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We get told "there is nothing in space except planets etc.." (saying there is no air etc) but is there "nothing"?

If there is it must be a strong vacuum and how strong will it be? could we use it for more efficient travel? A vacuum pulls, so where is it "pulling" to, it doesn't seem to "go" anywhere?

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  • $\begingroup$ "..but is there "nothing"?" Not that it makes a difference to the correctness of the answer by @BlakeWalsh, but no, it is not really completely nothing. As we leave Earth the atmospheric pressure drops off rapidly, but the ISS at 400 km altitude is still slowed by the outer tendrils and needs occasional boosts. Then we enter stellar space where the heliosphere has a significantly lower density, then it drops again in interstellar space, interstellar voids, and intergalactic space. $\endgroup$ Sep 24 '15 at 9:51
  • $\begingroup$ Compare Aether (classical element), particularly the section Aether and light. $\endgroup$
    – user
    Sep 24 '15 at 11:19
  • $\begingroup$ Vacuum doesn't pull; air pushes. If you create a vacuum at sea level, what you feel isn't the vacuum pulling, but the pressure of the atmosphere trying to fill it in. $\endgroup$
    – ToxicFrog
    Sep 24 '15 at 13:05
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    $\begingroup$ It should be asked in physics.SE $\endgroup$
    – Manu H
    Sep 24 '15 at 13:09
  • $\begingroup$ You can find a basic answer to some of these questions by reading the opening paragraph of the wiki articles on Outer Space, Vacuum, and Vacuum state. As it is, this question is too broad to be answered appropriately here. And I have a feeling that a refined question would look a lot more like a question that belongs on Physics SE and already has an answer there. $\endgroup$
    – called2voyage
    Sep 24 '15 at 14:11
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I'll give a simple answer.

An ideal vacuum is simply nothing. It does not pull, it exerts no force on objects. Within a vacuum, far from a gravitational field, objects in motion simply travel in a straight line, the vacuum exerts no force, no resistance, upon the object.

I'm speculating that the idea of "pulling" comes from "explosive decompression" seen in movies, what happens is that atmosphere within a spaceship is pressurized, it is pressurized by the walls of the spaceship which are strong enough to hold the air pressure. Pressure is related to the velocity of molecules within the gas, in air at room temperature and standard atmospheric pressure, the molecules are travelling very fast, about 500m/s, this is 1800km/h or 1100mph (google "speed of air molecules"). All these molecules are zipping around at tremendous velocities and bouncing off each other and solid objects, because the particles are so tiny and there are so many of them and they are bouncing off us from all sides the force evens out, and we just know it as "pressure", which normally we don't even notice.

So in the spaceship, there are all these molecules zipping around at 1800km/h, but being contained by the walls. Then something makes a hole in the wall, suddenly the particles are free to shoot out the hole at 1800km/h. And that is exactly what happens, all the particles which would have bounced off the wall, instead shoot out the hole and travel off into space at 1800km/h.

Please note that "explosive decompression" as seen in movies doesn't happen in reality. You can't get sucked out of a hole. In fact, you could plug a hole with your finger. Rather it's just like I described it above, the air molecules which would have been contained by the wall, instead shoot out into the vacuum, so the air gradually escapes, as air escapes it will create a low pressure zone near the hole, which then creates a wind towards the hole. But it would not be explosively violent.

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Just to answer your last point. A vacuum on Earth can have an effect, but only because of the pushing of the Atmosphere back to fill that hole. It's the difference in pressure that makes the difference, not anything else. You would have the same effect increasing the outside pressure as decreasing the inside pressure.

As far as Explosive Decompression, it can be mildly damaging. See this Mythbuster's clip.

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Space is not a perfect vacuum. Within the solar system, you can expect about 100 particles/cm$^3$. This ranges from individual atoms to very small dust particles.

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