Space is an almost perfect vacuum, filled with cosmic voids. And briefly, gravity is responsible . But to actually understand the vacuum of our universe, we’ve to take a moment to know what a vacuum really is — and what it isn’t .
So, what’s a vacuum, and why isn’t space a real vacuum?
First, forget the vacuum cleaner as analogy to vacuum of space, Jackie Faherty, a senior scientist in Department of Astrophysics at the American Museum of Natural History in NW City. The household cleaning machine effectively fills itself with dirt & dust sucked out of your carpet. (That is, the vacuum uses differential pressure to make suction. Suction cleaner could be a far better name than vacuum cleaner). But the vacuum of space is that the opposite. By definition, a vacuum is barren of matter. Space is nearly an absolute vacuum, not due to suction but because it’s nearly empty.
That emptiness leads to a particularly low-pressure . And while it’s impossible to emulate the emptiness of space on Earth, scientists can create extremely low-pressure environments called partial vacuums.
Even with the vacuum analogy out, “understanding the concept of the vacuum is nearly foreign because it is so contradictory to how we exist, Faherty said. Our experience as humans is totally confined to a really dense, crowded & dynamic fraction of the universe. So, it are often hard for us to actually understand nothingness or emptiness, she said. But actually , what’s normal for us on Earth, is really rare within the context of the universe, the overwhelming majority of which is almost empty.
Gravity is king
On average, space would still be pretty empty even if we did not have gravity. “There’s just not tons of stuff relative to the volume of universe in which you set that stuff,” according Caltech theoretical astrophysicist Cameron Hummels. the avg. density of the universe, consistent with NASA, is 5.9 protons (a charged subatomic particle) per cubic meter. On the other hand gravity amplifies the emptiness in certain regions of the universe by causing the matter in universe to congregate.
Basically, any 2 objects with mass are going to be interested in one another . That’s gravity. Put differently, “matter likes to be around other matter,” Faherty said. In space, gravity draws nearby objects closer together. Together their collective mass increases, and more mass means they will generate a stronger gravitational pull with which to draw even more matter into their cosmic clump. Mass increases, then gravitational pull, then mass. “It’s a runaway effect,” Hummel said.
As these gravitational hot spots pull in nearby matter, the space between them is evacuated, creating what’s referred to as a cosmic void, Hummel said. But the universe didn’t start that way. After the Big Bang, the matter in universe was dispersed more uniformly, “almost like fog,” he said. But over billions of years, gravity has gathered that matter into asteroids, planets, stars, solar systems & galaxies; and leaving between them the voids of interplanetary, interstellar & region.
But even the vacuum of space isn’t truly pure. Between galaxies, there is less than one atom in every cubic meter, meaning intergalactic space region isn’t completely empty. It’s far less matter, however, than any vacuum humans could simulate during a laboratry on Earth.
Meanwhile, “the universe keeps expanding,” Faherty said, assuring that the cosmos will remain mostly vacant. “It sounds so lonely,” she said.