The phrase “nature abhors a vacuum,” or horror vacui in Latin, suggests that empty spaces are unnatural and will quickly be filled. This idea originates from ancient Greek philosophy, particularly from the teachings of Aristotle. For centuries, this concept guided explanations for various natural phenomena, assuming nature actively prevents empty space.
The Ancient Idea
Aristotle, an ancient Greek philosopher, proposed horror vacui, asserting that a true vacuum, an absolutely empty space, could not exist. He reasoned that nature inherently seeks to fill any void, arguing that if a vacuum existed, motion within it would be limitless due to a lack of resistance. Believing infinite speed impossible, he concluded a vacuum must also be impossible. This idea, that denser material would immediately fill any void, was widely accepted for nearly two millennia, influencing scientific thought before experimental science.
Unveiling Atmospheric Pressure
The scientific understanding of empty space shifted in the 17th century with experiments demonstrating atmospheric pressure. In 1643, Italian scientist Evangelista Torricelli conducted a pivotal experiment. He filled a long glass tube, sealed at one end, with mercury and inverted it into a basin, observing the mercury column remained suspended at about 760 mm. Torricelli concluded that the weight of the air surrounding the basin exerted pressure on the mercury surface, supporting the column, rather than nature’s “abhorrence” of a vacuum. The space above the mercury, known as a Torricellian vacuum, was the first laboratory-created vacuum.
Building on Torricelli’s work, French physicist Blaise Pascal further confirmed atmospheric pressure. Pascal reasoned that if air had weight, atmospheric pressure should be lower at higher altitudes. In 1648, he had a barometer carried up the Puy de Dôme mountain. As it ascended, the mercury column progressively dropped, proving atmospheric pressure decreases with altitude. These discoveries provided a measurable, physical explanation for phenomena previously attributed to nature’s “fear of the void.”
Modern Understanding of Vacuum
In contemporary science, a vacuum is not an absolute void, but a space with significantly reduced pressure. A perfect vacuum, entirely devoid of matter, remains a theoretical ideal, practically impossible to achieve. Even outer space, often considered a vacuum, contains stray particles and radiation, making it an extremely high-quality partial vacuum.
Vacuums are created by removing gas molecules from an enclosed space using vacuum pumps. The degree of vacuum depends on the remaining gas molecules and resulting pressure, ranging from rough to ultra-high vacuums. Modern technology utilizes vacuum principles in devices like vacuum cleaners, thermos flasks for insulation, and in manufacturing electronics and pharmaceuticals. Quantum physics suggests that even seemingly empty space is not truly empty, experiencing continuous fluctuations where virtual particles briefly appear and disappear, reinforcing that a classical void does not exist.
Everyday Pressure Phenomena
Understanding atmospheric pressure explains many common phenomena once attributed to nature’s “abhorrence” of a vacuum. Drinking straws, for instance, operate not by “sucking” liquid up, but by reducing air pressure inside the straw. Higher atmospheric pressure on the liquid’s surface outside then pushes the liquid up. Similarly, siphons work due to elevation differences and the interplay of atmospheric pressure and gravity, causing liquid to flow from a higher to a lower reservoir.
Suction cups also rely on pressure differences to adhere to surfaces. When pressed onto a surface, air is expelled, creating a sealed space with lower pressure inside. Greater atmospheric pressure outside then presses it firmly against the surface, creating a strong adhesive force.