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Is there a perfect vacuum between atoms in space?

  1. Jul 28, 2010 #1
    As the title states, if I go to space and detect several atoms per square meter of space, does this suggest that the space between these atoms is essentially void of all forms of matter? Thus is this a perfect vacuum?
  2. jcsd
  3. Jul 28, 2010 #2

    Vanadium 50

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    Of course the same thing is true on earth - the space between atoms in the atmosphere is also vacuum.
  4. Jul 28, 2010 #3
    So when I was told a perfect vacuum is impossible, I was told a lie?
  5. Jul 28, 2010 #4
    There is no perfect vacuum because you can't obtain zero pressure. Pressure is a macroscopic quantity of course, it doesn't make sense to say that there is zero pressure between atoms. If you measure the pressure in space, it will not be zero because there are atoms present. If you specify a certain region and try to isolate it in some way while all the atoms are elsewhere, you can't do that...
  6. Jul 28, 2010 #5
    Hi there,

    More or less. You have perfect vacuum at microscopic distance.

    However, it is very hard, if not impossible to have a perfect vacuum of long distance.

    That's it.

  7. Jul 28, 2010 #6


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    The way we make vacuum on Earth is ostensibly to suck all the air out of a vessel. This is a misrepresentation. There is no such thing as suction.

    What really happens is that the internal pressure of the vessel is caused by gaseous atoms bouncing around. When we open the valve and turn on the pump, most of those atoms (because they are bouncing off the walls and off each other) will ultimately fly up the tube and out.

    Eventually though, the vessel will reach a very low pressure. The atoms are free to bounce around inside the vessel but they are no longer bouncing off each other. There is no reason why they will fly up the tube except by chance and patience.

    The upshot is that you can never get those last few atoms out. The atoms per cubic metre will drop towards zero but never reach it in any reasonable time frame.
  8. Jul 30, 2010 #7
    So chill the walls. Next "bounce", the atom becomes frost.

    Or, start with a solid with no gap, and introduce a gap by moving parts away from each other. This can be done easily with mercury, for example.

    There are other ways of producing vacuum that don't have the same specific limitations.
  9. Jul 30, 2010 #8
    Don't forget the constant flow of neutrons everywhere!

    And randomly flying free electrons!

    And muons!

    And them virtual matter-antimetter pairs that spontaneously create themselves out of gamma rays and can cause Hawking radiation if they happen to appear at the event horizon of a black hole!

    And more!...

    There in no complete vaccum. But these examples, while matter, don't necessarily interact with atoms, so we can often overlook them.
  10. Aug 2, 2010 #9
    Hi there,

    Alright, but what about all the space between the flowing neutrons, electrons, muons, and neutrinos. There is still a great amount of space left, and therefore, empty space left.

  11. Aug 2, 2010 #10
  12. Aug 2, 2010 #11

    D H

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    Read up on sublimation.
  13. Aug 2, 2010 #12
    Even when there are no particles in a space, there is still the chance that a 'vacuum fluctuation' will cause a particle and anti-particle pair to emerge spontaneously, with only one of them being in the volume under consideration.
  14. Aug 2, 2010 #13


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    "The atom becomes frost??" I know you're playing fast & loose with physics here, so I'll roll with it, but how does a slower moving atom result in vacuum?
  15. Aug 2, 2010 #14
  16. Aug 2, 2010 #15
    we would also have the energy from the G field . And also i can't think of a place in space that you couldn't see a star . all tho their might be one .
  17. Aug 2, 2010 #16


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    What does this have to do with the question being asked???

    Oh, I got it now. Your comment presumes that the volume of interest need be energy-free.

    No, a vacuum does not need to be free of energy; it need only be free of matter.
  18. Aug 2, 2010 #17
    I've been following this and I thought I was clear on the answer until I got to thinking...

    What about the space in between virtual particles? I understand that they don't have a fixed position. I mean is there such a thing as a space so small it precludes the existence of virtual particles?
  19. Aug 3, 2010 #18
    No. See Casimir's force.
  20. Aug 3, 2010 #19
    The Casimir effect is an energy effect. As mentioned earlier in this thread, a vacuum need not be devoid of energy, only matter. The Casimir effect, as I understand it, requires the presence of matter to be observed.

    I'm considering a volume of spacetime that is too small for a virtual particle to "pop" into. If the Casimir effect forbids such a small volume from existing, could you please explain to me why. Thanks!
  21. Aug 8, 2010 #20
    @Vanadium 50: Excellent point.

    Don't forget there's empty space between the nucleus and the electrosphere too.
    One of the most puzzling questions I've ever been asked was "According to Rutherford, atoms are big empty spaces. So even a wall is, mostly, space. Why can't we cross it?"

    I think when someone who isn't a specialist talks about vacuum, he means "an empty macroscopically-sized space". If we stick to this meaning, then the perfect vacuum only exists between interstellar space - if, of course, it is not disturbed by all the particles previous posters have listed.
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