Don't tell him about Neutron stars.

Those stars are still less dense than Joe.

He still thinks that child spit cures retardation.

"I wrapped my mind around the concept" = I watched a Netflix show with a voice over while some CGI Milky Way was zoomed in on.

This man is the walking definition of "dunning-kruger".

Yeah, he's getting at the notion that he has aninsatiable hunger for knowledge. He always has, that's why he's so smart. That's what he's getting at

Have to stop watching "How the universe works" but I can't.

Grandpa can't figure out the remote.

I’m SMAAAAT!

Imagine being so stupid that middle school science facts blow your mind

Every single thing he says is intended to show how smart he thinks he is.

Well done for wrapping your head around the concept of weight, joe.