Galileo's Ship

Galileo adalah salah satu saintis yang secara terbuka mendukung teori heliosentris Copernicus; salah satu implikasi teori ini adalah bahwa bumi tidak diam, melainkan berotasi dan berevolusi. Di masa itu — bahkan sekarang, kalau kamu tanya anak SD; keraguan paling mendasar dari teori Copernicus adalah: jika benar bumi berputar, mana mungkin kita tidak merasakannya?

And this is his brilliant answer. Welcome to Galileo’s ship.

Shut yourself up with some friend in the main cabin below decks on some large ship, and have with you there some flies, butterflies, and other small flying animals. Have a large bowl of water with some fish in it; hang up a bottle that empties drop by drop into a wide vessel beneath it. With the ship standing still, observe carefully how the little animals fly with equal speed to all sides of the cabin. The fish swim indifferently in all directions; the drops fall into the vessel beneath; and, in throwing something to your friend, you need throw it no more strongly in one direction than another, the distances being equal; jumping with your feet together, you pass equal spaces in every direction. When you have observed all these things carefully (though doubtless when the ship is standing still everything must happen in this way), have the ship proceed with any speed you like, so long as the motion is uniform and not fluctuating this way and that. You will discover not the least change in all the effects named, nor could you tell from any of them whether the ship was moving or standing still.