Peter Griffin here to explain the joke. Einstein was a smart guy and people will typically post quotes of the smart things he has said. However, this meme is quoting Einstein saying "Hi" to someone, which is a very simple and routine thing people do. The reader believes they will read an enlightening Einstein quote only to have their expectations subverted when they instead read a routine human interaction. Hehehehehe

He's replying h to the I power, at least I'm pretty sure that's the joke, sounds like a (admittedly bad) physics joke.

hi

free your mind