# If space is a vacuum, what causes that vacuum?

Since there is no oxygen in space and no gravity, what causes this "vacuum?

The expansion of space? I guess I am hitting upon the "turtles all the way down" theory here, but I still am curious.

A vacuum is by definition the absence of air. So you’re begging the question. What else would cause a vacuum? There’s just nothing filling up the space.

Well, there is gravity in space. But really, the question is why most of the matter in the universe is clumped up in stars, leaving big empty spaces in between. And the answer that would be gravity: the matter attracts other matter, and clumps up, then starts attracting other matter. Once it’s become a large clump of matter like a star, it’s very hard for the matter to escape into space, because of gravity.

(And this clumping up has been taking place over a very long period of time).

Hmmm, I don’t even know where to start with this question.

OK, vacuum isn’t “caused” by some force. Yeah, your vacuum cleaner needs power to suck up dirt. But that’s because there’s all this air on Earth, and so we need energy to create a vacuum here. It takes energy to move all those oxygen and nitrogen molecules from one place to another. And the lack of vacuum on Earth is caused by gravity. Without gravity pulling them down, those molecules of air would float off into space.

Now, space. It doesn’t take energy to create a vacuum in space, because there’s already a vacuum. Meaning, a couple of atoms every cubic meter or foot or inch. No force is needed to create this vacuum, because you don’t need to pump molecules out of it (like you do on Earth), they were never there in the first place.

It’s like asking what force keeps deserts so dry. They’re not dry because some mysterious force keeps removing the water, they’re dry because it hardly ever rains there.

Empty space would be the absence of anything and everything.
There is supposed to be approximately one atomic hydrogen atom to 15 molecules of hydrogem per cubic meter of space IIRC.

Vacuum doesn’t need a cause. When you don’t have a vacuum, that’s when you have to ask why.

There’s a vacuum because the 17th century philosophers had it backwards:

Nature abhors a pressure.

Nature’s not that fond of true vacuums, either, but she can be satisfied with extremely rarefied particle distributions.

I don’t think I’ve understood your question.

Why do you think that a vacuum could be explained by the presence of oxygen and/or gravity?

-FrL-

The vacuum is caused by humans thinking the high pressure in their tiny local environment makes the low pressures in 99% of the universe unusual.

Sorry I didn’t make myself more clear. I guess what I’m trying to say is, how can something be declared a vacuum if the matter that is sucked into the vacuum has nowhere to go?

I’m a little confused at what I’m trying to say as well, so bare with me.

I’ll think on what I’m really asking and get back to ya.

Gravity is one reason, but another reason is that the universe is expanding so there is more space being created all the time, this new space contains no matter.

[b}diggleblop**, I refuse ta bare with you.
What I said was tongue-in-cheek, but there’s a kernel of truth in it. Nature doesn’t like for pressure to be built up in some places while it’s absent in others. That pressurized item will tend to lose its pressure unless something is holding it in (gravity, a big steel tank, whatever). and even then it’ll leak, if it’s at all possible (atioms kicked off into space from the top of the atmosphere, gas finding its way through cracks or joints in the container).

if i take a balloon into space it’ll blow up bigger than it was on the earth’s surface, because there’s less pressure from the outside pushing in. It’ll probably get so big it pops. Or eventually, it’ll all leak out. Now those air molecules spread out over a larger volume. If spasce was pretty small, say twice the size of the ballon, there’d now be a lower pressure everywhere. But it’s not. Space is unbelievably big. Even if you only consider the space within the solar system, which your molecules probably aren’t going to escape from. Heck, if you only consider the space in your building (if it were otherwise vacuum), the addition of one balloonfull of air isn’t going to noticeably raise the pressure above vacuum.

It’s not a question of what sucks something out to cause vacuum. evenly distributed gas molecules throughout the universe would conzstitute pretty damned good vacuum. You only notice the presence of non-vacuum when something is working to keep the gas together in one place, like a planet, or a space ship. or a balloon.
That giant sucking sound isn’t jobs going to Mexico. It’sd the inexorable drive of entropy trying to spread the molecules around evenly like butter on bread.

OK, stop thinking about vacuums sucking. Vacuums don’t suck. As CalMeachem points out, vacuum doesn’t suck, air pressure blows.

What creates air pressure? A bunch of air (which is oxygyen and nitrogen) molecules bumping around. So when you get a hole in your spaceship, the vacuum doesn’t suck the air out of your ship, the air inside blows out…just like the pressurized air inside a balloon blows out when you let go, and the balloon zooms around the room. We don’t think of the one atmosphere air sucking the high pressure air out of a balloon, do we? Same thing with a spaceship. The air in the balloon or the spaceship blows out until there is the same amount of pressure inside and outside. For the balloon on Earth, that equal pressure is one atmosphere of air. For the spaceship, that pressure is hard vacuum.

The air that blows out into the vacuum very very very slightly raises the pressure in around the spaceship…but there is so much empty space and so little air inside a spaceship that pretty soon you’d need sophisticated instruments to detect the tiny increase in average density. And pretty soon after that you wouldn’t detect anything.

For Earth, what holds the air in isn’t a spaceship hull, but rather Earth’s gravity. A little bit of air leaks out all the time, but very little. So there’s a force that creates pressurized air, namely gravity. Without that force the air would leave the Earth and zoom out into space, creating a tiny tiny tiny bit more molecules per square meter of space. Yes, there are trillions and trillions of oxygen and nitrogen molecules in Earth’s atmosphere, but there are vastly more cubic meters of vacuum out there in the universe than there are molecules of air on earth. It would be like adding one drop of spit to the Pacific ocean. Less than that.

A vacuum isn’t a process, it’s a condition.

Space isn’t a vacuum because anything is or isn’t happening. Space is or isn’t a vacuum simply because of what happens to be in it.

OK, OK, so most of the universe is what is called “hard vacuum” which is not the same as a perfect void. Close enough for government work, though.

digglebop seems to be confused by the observational/experiential frame of reference of vacuums. But as was mentioned before, the total amount of matter in the universe is such that if evenly spread it would be still pretty thin. Add to that how (very broadly) gravity causes matter to clump together, and what’s left between those clumps is pretty much hard vacuum.

He does, though, make bring up an interesting notion by mentioning expansion – in the extreme early phases after the Big Bang, would existence at any point have been sufficiently “densely packed” with primordial particles for the universe to be considered “pressurized”? Or would it be understood that by the time the particles became anything for which “density” and “pressure” can have any meaning at all, the universe would have inflated so far that for all intents and purposes you had a near-vacuum from the start?

We’ve got plenty of nuthin’? :dubious:

Astrophysicists step in.

I seem to recall (which is becoming my favorite phrase) that the entire mass of the universe can threoretically be compressed into a size the head of a pin. That is the theory behind the “Big Bang”. The mathematics work down to something like a trillionth of a second then the theory breaks down. Therefore, the creation of the universe is still not really understood.

That’s the pedestrian explanation as I got it.

If that is the case, then a huge amount of space with barely anything in it becomes a logical condition.

OK, now flame me and tell me what an idiot I am. I’m just trying to help.

Working the math backward to show that the mass of the universe must have been in a smaller volume just after it came into existence is not the same thing as saying that it “can theoretically be compressed into a size the head of a pin.” The conditions at that time, when all the fundamental forces were united and no particles as we understand them existed, are hard to translate into any commonsense terms. I think bringing it up in this discussion just confuses the issue. Maybe you should start a new thread if you want people to discuss it.

Just trying to give some basic concept of vacuums and why the universe isn’t filled with atoms or particles as they are commonly conceptualized. Sorry if it offends your knowledge of theoretical physics. I tried to be as unassuming as possible.