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Illegitimate source that there is no such thing as a true vacuum

  1. May 25, 2009 #1

    Mentallic

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    I have heard from an illegitimate source that there is no such thing as a true vacuum. I just want to confirm this statement true/false and why so if it is true. Thanks.
     
  2. jcsd
  3. May 25, 2009 #2
    Re: Vacuums

    Where did you hear this from? I too have heard the mention of things such as this, also that nothingness contains a quantum ammount of spacial value as well. Both of which were from also, illegitimate sources.
     
  4. May 25, 2009 #3

    Mentallic

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    Re: Vacuums

    https://www.physicsforums.com/showpost.php?p=2211690&postcount=23"
    Not meaning to insult the poster, I'm just trying to silence my suspicions :biggrin:

    Hmm, that also sounds perplexing, but what is
    ?

    But really, I wouldn't understand why there could be no such thing as a perfect vacuum in a container. Maybe humans don't have the technology to create anything close to a perfect vacuum yet, but does this necessarily mean that a container cannot be completely emptied of any and all atoms? Or maybe the definition of vacuum doesn't stop there at atoms? Energy could be considered too possibly?
     
    Last edited by a moderator: Apr 24, 2017
  5. May 25, 2009 #4

    Mapes

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    Re: Vacuums

    It really is impossible in practice, at least over long time scales. All materials have a vapor pressure; that is, atoms detach all the time. (The vapor pressure increases exponentially with temperature; if it reaches atmospheric pressure, the solid will sublimate to gas even in a closed container.) So it's not possible to have a container-enclosed pure vacuum indefinitely, at least. The time scale depends on the enclosed area, the container material, and the temperature.

    (This doesn't consider the fact that the vacuum would also be immediately filled with photons.)
     
  6. May 25, 2009 #5

    Andy Resnick

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    Re: Vacuums

    There needs to be some additional context to understand what is meant by 'true vacuum'. Torricelli really irked the Pope in the 17th century with his column, and some cosmological models claim the universe is in a false vacuum state.

    Those two uses of the term 'vacuum' are tenuously connected- can you provide additional context?
     
  7. May 25, 2009 #6

    Mentallic

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    Re: Vacuums

    This is what I was looking for. Ok so it's not possible, even for the materials with the highest Boiling Points to stay in a solid state with such low pressures? If space is nearly a vacuum then, why aren't the meteors etc. subliminating? (or are they? comets throw vast gaseous tails behind them).

    Actually I wasn't completely sure about what pure vacuum meant either. I'm thinking of a macroscopic volume of space - such as in a container - being completely emptied of atoms, and possibly energy too.
     
  8. May 25, 2009 #7

    mgb_phys

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    Re: Vacuums

    From an engineering point of view you can't make a perfect vacuum, because even if you made a perfect pump molecules would boil off the surface of the walls. The best laboratory vacuums are about 1million-billion atoms/m^3 , even in deep space there is an atom every few m^3,

    From a cosmological point of view you can't have a perfect vacuum because even in a completely empty universe it is possible for pairs of particles/anti-particles to appear form nothing. This is called a quantum vacuum.
     
  9. May 25, 2009 #8

    Mentallic

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    Re: Vacuums

    Interesting. Is it possible to avoid having these molecules boil off the walls? Maybe freezing the container as well to counteract this boiling? Maybe a perfect vacuum is the same idea as trying to reach absolute zero?

    While a million-billion atoms /m3 is an excellent vacuum in terms of percentage of atoms to that at standard atmospheric pressure, it still sounds like they have failed in creating any sort of decent vacuum :tongue2:
    In the engineering side of things, what is hindering scientists from creating better vacuums?

    I think I might read up on this quantum vacuum to avoid anymore headaches in here.
     
  10. May 26, 2009 #9

    mgb_phys

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    Re: Vacuums

    First limit is the pump technology.
    Imagine a displacement pump (like a bike pump) you open a valve and the pressure equalises inside the vacuum and the pump body, you then close the valve and squeeze that volume down until it reaches atmospheric pressure and spray out the captured molecules to the air. This only works down to the point where the number of molecules left in the pump when you go back to the vacuum is equal to the number coming in from the vacuum, for rotary pumps this is about 1/000 mBar

    Then you switch to turbo pumps, these have angled blades running at very high speed. When an atom drifts up to them it gets hit by the blades and thrown toward the other end of the chamber (where another pump removes it) ultimately when the vacuum gets very low the chance of an atom hitting a blade gets too low and just as many atoms drift back from the collection side as get pushed toward it. About 1/millionth of a mBar or 10^-9 atmospheres.

    Then you use cryopumps. You take a material with a very large surface area like activated charcoal or ceramic pellets and cool them to liquid Nitrogen and then liquid Helium temperatures. Any molecule hitting this surface loses it's energy and sticks.
    This can't pump huge volumes of gas because the surface of the material (called a getter) will fill up but it does give you very high vacuums.
    But ultimately there is a small chance of an atom or molecule having enough energy to boil off the surface, even at absolute zero molecules don't actualy have zero energy.

    The main need for very high vacuums is in particle accelators, so achieving a vacuum of 10^-12 of an atmosphere in a pipe 30mi long is quite good. Especially when a single pin head sized drop of water or oil, or even the grease from a finger print, left inside would mean that you would have a vacuum a million times worse.

    ps. Yes getting ultra high vac even in a small cryostat for say a camera is a very long and tedious job, especially when it takes 2 days to pump and cool the chamber to discover a problem and a day to warm it up again.
     
  11. May 27, 2009 #10

    Mentallic

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    Re: Vacuums

    They all sounds like very ingenious ideas (I thought the best out there was just a more advanced version of the bike pump). I have a few ideas myself, but I'm sure there would be flaws with it since it hasn't already been considered an option. Would there be anything wrong with taking an unsealed container into space, then letting it loose into the void and finally sealing it up before bringing it back to Earth?
     
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