Space is a near-perfect vacuum, brimming with cosmic gaps. In other words, Gravity is to blame. But, to comprehend our universe’s vacuum, we must first understand what a vacuum is — and what it isn’t.

So, what is a vacuum, and why isn’t space a very vacuumed environment?

To begin, Jackie Faherty, a senior scientist in the Department of Astrophysics at the American Museum of Natural History in New York City, told Live Science that the vacuum cleaner is not a good comparison for the vacuum of space. The vacuum cleaner successfully fills itself with dirt and dust collected from your carpet. (The vacuum cleaner creates suction by using differential pressure.) A suction cleaner (rather than a vacuum cleaner) is a better name. On the other hand, the vacuum of space is the polar opposite. A vacuum, by definition, is empty of matter. Space is almost completely devoid of air, not due to suction, but practically empty.

Because of the vacancy, the pressure is exceedingly low. While it’s difficult to replicate the nothingness of space on Earth, scientists can generate partial vacuums, which are very low pressure settings.

“Understanding the notion of the vacuum is nearly strange because it is so antithetical to how we live,” Faherty said, even without the vacuum cleaner comparison. As humans, we are fully bound to a small, crowded, and dynamic portion of the cosmos. As a result, she said, it might be difficult for us to comprehend nothingness or emptiness. But, in truth, what we consider typical on Earth is unusual in the context of the cosmos, which is practically empty for the most part.

Gravity is supreme.

Even if we didn’t have Gravity, space would be relatively empty on average. According to Caltech theoretical astronomer Cameron Hummels, “there’s simply not a lot of material proportional to the volume of the cosmos in which you place those things.” According to NASA, the average density of the cosmos is 5.9 protons (a positively charged subatomic particle) per cubic meter. On the other hand, Gravity accentuates the emptiness in particular parts of the universe by driving stuff to gather.

In general, any two mass objects will be attracted to one other. That’s how Gravity works. To put it another way, “matter like to be with other matter,” according to Faherty. Gravity pulls neighboring things closer together in space. Their aggregate mass grows, and with increased mass comes the ability to produce a stronger gravitational pull, attracting even more matter to their cosmic cluster. Mass rises first, followed by gravitational force, and finally mass. “It’s a domino effect,” Hummels said.

According to Hummels, the space between these gravitational hot spots is evacuated as the neighboring matter is drawn in, producing a cosmic gap. However, the cosmos did not begin in this manner. The substance in the cosmos was scattered more equally after the Big Bang, “almost like a fog,” he added. However, Gravity has collected that stuff over billions of years into asteroids, planets, stars, solar systems, and galaxies, leaving gaps of interplanetary, interstellar, and intergalactic space between them.

Even space’s vacuum, though, is not pure. There is fewer than one atom in every cubic meter between galaxies, implying that intergalactic space isn’t empty. It does, however, contain significantly less matter than any vacuum that humans could create in a lab on Earth.

Meanwhile, “the universe continues to grow,” Faherty remarked, ensuring that the universe would stay essentially empty. She said, “It sounds very lonely.”

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