Well, here I go again. Another babbling with a silly question in title. It’s just… the ‘silly’ questions tend to be the smartest… but that’s another story. Down, below, beneath the floor, underground, call it as you like it – anyone knows how to go down the stairs or dig a hole in the ground. By the way, the word below comes from ‘be + low’. It would be utterly stupid to ask:
Heniek: How does everybody know where down is?
Zenek: Come on, it’s where the stuff falls! You can sense it!!!
Heniek: But… why do they fall? And what do we sense it with, noses?
Alright, now you know it’s going to be about gravity. Elementary school knowledge, boring. Or is it?
Gravity explains it all
It’s true that the theory of gravitational interaction explains a myriad of phenomena from our lives: a glass falling on the floor, spitting into your neighbor’s window, flushing pee in a toilet. And even Earth circling the Sun! Centuries ago, barely anyone thought about such stuff. For example, Aristotle has postulated an essentially simple matter in his convoluted arguments: objects tend to travel to their natural locations, the heavier ones lower, the lighter ones higher. That’s cool, but what’s the reason of falling down: weight or altitude?
After centuries of thinking, measuring and calculating (mostly of how planets move in the Solar System) by Newton and his pals, the law of universal gravitation was discovered.
You know what’s the most extraordinary? Not the fact that an apple fell on someone’s head. Not that a neat equation was formulated. Not the discovery of the gravitational constant. The most ingenious part was the unification of planetary movements and falling of objects into one phenomenon. When you realize that, a thought pops up itself: if the celestial bodies are governed by the same laws as apples, then maybe they aren’t driven by magic or God’s power. Perhaps they can be studied, known and familiar like apples. And another tiny detail that makes your head smoke:
Universality of gravity
Exactly. If celestial bodies attract each other like the Earth attracts the apple, then… the apple attracts the Earth as well. So, what falls down on what? That’s a matter of our human perception, not physics. The Earth and the apple move towards each other. It’s just the apple’s movement is clearly visible, while Earth’s movement is immeasurable (about a trillion trillion times smaller). But that’s not everything.
Universality means that every object attracts every other object… everywhere. The Sun attracts the Earth, Mercury, Jupiter, my socks 🧦. This brings some problems in calculations: to predict movements of celestial bodies, you need to include the gravity of the Sun, Earth and of the socks 🧦.
Alright, kidding 😉. But problems with calculations is another subject.
Is ‘down’ just a perception, too?
Sure is, just an impression! Inside the human ear, there is the vestibular system (very strangely shaped), which reacts to acceleration of the head. That includes the gravitational acceleration, so this is what ‘tells’ you which way is down! But it’s an organ, it can be defective like any other: after alcohol, with some diseases or on a hardcore merry-go-round. And on a space station, it has no purpose. Direction down is relative! In weightlessness, it’s even meaningless.
But what are such deliberations for?
Good question! There are several purposes:
- To realize that very distant things could not only have a relation, but even be one. Like gravity, describing of which has led to massive progress in understanding of the world.
- To realize that some obvious things aren’t obvious at all. Like the sensation ‘down’, which is the result of gravitational pull affecting a small organ in one’s ear.
- To realize that sometimes (just sometimes!) silly questions and absurd deliberations can bring incredible inspiration. For example, to Aristotle, Heniek and Zenek.
Farewell!