In The Private Journal of Henri Frederic Amiel, the famed philosopher stated that “Uniformity [..]creates a void, and Nature abhors a vacuum.” However, most astronauts have probably been aware of the fact that their surroundings are, in fact, a vacuum.

This then might beg the question, “why is there a vacuum in the first place?”

First, lets get rid of a misconception. When you think of a vacuum, one generally thinks of something with a lack of air. One fun way to try this is to take an empty bottle and just try sucking all of the air out. If you could do that perfectly (spoiler alert, you can’t), you would creat a vacuum inside the bottle, which makes it stick to your lips. As long as the mouth of the bottle doesn’t have any spaces between it and your lips, it will give you the ability to swing it around with your head as you please, also giving you the ability to attract annoyed stares from your wife.

However, if you think of it way, space is not a true vacuum; there really isn’t such a thing as a vacuum.

Emptiness

The word stems from the Latin adjective vacuus for “vacant” or “void”, however, there is a whole lot of stuff actually filling space what we consider the vacuum of space.

“(W)hen we say outer space (the space outside the atmosphere of planets and stars) is a ‘vacuum’ or is ‘empty’, we really mean that outer space is nearly empty or almost a perfect vacuum,” explains Dr. Christopher S. Baird, an Assistant Professor of Physics at West Texas A&M University, in his blog Science Questions with Surprising Answers.

“In reality, even the most remote spot of outer space has gas, dust, radiation, gravity, and a whole host of other things. There is no such thing as truly empty space. If we tried to suck all the particles out of a certain volume, we could still never get it empty. There would still be things like vacuum fluctuations, gravity, and dark matter, which can’t be sucked out. With that said, outer space is very close to empty compared to earth’s atmosphere.”

Ancient Greeks had some interesting ideas about vacuums — as they did with most things. They didn’t know what an atom was, but they considered the idea of atomism: small things that fill everything. The abstract concept of a truly empty void was regarded with skepticismm, even as Plato lent some support. His disciple Aristotle believed no void could occur naturally, because the denser surrounding material would simply fill up the setting

Almost two thousand years after Plato, René Descartes also proposed a theory similar to atomism, but without the problematic matter of the void. Descartes also agreed with the contemporary position that a vacuum does not occur in nature.

Yet to this day, the idea of a vacuum remains somewhat uncertain among physicists — especially with concepts such as dark matter and dark energy in the mix.

Making a vacuum

This still hasn’t exactly answered the question of “what causes the vacuum” though.

The short answer is that in the void of space, the pressure is so low that all molecules want to spread out as much as possible. This expansion, in turn, creates the vacuum that we all know to exist, and is also what leads to the development of the stars and planets that we see in our night sky.

Because outer space has very low density and pressure, it makes something very close to a vacuum — but it’s still not a perfect vacuum. Even in interstellar space, there are still a few hydrogen atoms in every cubic meter.

“Every particle of matter, no matter how small, exerts a gravitational attraction on all other particles of matter,” says Baird. “Given enough time, gravity makes giant clouds of gas in space condense down despite the gravitational force being so weak. Soon after the Big Bang, the universe was filled with a nearly uniform soup of hydrogen and helium. Over billions of years, gravity pulled most of these gas atoms into stars. Inside the nuclear furnace of stars, hydrogen and helium were fused to form the heavier elements up to iron.”

Larger stars will eventually die in an explosive supernova creating all the naturally occurring elements heavier than iron and spewing these elements into space. Over the course of time, the heavier elements condense down under gravity to form small clouds and rocks. In turn, the clouds and rocks are gravitationally attracted one other which will form asteroids, moons, and planets. Space is mostly empty because matter that used to be out there has fallen into an asteroid, planet, moon, or star under the influence of gravity.

Another misconception is that exposure to a vacuum leads to instantaneous death. Being exposed to the vacuum can actually be survivable, albeit very uncomfortable.

A 1965 study by scientists at the Brooks Air Force Base in Texas showed that dogs exposed to near vacuum—one three-hundred-eightieth of atmospheric pressure at sea level—for up to 90 seconds always survived, however, during the exposure, they were rendered unconscious and paralyzed.

They also experienced serious discomfort as gas expelled from their bowels and stomachs caused simultaneous defecation, projectile vomiting and urination while also suffering massive seizures. Their tongues were often coated in ice and the dogs swelled to resemble “an inflated goatskin bag,” the authors wrote. But after slight repressurization the dogs shrank back down, began to breathe, and after 10 to 15 minutes at sea level pressure, they managed to walk, though it took a few more minutes for their apparent blindness to wear off.

“In any system, there is always the possibility of equipment failure leading to injury or death,” says Dartmouth Medical School professor and former NASA astronaut Jay Buckey, author of the 2006 book Space Physiology. “That’s just the risk you run when you are in a hostile environment and you depend upon the equipment around you. But if you can get to someone quickly, that is good. Often spacewalks are done with two spacewalkers and there is continuous communication. So if someone is having a problem, hopefully the other can go get them and bring them in.”

A real-life example occurred in 1966 when NASA engineer Jim LeBlanc was accidentally exposed to a near zero vacuum.

The space suit he was testing experienced a rapid loss of suit pressure due to equipment failure. He recalled the sensation of saliva boiling off his tongue before losing consciousness.

When the chamber was rapidly repressurized, LeBlanc regained consciousness quickly and went home for lunch. Another man was accidentally exposed to vacuum in an industrial chamber; it was at least three minutes before he was able to be repressurized. He required intensive medical care, but eventually regained full function. These instances show that ebullism — the formation of gas bubbles in bodily fluids due to reduced environmental pressure — is not inevitably fatal and the body can hold together just fine…at least for a few seconds.