American Scientist

I remember Felix Baumgartner jumping from a high-altitude balloon 39 kilometers above the Earth’s surface. It was streamed live on the internet in 2012. Before he jumped, we saw footage of him in his capsule, on the edge of space, preparing to leap. Below, we could see the blue planet Earth in all its spherical magnificence. Baumgartner was wearing a spacesuit because his balloon had reached the stratosphere. At that height, there is very little of the Earth’s gas atmosphere and almost no oxygen. The temperature outside the capsule was –57 degrees Celsius. As I waited, watching the live video feed, I envied him being up there between heaven and Earth, in this place where the gas atmosphere of our planet ends and the mysterious sublime state of nothing stretches out into the universe.

The materiality of space has puzzled humans throughout the ages. What really is it? Surely space can’t actually be nothing? The ancients agreed. Aristotle declared that “nature abhors a vacuum.” The heavens were thought to be filled with a sacred material. The Greeks called it aether, the substance the gods breathed, the fifth element, separate from the four that made up the earthly realm: earth, air, fire, and water. It allowed light from the stars to propagate, and by medieval times it was also holding planets in their orbits. Even when Isaac Newton proposed gravity as a force in 1666, it relied on aether to propagate across the Solar System. But no one could actually find a trace of this material, and as science began to rely on it more, so finding it became more urgent. The story of the search for this material starts back on Earth—the same Earth that Felix Baumgartner hurtled toward at some 1,357 kilometers per hour as he jumped from his balloon on October 14, 2012, almost certainly not thinking that the technology protecting him from the vacuum of space was in any way linked to this ancient quest for aether.

Under Pressure

An Italian and a student of Galileo Galilei called Evangelista Torricelli was one of the first to make a breakthrough in the search for aether in 1641. His experiment was simple and elegant. He took a tube of mercury and turned it upside down in a bowl of mercury. Remarkably, such an experiment shows that mercury does not rush down to the bottom of the tube pulled by gravity, as you might expect. It falls a short distance and then stops. For a meter column of mercury, roughly 76 centimeters of it stay up the tube, defying gravity. But there is a gap at the top where 24 centimeters of mercury used to be but are not there anymore. Torricelli asked what is in the gap. It is not air, because no air could get in. So it is a vacuum, just like the vacuum of space, and presumably filled with aether. Could this invisible aether be responsible for the mysterious force holding up the mercury against the force of gravity?

The answer is no. Torricelli showed that there was a much simpler explanation. The air we breathe forms atmosphere on our planet, and despite being a gas, it has weight. It pushes down on us and everything it surrounds. It is this air pressure that pushes down on the bowl of mercury, pushing the mercury up the tube. At the same time, the column of mercury is pulled down by gravity. When those two forces are equal determines the height of the mercury. This balance is why the height of the column changes depending where you are on the Earth’s surface. At sea level, the height of the mercury column is 760 millimeters. If you go up a mountain, the column gets smaller. This change is because there is less air above you, less air pushing down on the surface of the mercury in the bowl, so less pressure pushing the mercury up against the force of gravity. If Baumgartner had done this experiment in his balloon 39 kilometers above sea level, he would have found that the tiny amount of atmosphere above him pushed so feebly that the height of the mercury column would have been 3 millimeters. So the vacuum doesn’t do anything; its role is not to push back. What Torricelli had done was to find a way to create a vacuum on Earth. It had lots of technological implications, some of which would end up being the creation of TVs, computers, and vacuum cleaners. But before that, a more immediate invention beckoned, a way to measure atmospheric pressure: the barometer.

The barometer turned out to be able to predict the weather—or at least some aspects of the weather. It could detect invisible changes in air pressure associated with different weather patterns, because they changed the height of the column of mercury in the glass tube. Those analyzing weather patterns realized that high pressure was often associated with clear skies and sunny weather, whereas low pressure (a small column of mercury) accurately preceded rain and storms. The phrase “the mercury is sinking’” started to become used by sailors. It meant that the height of the column of mercury in their barometers was decreasing, indicating a low-pressure weather system was approaching and potentially a storm. Now they didn’t have to pray to the wind gods or leave them offerings in order to know when was a good time to set sail. To this day, air pressure is still measured in millimeters of mercury, denoted mmHg, as a result of this invention 400 years ago.

The development of this weather-forecasting tool was an unexpected bonus of exploring nothingness, but scholars of the time still had the puzzle of vacuums. Surely a region of the glass barometer with absolutely nothing in it was impossible: It had to be filled with something, even if that something was not air. Light travelled through the space at the top of a barometer, just like it travelled through outer space. So, they argued, they both should be filled with aether. They considered it a fundamental element of the universe, a perfect substance, but one that could perhaps be chemically isolated.

The materiality of space has puzzled humans throughout the ages. What really is it? Surely space can’t actually be nothing?

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So the quest to isolate and distill aether began. It was led by the alchemists, who called it quintessence (the fifth element) and thought it could be used as a medicine to cure disease. Illness, at the time, was thought to be something that came from within a person, an imbalance of the four humors: black bile, yellow bile, blood, and phlegm. Quintessence, the perfect substance, it was argued, could balance these humors and thus cure a person of illness. Others came to believe that quintessence was the fabled philosopher’s stone that could turn base metals into gold. Once again it was a question of balance: Lead had an imperfect balance of the fundamental substances sulfur and mercury, and was thus a base metal that was soft and corroded easily. Quintessence could adjust the balance and so make this substance into perfect gold. Success in distilling quintessence would bring fame and wealth, but more importantly, complete their quest to become close to God by studying and understanding God’s creation. And so the search for quintessence became a holy quest.

Stuck Together

The person who made the next big breakthrough was not an alchemist, though, but the mayor of the German town of Magdeburg, Otto von Guericke. As a politician, he traveled across Europe, which meant he was exposed to new ideas and the big scientific problems of the day. A devout man, he got to hear that quintessence might be the substance that filled the vacuum at the top of a barometer. Not being an alchemist turned out to be an advantage, because he did not have preconceived ideas of the right way to obtain quintessence. While alchemists were using all sorts of methods of chemical distillation, von Guericke did something completely different: He decided to isolate nothingness mechanically.

To do so, he invented an air pump. It is a device we would recognize today as similar to a bicycle pump, except that the valves are reversed, so that each stroke of the cylinder removes air from whatever it is connected to, and then on the return stroke prevents the air from coming back. The mechanism is simple, but the execution is not. Whenever you remove air from a container, the air pressure outside the vessel creates a force driving air back into the container. This force gets bigger the more air you remove. Any leak in the valves or the fabric of the container destroys the vacuum. So to make it work requires precision engineering.

We take the accuracy and intricacy of screws, gaskets, and valves for granted today. In the 17th century, such precision engineering was just beginning: For instance, the mechanical clocks in city centers were only able to keep time to an accuracy of 10 minutes in a day. Nevertheless, through ingenuity, perseverance, and many failures, von Guericke succeeded in constructing an airtight pump. Despite this engineering success, he probably wouldn’t have been credited as being pivotal to the understanding of vacuums if he hadn’t also been a bit of a showman. He showed the power of his air pump with a demonstration that would blow the minds of everyone who saw it.

Von Guericke made two hemispheres of bronze that were machined so accurately that when they were placed together, they fitted to each other exactly. One had a small pipe incorporated to allow von Guericke’s vacuum pump to be fitted. Then he assembled the important people in the land, including the king of Prussia, to witness something incredible. He showed everyone the two hemispheres. They were just two pieces of not-very-interesting metal. Then he put them together to create a hollow sphere of metal. Next, he used his air pump to remove the air from this internal space and create a vacuum. Now there was nothing physical holding the hemispheres together: no bolts, no straps, no welding, no glue. Everyone could see that. Nothing. Then he assembled two teams of eight horses. The first team of horses was harnessed to one-half of the now-joined Magdeburg sphere (as it came to be called) and the second team to the other, the two teams facing in opposite directions. Presumably, the horses neighed and stamped their hooves, not knowing what was going on. Perhaps the wind dramatically ruffled their manes. Then von Guericke drove the two teams away from each other, trying to make them pull the two halves of the sphere apart. They pulled against suction, but they could not defeat it. A pump, and some precision engineering, had created a suction that could defy 16 horsepower. But it wasn’t a force from the vacuum inside. Just as with the barometer, atmospheric pressure was pushing the two hemispheres together, and, without air inside, nothing was pushing back.

Investigating Nothingness

Soon, engineers and instrument makers across Europe were building their own air pumps and using them to explore the anatomy and properties of vacuums. As with von Guericke’s demonstration, part of the magic was the public nature of the experiments. Famous scientists of the day such as Robert Boyle started using air pumps to evacuate glass vessels, so that anyone who cared to look could see what was going on inside. These demonstrations became public entertainment as well as pushing forward the science.

Does a bell ring in a vacuum? Answer, no: Sound waves need air as a medium to travel. Does a candle burn in a vacuum? Answer, no: But oxygen had not been discovered yet, so there was no good explanation. Can an insect fly in a vacuum? Answer, no: Wings need a gas to create lift. Can a snail survive in a vacuum? Answer, no: It dies. Can a mouse survive in a vacuum? Answer, no: It dies. Can a bird fly in a vacuum? Answer, no: It flutters and then dies in agony. What happens if you put a compass in a vacuum; does it still point north? Answer, yes: Magnetism is unaffected by a vacuum. Does electricity flow in a vacuum? Answer, yes: And light travels through it without a hitch too. Ah-ha, you’re thinking: A clue! And yes, you’re right, this result is exactly why the scientists of the day were so excited about these discoveries.

So it was that von Guericke’s air pump was crucial to build the evidence that although some things, such as sound, needed the medium of air to travel, others, such as light, magnetism, and electricity, did not. Perhaps they were special in some way, or perhaps they were connected to whatever there was in a vacuum that allowed them to travel, not just through a vacuum but across space and time. The potential role of quintessence was expanding.

In 1768, the spectacle of the popular and mysterious air pump experiments was captured in a painting by Joseph Wright of Derby in the United Kingdom. Called An Experiment on a Bird in the Air Pump, it now hangs in the National Gallery in London. There is wonder and sorrow in that painting. The central figure conducting the experiment is a man looking out toward the viewer with an impartial expression, as if to say, “This is how to understand the world.” Some of the onlookers are covering their eyes, distressed at the cruelty of experimenting on live animals. Others are staring intently at the demonstration, utterly fascinated by this insight into how the universe works. On the table is a small Magdeburg sphere, a reference to the origin of these pumps and the quest to understand air, vacuums, and quintessence.

Whenever you remove air from a container, the air pressure outside the vessel creates a force driving air back into the container.

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I wish I could say that this was one of the paintings I remember as a kid. I wish I could say that I stood transfixed in front of this painting on one of our many visits to the National Gallery, where my mom’s relationship with the gods of parking allowed us to access the museum with ease. But unfortunately, I don’t remember seeing this painting as a child, even though my mom almost certainly would have shown it to us—yes, because it is a masterpiece, but also because it’s a tangible connection between her and my dad. He was a renowned metallurgist and very much involved in exploring how the world works through experiment and philosophy. She would have appreciated the mystical and ceremonial quality of the painting, with the candlelit setting in particular lending the scene a spiritual air; this effect was all lost on us boys, who were probably running amok in the gallery. I was perhaps like the boy in the painting who is not looking at the experiment but instead fiddling with the window blind, and in doing so letting moonlight into the room. This part of the scene is an intentional reference by the painter to the Lunar Society and the questions being asked at the time about how light travels from the Moon to Earth through space. One of the reasons why something like quintessence had to exist was because it was thought light waves needed a medium by which to travel through space. Sound waves traveled through air, sea waves traveled on water—what was the equivalent medium for space? Scientists called it luminescent aether—renamed because they couldn’t find quintessence.

Brilliant Moments

Meanwhile, the engineers, who had been spending a lot of time making vacuums in glass containers, were getting annoyed at having to continuously pump out the container every time they wanted to do an experiment. What if, they reasoned, once the glass vessel contained a high-quality vacuum, the glass was melted to seal the vacuum inside the chamber. This seal produced a permanent vacuum inside the glass on which to experiment. Of course, you could not move things in and out of the container once it was sealed, so you had to decide what you were going to experiment on and leave it in there. Metal wires could be used, for instance, connected at either end of a glass tube, or glass bulb as it was called. When a voltage was applied, electricity would flow through the tube and the wires would grow very hot, which caused them to glow red. It was the birth of the electric light bulb, an invention deemed so ingenious that the universal symbol for having a brilliant idea is a light bulb.

Early versions in the 1800s emitted light only for a short time, after which the hot glowing wires, called filaments, would then break. Scientists realized that for electric light bulbs to replace candles or gas lamps, the electricity would need to heat up the filament to temperatures exceeding 1,500 degrees. But there was a problem: This temperature exceeds the melting point of most of the metals used to conduct electricity. By the time British chemist Humphry Davy had a go in 1802, the metal platinum was the leading contender, with a melting point of 1,768 degrees. But white-hot platinum vaporized at that temperature quite quickly and so the filaments didn’t last long. They were also very expensive. A cheaper conducting material was needed with a high melting point. (For later filament developments, see “Tungsten’s Brilliant, Hidden History,” March–April 2020.)

The British chemist and inventor Joseph Swan used graphite, which seemed perfect because solid carbon doesn’t melt at all. You have to increase the temperature to 3,642 degrees before it gets so hot it evaporates into a gas, a process called sublimation. Swan took out a patent in 1860, and that should have been the beginning of a bright future. But the difficulty was that carbon reacts very easily with oxygen in the air. Of course, the vacuum inside the bulb should have meant that there was no oxygen. But the early mechanical air pumps did not produce perfect vacuums. They could reduce the air pressure enough to suffocate a bird, kill a mouse, or prevent an insect from flying, but there was still a small amount of air left in the glass bulbs. The oxygen in that air reacted with the carbon filaments and destroyed Swan’s early electric light bulb.

It was not until 1875 that vacuum technology improved enough to create an electric light bulb with a carbon filament that could glow white-hot in a vacuum, providing ample light for 40 hours. Swan started with his own house in Gateshead, then lit a whole street in Newcastle-upon-Tyne, and then the Savoy Theatre in London. It was the future. American Thomas Edison is often credited with inventing the light bulb. He didn’t. What he did was to see that the future of lighting was electric. He perfected the production and marketing of lighting systems, including the bulbs. He is famous for stating that an idea is only a small part of invention: “What it boils down to is 1 percent inspiration and 99 percent perspiration.”

The perspiration in the case of the electric light bulb was the enormous number of experiments Edison performed on different designs of bulb. Most of them failed. But proof of the importance of perspiration and systematic testing was that one of his experimental light bulbs, which seemed to have no use, turned out to be the beginning of electronics and computers.

Mind the Gap

In essence, it was just a light bulb with a broken filament. What Edison’s engineering team noticed was that you could still get electricity to flow through the vacuum, but only if the filament was hot. The electrons would jump across the gap between the broken filament from the negatively charged end to the positively charged end, but not the other way. This discovery was the birth of a component that would kick-start the electronics industry, and it was called a vacuum tube. These vacuum tubes acted as valves, the equivalent of the taps in your kitchen that control water flow. These valves allowed electric signals to be turned on and off by another electric signal (which heated the filament). This design was a programmable tap that could tune and amplify electricity. It led to the development of the loudspeaker, the radio, and the television, the last-mentioned having at its heart one giant vacuum tube, called a cathode-ray tube.

A thousand-year-old quest to create the purest “nothing” still continues, because we as yet can’t even make a vacuum as pure as that found in outer space.

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Cathode-ray tubes have Edison’s hot filaments at one end and a high voltage at the other, where there is a screen. The cathode ray is not a ray of light but a ray of electricity. It literally flies across the vacuum tube, but the only reason it reaches the screen is because there is no gas in the way for the ray of electrons to bump into. When the electricity hits the screen, it lights up because of a special coating called a phosphor. Now there is a bright spot on the screen. To make these TVs work, the ray is scanned across the screen very fast, row by row, so that each part of the screen is hit by the electricity 25 times every second. You would observe this scanning dot if you could see that fast, but you can’t, so instead you see a continuous image of, say, a wizard casting a spell, or a tornado transporting a house through the air. I still remember these TVs from my childhood: We watched films such as The Wizard of Oz on them. They resembled vacuum laboratory equipment because that’s exactly what they were. When you turned the TV off, there was a click and the screen suddenly went blank, except for a single dot in the middle. This dot was the place where the last electrons had hit the screen. The place still glowed for a second before fading to nothing. It was always a sad moment for me and my brothers. The appearance of that dot meant we were going to bed.

TVs in those days were huge, heavy things. They were weighty because the cathode-ray tube was made of glass, and it was not just ordinary glass. A by-product of accelerating electricity to create that dot on the screen is the creation of x-rays, the same x-rays that are used in hospitals to detect broken bones and cancer tumors (and yes, hospital x-ray machines are also vacuum tubes). To protect TV viewers, these x-rays had to be stopped before they escaped from the vacuum tube and radiated everyone watching the TV programs. That meant adding lead to the glass, which absorbed the x-rays. This process worked, but lead, being a very heavy element, increased the weight of the TVs, which were the size of armchairs in my childhood.

Most of these enormous TVs are gone now, freeing up a lot of space in our living rooms but leaving me with a feeling of nostalgia for the simplicity of when we only had three TV channels to watch. They have been replaced by liquid crystal flat-screen technology controlled by silicon chips, with hundreds of TV channels. This materials science invention of silicon chips from the 1950s created the revolution in computing, replacing glass vacuum tubes. Silicon chips are a core technology in every computer, mobile phone, car, washing machine, and piece of hospital equipment. These silicon chips need to be manufactured in ultrahigh vacuums; otherwise, they become contaminated with impurities from the air, which render the chip worthless. Thus a thousand-year-old quest to create the purest “nothing” still continues. And there is still plenty to do, because we as yet can’t even make a vacuum as pure as that found in outer space, which is millions of times purer.

Cleaning Up

For most people, the holy grail of vacuum technology is not their mobile phone, despite its importance and much as they might love it. It’s not the vacuums used in medical technology to produce x-rays, much as they care about its importance for diagnosing illness and tooth decay. It’s not the vacuums used in the scientific equipment in every lab in the world, without which scientific research would come to a standstill. These uses are all too remote and hidden from view to be of daily concern to citizens of the world. No, for most people the most important vacuum in their life is inside their vacuum cleaner. These machines, like the early steam engines, harness atmospheric air pressure created by the hundred kilometers of air above our heads to clean our homes. They create a vacuum inside the machine, which causes air to rush in to equalize the pressure, and in doing so it sucks up dust as the vacuum cleaner kisses the floor. It is so simple, and yet so marvelous. It has made all of our homes less filthy, especially homes with fitted carpets, which would otherwise be dirty, dusty, and smelly. The vacuum cleaner is the stalwart of the home, creating order and cleanliness. It has even played its part in creating more equality between the sexes, making cleaning faster and more effective—freeing time for other things, such as careers and hobbies—and also lowering the barriers to those reluctant to contribute to cleaning the home.

This point brings us back to the search for luminescent aether, the perfect substance, said to inhabit space. By 1905, Albert Einstein’s special theory of relativity banished the need for aether to explain how gravity works and how light travels through space. According to this theory, there is no need for aether, and “nothing” really does exist. It is the creation of nothing inside a vacuum cleaner that harnesses atmospheric air pressure to clean our homes. It’s the nothing inside a light bulb that allows light to emerge. It’s the nothing inside an x-ray tube that helps doctors diagnose illness. It’s the nothing in vacuum chambers that allows us to test the safety of space suits, enabling Felix Baumgartner to safely jump from a balloon on the edge of space. The purer the nothing, the more effective it is. Less is quite literally more, when it comes to a vacuum.

This article is excerpted and adapted with permission from It’s a Gas: The Sublime and Elusive Elements That Expand Our World (Mariner, 2024).