Let's say I don't believe the world is round. How can one prove the world is round to me?
Buy a ticket to Paris. Say you arrive at Charles de Gaulle airport. Take the RER B to Gare du Nord. At Gare du Nord, switch from the RER to the metro and take line 4, direction Mairie de Montrouge. Get off at the station Réaumur-Sébastopol. You’ll now be on Boulevard Sébastopol, take a left (or a right, depending on where you exit) to Rue Réaumur and walk for about 2 mins, past rue Saint-Martin, and you’ll finally see a church to your left, after which there’s a gate…
And… congratulations!! You’ve just arrived at the Musée des Arts et Métiers . Go inside (don’t be afraid now), go to accueil, and buy yourself a ticket (8 euros). Ask the receptionist to tell you where the Foucault’s pendulum is - it’s not the original one, that one is inside the Pantheón, but this way you’ll get the chance to visit the rest of the museum, which is great!
Now, how does this help? Because this pendulum was designed and built by Léon Foucault in 1851 precisely as an easy-to-build proof of Earth’s rotation along its axis!
It’s a basic concept - the pendulum is long enough to observe the Earth’s rotation along its axis, and the Coriolis effect. So go there, sit, and observe the pendulum as it swings back and forth. After a few minutes you will notice that the swing of the pendulum has rotated clockwise!!!! (yep! Notice the marks on the floor around it!). If you wait long enough, and if the security guards allow you to do it, stay there for a bit longer than one day (around 1 day and 7 hours, as Paris is at a latitude of about 49 degrees north of the equator (see below), and you’ll see the pendulum undergo a full rotation (360 degrees). While you’re waiting, make sure to read the above links, and try to understand what is at stake.. Was this enough??
Ok, ok, so maybe you’re still sceptical. Everything is rigged and it’s all a conspiracy… ok then, do this - go back to your hotel, and get some well-deserved sleep. Before you fall asleep though, make sure you book a flight to Oslo, Norway. From there contact this company. They will take you to the North pole. On the North pole you will need to reproduce the same experiment as the one you’ve just seen in Paris, so warn the organizers that you need to do just that. It won’t be easy of course, but it’s not impossible either! You want your proof so you have to work a bit to have it, right? So, mount your experiment, and after you do so, observe the pendulum again rotating clockwise on and on about its axis. Measure the time it takes for it to undergo a full rotation, and now, surprise!! … you will observe that it rotates 360 degrees in just 1 day, rather than 1 day and 7 hours as the one in Paris! How odd!!!
But don’t lose your stamina because we are not done yet. Get a good night sleep again, but before that remember to book yet another flight, this time to São Tomé and Principe, an archipelago near the Equator.
Arrive in São Tomé, and ask someone to take you to where the Equator line goes through. Again find a way to reproduce Foucault’s experiment. this will probably prove to be the most difficult part of this whole experiment, but hey, you’re the one asking for proof!! Now after you finish installing your Foucault’s pendulum in São Tomé, observe the pendulum again. This time, the pendulum will not rotate along its swinging axis at all!!!! WTF!!!!
How is this possible??????? What have we observed here?