Bob walks into a bar holding a clock and a meter (yard) stick and runs back and forth past the bartender at close to the speed of light. This is as fast as he can run.
Alice, the bartender, says, “Your clock is slow and your meter stick is short, see, look”, and she holds up her own clock and meter stick.
Bob is running up and down the bar and says, “No, your clock is slow and your meter stick is short!”
That is special relativity.
They then jump into a car and Alice ties a blindfold around Bob’s eyes.
Alice steps on the gas, accelerating the car. Bob asks her, “Are we going uphill?” Alice answers, “Wouldn’t you like to know.”
That is general relativity.
Seriously.
