# How is Space a vacuum?

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I’m having a hard time understanding this. From what I have read, a vacuum is a space that is devoid of matter. But there is matter in Space (planets, chemical compounds, stars, etc.). There is something I’m missing here and I’m not understanding

In: Physics

The planets, stars etc. exert a gravitational pull and “grab” all the matter near them, so there is next to nothing in between the object and that next to nothing is the near vacuum of space.

Well, you don’t count the stars and planets. Pick a cubic meter a long way from anything visible, and there will be a few molecules of gas in it … but not many.

If you put a ping pong ball in a glass box and suck all the air out the ping pong ball will remain. In space it’s the same concept.

You can think of it this way. Space is a vacuum (mostly, there’s still bits of hydrogen and space dust floating about but it’s pretty close) and space contains planets and stars and stuff, but space itself isn’t made up of planets.

As an analogy a glass jar is made up of glass, and if you fill it with water the jar contains water, but you wouldn’t say that the water is part of the jar.

Neil deGrasse Tyson made a GREAT video on the concept of nothing. Basically, even in space, there’s always something.

But the reason it’s a vacuum is because there’s no pressure or less pressure than on say earth. Ever notice when you have just one or two windows open in your home, and you shut the door of the room the window is in, and the door just slams? That’s because there’s less pressure outside your home than inside, and the air being moved from your door shutting escapes more quickly, thus creating a vacuum effect.

Same goes for space. It’s really just pressure difference. Pocket of air introduced to a space with no air, the air will rush into the space with no air, thus, a vacuum is formed.

You’re not really missing anything, it’s just a matter of semantics.

We typically ignore the places where matter has clumped together due to gravity – ie. celestial objects like stars, planets, moons, asteroids etc. But whether you exclude those objects or not, space is just so massive and close enough to empty that it is, for all intents and purposes, a vacuum. It’s not a *perfect* vacuum though.

I think maybe there is some confusion between the definition of “space” and “vacuum.”

The word “space” doesn’t *specifically* refer to the emptiness between the planets and stars. “Space,” in the astronomical sense of the word, refers to the three dimensional place in which things exist. It’s all “space.” You’re in space right now.

The distinction is that **most of that “space” is in** ***vacuum***. “Vacuum,” loosely refers to “space” that doesn’t contain matter. I say “loosely” because a perfect vacuum is a very rare thing. For a vacuum to be perfect, the designated space has to be devoid of *all matter particles and protons.* That’s impossible to do experimentally.

Space has an average of 1 atom per cubic centimeter. It’s important to remember that that number is an average, so there are areas of space that contain *much less* than that (like in deep intergalactic space,) and areas that contain *much more* than that (like in-between the planets in our solar system.)