The amazing story of the void: from ‘horror vacui’ to quantum physics

Aristotle said that nature abhors a vacuum, the famous “horror vacui,” and for centuries, no one dared to contradict him: it was believed that if a void appeared, matter would immediately fill it. But if you take a deep breath today, you are using a vacuum to survive: your lungs take advantage of the fact that air, although invisible, is full of molecules moving around. Everyone thinks that a vacuum is the opposite of matter, an absolute nothingness. The surprising thing is that, the more physics advances, the more we discover that the vacuum is full of things—and that it is one of the keys to understanding the universe. Four centuries ago, Galileo encountered a limit: using suction pumps, water would not rise more than 10 meters in wells. Why? His student Torricelli devised an experiment using a mercury tube: when the tube was turned upside down, the mercury would sink, leaving a transparent space at the top—the famous “Torricelli vacuum.” But that gap was not caused by suction; it was caused by the weight of the air: the atmosphere was pressing from the outside and supporting the column. Thus, the barometer was born, along with the certainty that air has weight. Pascal confirmed this in 1648 when his brother-in-law took the barometer up to Puy de Dôme and found that the higher the altitude, the lower the pressure: the atmosphere is finite, not infinite. Then came Otto von Guericke, who in 1654 took two metal hemispheres, removed the air, and had two teams of horses pull in opposite directions. Even so, they could not separate the hemispheres, because the vacuum inside caused the atmospheric pressure to keep them stuck together. Boyle and Hooke refined the vacuum pumps: Boyle rang bells, lit candles, and placed animals in airless containers. The bell did not ring, the candle went out, and the mice did not breathe. The vacuum ceased to be merely a philosophical idea and became a tangible reality – it even inspired paintings like Joseph Wright of Derby's An Experiment with a Bird in the Air Pump. Later, the vacuum became essential to science: without vacuum tubes, Röntgen would not have discovered X-rays in 1895, because electrons only pass through these tubes if the air has been almost completely removed. But the real breakthrough came with quantum physics. In the classical view, a vacuum means the absence of matter. In quantum field theory, on the other hand, a vacuum is the lowest energy state of the fundamental fields, and yet it is teeming with activity: quantum fluctuations, pairs of virtual particles that appear and disappear in the blink of an eye. You can't see them, but you can see their effects. The prime example is the Casimir effect, predicted in 1948 and measured in 1997. If you place two metal plates almost touching each other in a vacuum, the quantum fluctuations between them are less than outside the vacuum. The result: a mysterious pressure pushes the plates apart, as if the vacuum were exerting a force. It's like a violin string: depending on how you hold it, only certain notes vibrate. Thus, the quantum vacuum has real physical properties. Today, the vacuum lies at the heart of cutting-edge physics: the Higgs field, which gives mass to particles; the cosmological constant, which drives the accelerated expansion of the universe; and quantum electrodynamics, one of the most precise theories in history. The irony is that Aristotle was wrong about the details, but right about the big picture: the void was never simply nothing, but rather a hidden protagonist of reality. Now, consider this: The next time you see a seemingly empty space, remember that it may be more filled with physics than anything visible. If, after listening to this, you feel that your idea of the vacuum has changed, you can mark it in Lara Notes with I'm In — it's not a “like”; it's a way of saying: This perspective is now yours. And if you end up telling someone the story of the Magdeburg hemispheres or the Casimir effect, you can record it with Shared Offline: that way, the conversation that makes science come to life is preserved. This content comes from The Conversation, and with this Note, you've saved yourself nearly four minutes of reading.