Late one evening, pixel Albert Einstein drops in on an old clockmaker friend to borrow a quiet corner for thinking. The slate floor of the workshop makes a perfect chalkboard, so he draws a big grid across it to picture space and time. Then something odd happens: a little wind-up alarm clock hops off the shelf and ticks along behind him, then another, then a third. His friend laughs and names the walk the Tick-Tock Trot.
Every stick of chalk he picks up lets him draw one more line on the grid, and one more clock joins the back of the queue, which ticks along a little faster each time. The chalk grid has no edges at all: walk off one side and he steps back in on the other, so the only thing that ends the walk is stepping on the tail of his own ticking line. Now and then a light bulb of a bright idea glows for a moment, worth a special note in the margin. How long can the line get before every clock rings at once?
