Fynn is a Landry, he's their family dog. That's why he can time travel. That brings up the question as to how Elliot can time travel though. I think he ends up marrying Kat, making him a Landry in the future. And since the pond has a different way of seeing time than all the people in the show, wouldn't it make sense that it views him as always being a Landry, even when he jumps in with Alice in 2024? He just couldn't time travel when he jumped in in the 90s because it wasn't time for him to do so yet.