Forty people pedaling furiously toward nowhere, and not one of them is going anywhere. This delights me more than I can properly convey. Each rider is converting the chemical energy stored in their morning oatmeal, glucose bonds forged originally by sunlight in a leaf, into the mechanical work of spinning a heavy flywheel, which a felt brake pad then converts, through friction, almost entirely into heat.
That is the whole machine. You eat a sandwich descended from starlight, and the end product is a slightly warmer room.
Watch the flywheel itself. It is a solid steel disc, and to your hand it feels immovable, but it is nearly all empty space. If you scaled a single iron atom to the size of a cathedral, its nucleus would be a marble on the altar and the rest would be echoing air.
The disc holds its shape only because electromagnetic forces between those sparse nuclei refuse, absolutely, to let their electron clouds overlap. Every rider is straining against a wall of pure electrical refusal, dressed up as weight.
And the heat. All that human effort, the sweat and the shouting and the raised heart rates, obeys the same law as a cooling star: it flows one way only, from ordered motion to disordered warmth, and it never flows back. The room fills with the faint infrared glow of forty bodies running slightly above ambient, radiating away the last of that captured sunlight into the ventilation ducts.
They think they are burning calories. What they are actually doing is participating, with their whole flushed and determined bodies, in the same slow slide toward disorder that is running down every star in the sky.
A little louder, and set to music.