Let’s imagine another thought experiment. Let’s say, just for the sake of argument, that we had a time machine, and we’re about to go back 300 years into the past. We’re allowed to take a single scientific instrument with us, an experiment that we could use to prove beyond a shadow of a doubt something profound, something fundamental about the nature of our Earth or our place in the cosmos — something that people just refused to believe back in the 1500s.
What item would you take back with you?
Well, the scientific experiment that I would take back in time would be Miley Cyrus on her wrecking ball… I’d bundle her into the back of my DeLorean and drive back to the 1500s. There, I’d find a nice big cathedral, and hang Miley and her wrecking ball from the tall ceiling, and then give her a good push.
If you watch Miley swing back and forth on her wrecking ball (sat nice and comfortably like she seems to be in the picture here…) over the course of a day, you’ll notice something very strange happen, something that doesn’t immediately make any sense. Because Miley won’t keep swinging back and forth in the same direction, but she’ll seem to slowly twist around across the floor. Now, there’s no wind blowing inside this cathedral to deflect her, so the only conclusion you can come to is that the entire planet Earth itself is turning beneath Miley as she swings. You can use Miley Cyrus to demonstrate that the Earth isn’t flat, but that it’s a huge ball of rock and that it turns on it’s own axis. The reason the Sun seems to move across the sky (and the nighttime stars wheel around the heavens) isn’t because there’s some god on a blazing chariot dragging it around, but because the entire Earth is turning.
This experiment is known as Foucault’s Pendulum, and is covered briefly in Chapter 12 of The Knowledge. It’s a classic demonstration from the 1700s, and you’ll also notice that the magnitude of this effect – how quickly the pendulum seems to rotate around – depends on how close to the north or south pole you are. So you can use Miley Cyrus to demonstrate not only that the Earth is constantly turning on its axis, but even what your latitude on the Earth is.
And even better than that, if Miley happened to be wearing a wrist watch as you bundled her into your DeLorean, you could use just that to demonstrate beyond a shadow of a doubt that it is the Earth that orbits the Sun, and not visa versa. You can prove the ‘heliocentric solar system’, and the truth that the Earth isn’t in fact at the centre of everything, using nothing more than a simple clock.
All you need to do is watch when any particular star rises or sets below the horizon (or some other static landmark) each night, and note down the time from Miley’s clock. You’ll notice that this happens just under 4 minutes earlier each night. If the only motion the Earth experienced is its own spin then this wouldn’t happen. In fact, four minutes is almost exactly 24 hours (the length of one day) divided by 365 days (the number of days in a year). What’s happening, is that between each night the Earth has swept along in its orbit around the sun by one three-hundred-and-sixty-fifth, and so the world doesn’t need to have rotated completely to bring the same star back into view. Thus, any star seems to rise (or set) four minutes earlier each night.
Proving that the Earth isn’t the centre of the universe is merely a matter of having a good enough clock. Imagine all the trouble and stress — and threats of being burned at the stake — that could have been spared if only Copernicus and Galileo had had Miley Cyrus back in the 1500s…
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I will be doing a Reddit Ask Me Anything (AMA) session this Friday, 2nd May, starting at 4pm UK time (11am Eastern; 10am Central; 9am Mountain; 8am Pacific) and running through that day. Here’s the