We cannot see it but we need it to live – and to fly through the sky. In praise of air.
When you’re flying 9000 meters above the ground and look out of the window, what do you see? Most people would say: clouds, sky and the earth far below. They wouldn’t say: air. We know of the existence of this invisible mixture of gases, but we seldom think about it. We cannot grab a hold of air and usually cannot smell it. It is beyond our senses’ perception.
The fact that we associate air with absence, with something that isn’t there, is reflected in our speech. If someone disappears suddenly, we say they have vanished into thin air. A person who talks nonsense is full of hot air. To make unrealistic plans is to build castles in the air. And baseless theories can be said to be plucked out of the air. It’s as if our mind wanted to deny the existence of this omnipresent element. But what would we be without it? We need it to breathe, we need it to live. And naturally, we need it to fly. Without air, no plane could take off and no bird could glide through the sky. The time has come to pay tribute to the ethereal element flowing past our window.
For a long time, humans didn’t understand the concept of air. What was it that we breathed and were able to forcefully expel? Nothingness? The breath of God? The Greek natural philosopher Anaximander was one of the first to attempt an explanation. Around 600 BCE, he is said to have described what surrounds the earth and what humans feel when the slightest breeze blows like this: “Wind is a flowing of air.” What sounds self-evident to us was a revelation back then.
Observe the fish in the water and you will understand the birds in the air
In the third century BCE, Philo of Byzantium discovered that air was a substance, but it wasn’t until roughly 1800 years later that Galileo Galilei succeeded in proving that air actually had weight. This was a bold assertion in an age when people had a hard time believing earthly explanations for things they couldn’t see. In the end, it was the quicksilver experiments conducted by Italian physicist Evangelista Torricelli that convinced them. Torricelli filled quicksilver into small glass tubes and was amazed to observe its level rise and fall according to the weather. This resulted in the invention of the barometer, a device capable of measuring the pressure applied to the earth by enormous masses of air and the key to understanding weather. From then on, it was accepted that air was not nothing but rather something quite concrete.
In fact, our atmosphere, which is roughly 100 kilometers thick, does weigh heavily on the planet. One cubic meter of air weighs just under 1.3 kilograms. Applied to the pillar of air directly above our heads, that’s the equivalent of roughly ten tons of air per square meter of ground at sea level – and a weight of around 17 tons bearing down on each of us. Yet we feel none of it, because our bodies naturally exert the same amount of pressure to create an equilibrium.
Today, our air is made up of 78 percent nitrogen, 21 percent oxygen, 0.9 percent argon and other noble gases and 0.04 percent carbon dioxide, not to mention dust, steam, sulfur and nitrogen compounds, exhaust fumes, and plant and animal microorganisms. It’s quite a colorful mixture. People like pilots, who concern themselves with air, have a very clear picture of what it is and does. And the experts, like the inventor of the barometer, Torricelli, no longer talk about humans living on the surface of the earth but rather on the floor of an ocean of air.
This ocean of air is very alive, continually moving and flowing, forming eddies and waves and vortices. Sometimes it’s thick, sometimes thin, sometimes warm, sometimes cool, but it is never still. Even on a perfect, “windless” summer’s day, billions of molecules dance furiously around us. Storms rage in the air and waves crash in this invisible sea. Everything that moves in the air leaves a trail behind, interrupting the flow like a post in a swiftly moving river.
Airplanes cross this invisible sea, plow through this intangible ocean of air as they navigate its heights and depths. En route, they encounter the most curious laws. They create c, their own wake of vortices, so to speak. In fact, air sometimes moves so rapidly that pilots find themselves navigating its currents like a ship’s captain navigates the sea. The narrow, fast-flowing currents of air known as “jet streams” sometimes shoot across the sky at over 200 kilometers an hour. Pilots enter them to tap into their speed. There are actually two speeds in the sky: One is measured relative to the air and the other relative to the ground. A pilot flying at an air speed of 600 kilometers an hour might be moving at a ground speed of close to 800 kilometers per hour. The air can also hinder a plane’s progress, however, which explains why flying out in one direction can take longer than flying home in the other.
Ultimately, it is the weight of the air that makes it possible for an airplane to take off. Its wings cut through the air and its molecules flow around the curve of the wings, faster along the top than along the bottom. This creates lower pressure on the top and higher pressure on the bottom so that the wings are lifted into the air. The Swiss physicist Daniel Bernoulli formulated the basic principle of flight when he described this effect in the 18th century. We can observe this phenomenon elsewhere, too: When you stick your head out of the window of a moving car, the wind doesn’t blow your hair into the car but rather pulls it out. Strong winds don’t make roofs collapse into houses, they lift them off.
In the end, there is also something philosophical about the air. It silently challenges us to investigate the reality behind what’s in the world, to discover the things we cannot see. This makes the air as miraculous as an invisible sea. The universal thinker and inventor Leonardo da Vinci already saw the parallels a good 500 years ago: “Observe the swimming of fish in the water and you will understand the flight of birds in the air.”