Galileo GalileiTelescope. Tea. Trouble with the Church.

The sticker says Telescope. Tea. Trouble with the Church. The physics is in the gap between the telescope and the trouble.

In 1610 Galileo turned an improved telescope on Jupiter and found four points of light that travelled with it, night after night: moons circling something other than the Earth. He published them that year in The Sidereal Messenger. It did not prove that the Earth moves, but it removed the argument that everything must circle us. In 1633 the Church tried him for defending the Sun-centred system in his Dialogue and sentenced him to imprisonment, which he served under house arrest.

He kept working. His last great book, Two New Sciences, published in 1638, set out the mathematics of motion. Galileo slowed falling down by rolling balls along gentle ramps, where the motion was slow enough to time. His result is the first formula on this page: distance from rest grows as the square of the time. The second line is the same law in a form you can check with a ruler. In equal successive intervals, a falling body covers distances in the ratio 1 : 3 : 5 : 7, the odd numbers. Add them up and you get 1, 4, 9, 16, the squares. The odd numbers are what make it a square.

The same book argues that without air, heavy and light bodies would fall together. At the end of the last Apollo 15 moonwalk in 1971, commander David Scott dropped a 1.32-kilogram hammer and a falcon feather side by side on the Moon. They hit the ground together.

Galileo was not the first to look up, nor the first to doubt Aristotle. He rolled the balls, timed them, and wrote the numbers down.

Telescope, tea, trouble. The odd numbers came first.