vacuum in space

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For the physicists or the well informed out there. I've never gotten a satisfactory answer to this question: if in the vacuum of outer space you attempted to extend the plunger of a syringe or draw on a straw whose end is blocked off, what would happen? Would they collapse as if under atmospheric pressure? Or could the plunger freely extend without drawing anything into the tube? Could you freely pull two plungers away from each other in a tube from a fully collapsed against each other position?
 
In fact, if the plungers were two perfect, plane, parallel mirrors separated by 10nm (about a hundred times the typical size of an atom) the Casimir effect would produce the equivalent of 1 atmosphere of pressure.

The Casimir effect is of no consequence at the distances we deal with in everyday life, but it is important in nanoscale structures and micromechanical systems.
 
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There are radiation, dust and gas in space, more concentrated in some areas than others.
Of course, as are billions of stars and anything else taking up space. What I can't get my head around is the absolute nothingness when that entity, whatever it may be is taken out of it's place without anything else rushing in. Hence my question about the syringe.
 
Could you freely pull two plungers away from each other in a tube from a fully collapsed against each other position?
rayma has explained that, in a vacuum, the plungers could be moved freely apart since there would be no atmospheric pressure pushing them together.

As to what would be between the plungers after they are pulled apart, the answer is a vacuum - or more correctly a quantum vacuum!

P.S. This would be equally true if you tried to pull the plungers apart in the Earth's atmosphere or in outer space.

The first man-made vacuum was produced by Torricelli. He filled a long glass tube, closed at one end, to overflowing with mercury. He then sealed the open end with his finger and inverted the tube in a dish of mercury.

Upon removing his finger, some mercury fell out of the tube into the dish leaving a space at the top of the tube. A column of mercury around 760mm high remained in the tube, supported by the immense pressure of the atmosphere pushing down on the surface of the mercury in the basin.

He found that the height of the mercury fluctuated with changes in atmospheric pressure - he had made a mercury barometer!

But the salient question for us is - what is left in the space at the top of the tube after some of the mercury has fallen into the dish?

The answer, just like in your scenario of separating the two plungers, is that the space contains a vacuum! (Well, not an absolute vacuum in the case of the mercury barometer as there will be traces of mercury vapour present.)

I hope the above information proves helpful in visualising the vacuum.
 

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There was an interesting Podcast on the radio a while back (available UK only I think):

BBC Radio 4 - The Life Scientific, Ewine van Dishoeck on cosmic chemistry

where it was mentioned (around 5 minutes in) that a dense interstellar cloud had the order of 10,000 particles/molecules per cubic centimeter, and that the best man made ultra high vacuum was around 100,000,000 (100 million) particles/molecules per cubic cm.
 

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Further to Mooly's contribution, at ultra-high vacuum there can be as few as 26,500 molecules per cubic centimeter.

At this density, there is only one molecule roughly every 0.33 mm in space.

The Fundamentals of Vacuum Theory

Would it help if I said there is no such thing as an empty space - no such thing as an absolute vacuum?

Think of your space as a region where the pressure is so low that any particles it contains have no effect on what's going on in there.
 
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