Grandboy (playing a video game): Look, my guy is in a lighthouse.

Me: That’s pretty cool, having a house you can pick up.

Grandboy: Huh?

Me: Because your house is very light. It’s a LIGHT house.

Grandboy: O no grandpa, it’s a house that MAKES light. It’s too heavy to carry. Except for the Hulk, he can pick it up. He can pick up ANYthing.

Me: I bet he can’t pick up GRAVITY

Grandboy: O YES HE CAN. He can pick up THE UNIVERSE

Me: Well, if he’s picking up the universe, what’s he standing on? He has to stand on SOMETHING to pick up everything else.

Grandboy: He just CAN, alright, gwumpa?

Me: Ok fair nuff.

Me (waiting a few mins): So how heavy is light? Can the Hulk pick that up?

Grandboy: Yes he- o wait, no cuz it doesn’t WEIGH anything. You can’t carry it around.

Me (waiting a few mins more): So if light doesn’t weigh anything, how fast can it go? It has to travel because if you’re in a dark room and switch on the light, it moves from the light bulb to your eyes.

Grandboy: Hm maybe BILLIONS and BILLIONS. It’s the fastest thing in the WORLD. That’s why the Flash has LIGHTNING on his costume.

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Ok that’s general relativity framed up, on to quantum mechanics… just have to make sure he’s learning real science and not comic book physics 😛