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When is a vacuum a vacuum?

Posted by: roygrif - Sat Nov 20, 2004 4:01 am
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When is a vacuum a vacuum? 
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Post When is a vacuum a vacuum?   Posted on: Sat Nov 20, 2004 4:01 am
The vacuum of space, is it a true vacuum? Surely every time we dump air from a space shuttle into space we are reducing the vaccum? Also, if we dumped a bunch of air into space, where would it travel to?

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Post    Posted on: Sat Nov 20, 2004 8:39 am
The dumped air will mix with the interplanetary and interstellar medium - dust and gases.

The vacuum in space never is and never will be a true vacuum because there allways is the solar wind and the interstellar winds filling the galaxy with gases. There too are the dusts and gases of the comets. Collisions between asteroids are adding dust too.

The solar wind is adding gases of the atmospheres of Venus, Mars and Titan at least.

To create something like a true vacuum special equipment is required as used on earth to create the vacuum in vacuum chambers. But it may be easier to create these artificial vacua in space because there are much less gases outside the chamber that could get into the chamber. A totally true vacuum is physical impossible because of quantum fluctuations as predicted by quantum physics. There allways pairs of electrons and positrons born from nowhere and then again vanishing by destroying each other...



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Last edited by Ekkehard Augustin on Tue Nov 23, 2004 7:46 am, edited 1 time in total.



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Post Re: When is a vacuum a vacuum?   Posted on: Mon Nov 22, 2004 1:47 pm
roygrif wrote:
The vacuum of space, is it a true vacuum?


Answer: no. You can't get a true vacuum. Venus is dispersing its atmosphere into space constantly, as are all the other planets, not to mention the Sun and its Solar Wind. Out in intergalactic space, the atmospheric density is supposed to be around 1x10^(-33) molecules per cubic meter, which is pretty low (I've got the actual figure in my backpack, but don't feel like finding it right now).

roygrif wrote:
Surely every time we dump air from a space shuttle into space we are reducing the vaccum? Also, if we dumped a bunch of air into space, where would it travel to?


Try putting a few drops of food coloring in water, and DON'T stir it. Leave it alone for a while, and watch what happens. Given enough time, the food coloring will dissolve through the water.

What did this prove? Although a local disturbance in the pressure was caused by the food coloring, it soon evened itself out by dissolving throughout the solution.

The pressure change will equal itself out very rapidly. You'd have to dump absolutely insane amounts of air right into your face to be able to breathe without a pressure suit.

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Post    Posted on: Mon Nov 22, 2004 7:12 pm
The only "true" vacuums that exist are ones we've made in the labs, and even those only work on a tiny scale. We generally refer to anything above the bulk of the atmosphere as a vacuum, however you will still find at least millions, and probably billions of gas particles per litre in space.

If you travel outside the solar system, the "air" will thin about another ten to a hundred times, and if you leave the galaxy, it will thin out by that much again. But even out there, it isn't a perfect vacuum, just a lot lower pressure than what we are used to.

There are about 10^22 molecules in a litre of air. A thousand times lower pressure still leaves a lot of molecules.

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Post    Posted on: Wed Dec 01, 2004 8:14 pm
That's what I assumed. We really shouldn't call it a vacuum. Just super low-pressure.

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Post    Posted on: Fri Dec 03, 2004 12:02 pm
roygrif wrote:
That's what I assumed. We really shouldn't call it a vacuum. Just super low-pressure.

Hmm that reminds me, I have to change the filter on my super low-pressure cleaner when I get home tonight.

Perhaps using the terms "vacuum" and "true vacuum" are just fine.

DKH

I always liked the word vacuum ... when I was a kid I liked that it looked sorta like varooom! and so, as a word, I thought it was pretty cool.

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Post    Posted on: Mon Dec 06, 2004 5:18 pm
Sev wrote:
The only "true" vacuums that exist are ones we've made in the labs, and even those only work on a tiny scale. We generally refer to anything above the bulk of the atmosphere as a vacuum, however you will still find at least millions, and probably billions of gas particles per litre in space.

If you travel outside the solar system, the "air" will thin about another ten to a hundred times, and if you leave the galaxy, it will thin out by that much again. But even out there, it isn't a perfect vacuum, just a lot lower pressure than what we are used to.


I am pretty sure the best vacuum we can make on Earth is still not as good as outer space. I recall reading somewhere that astronomers estimate there is about one hydrogen atom per cubic centimeter in intergalactic space. Of course at the Earth's distance from the sun the solar wind density is much higher. And at LEO the upper atmosphere density is even higher.


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Post    Posted on: Mon Dec 06, 2004 6:04 pm
Space is not a pure vacuum... How can it be? It's got all kinds of planets and stars and comets and aliens and a lotta other stuff littering it.

:lol:

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Post    Posted on: Mon Dec 06, 2004 6:31 pm
Well there you answered it. With all that stuff it isn't completely empty like a REAL vacuum would be.
:lol: :lol:


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Post    Posted on: Fri Dec 10, 2004 11:43 pm
I must say I'm enjoying the great info and outside the box thinking that goes on on this site. To my best knowledge 30 inches hg of vacuum is the physical limit, My plant makes on average 27.5 to 29 on a every day basis, this is done by rapid condensation of super heated steam {960d} with the exception of the noncondensable gases that make it through the system. <>%xload, Makes me think of the old bumper sticker "there is no gravity! the earth sucks" I got a laugh out of that one. But back to the Q , As I understand it and was already answered above anything below normal atmopheric pressure is by definition considered a vacuum. I'm sure the 30hg can be challenged at some point with the presence of a big black hole. :idea:


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Post    Posted on: Sat Dec 11, 2004 7:49 pm
Hello, author,

your answer is a ally philosphical one - implicitly. Vacuum as emptyness, vacuum as empty room, vaccum as empty space - and: Has Earth to be considered to be a part of the space or has it not? Is vaccum absence of gases only or absence of dust, atoms and particles too? Seem to be difficult questions physicists never seemedd to have asked - they simpli are stating that allways electron-positron-pairs are fluctuating into and out of each vacuum.

This turns the thread to be a chance of huge creativity, doesn't it?



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