or vibrations in a crystal lattice, okay? in this particular case, the clock is regularly spaced flashes of light and one can keep track of time by counting up the flashes of light. so far so good? let's see what happens if we apply this to space travel. here's the earth, our cradle, gang. that's our cradle, the cradle of humankind. what do we do with cradles, by the way, even if they're comfortable? - we outgrow. - we outgrow them, that's right. and we see that starting to happen now, don't we? the spaceship's going out. we're talking about space platforms, okay? anyway, this is our cradle right here and here comes our rocket ship, same one, streaming by. and we're gonna say at this point, boom. both times are 12:00 noon. 12:00 on the ship, 12:00 on the earth and the ship continues. now, what the ship is gonna do? it's gonna take a one-hour trip out and it's gonna turn around very quickly. so quickly that the time is negligible in comparison to the hour trip. so ship is going out, turn around and come back. it's gonna take o