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B If you had to make a perfect vacuum, version #2

  1. Jan 5, 2017 #1
    I posted this question again in a different way, but it was a mess, and people were not satisfied, so it was closed down. I hope this time it's ok.

    Let's say humanity could concentrate all of its resources to create a perfect vacuum (neutrinos, photons etc don't count, it only has to be devoid of any atoms). The vacuum chamber doesn't have to be that large, 1cm^3 will do. Is it possible to create this sort of vacuum and maintain it for an extended period of time with current technology, but all the resources available to humanity and not considering time and economical cost? If yes, how?
     
  2. jcsd
  3. Jan 5, 2017 #2

    anorlunda

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    Even if you succeeded in making a perfect vacuum, atoms would come off the walls of the container spoiling it. So your question must be changed to a perfect vacuum with no walls, no container. What do you think the answer is?
     
  4. Jan 5, 2017 #3
    Are you talking about the walls outgassing or air diffusing through them?
     
  5. Jan 5, 2017 #4

    Vanadium 50

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    You had outgassing in your last thread, you still have it now. And you'll have it again if you ask a third time.
     
  6. Jan 5, 2017 #5
    I agree. I'm just asking if it's possible to eliminate it somehow and how you'd do that if you could.
     
  7. Jan 5, 2017 #6

    sophiecentaur

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    You would need to specify what you mean by 'nothing' and the size of the region that you are dealing with. Go into the deepest space and they tell us that you find about 1 proton per metre cube. So you would have a pretty good chance of finding 'no protons' (H atoms) in a randomly chosen 10cm cube.
    Unfortunately you have no chance of putting that in a bottle and bringing it home and, even as you reached out for it, you would be introducing all sorts of atoms from your bottle.
    Questions involving 'Zero' of anything tend to get us nowhere. They are about as meaningful as questions about battles between Superman and Batman.
     
  8. Jan 5, 2017 #7

    ZapperZ

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    The lowest pressure that I've ever created was 10-11 Torr with a combination of 2 ion pumps. I believe, right now, one can get down to maybe 10-12 Torr with combinations of ion and cryopumps, and maybe add a few cold fingers here and there.

    I don't know of any macroscopic volume that has "zero" pressure or "perfect" vacuum. What is that? Even under ultra-high vacuum, if you look at the RGA signal, you'll always see hydrogen species.

    But as someone who always had to worry about cost-versus-benefit, the question that pops up into my head here is "Why is this important?". Why would one need to know or make something like this? The mean-free path of collision is already waaaay larger than the size of the vessel, so there is no effect from scattering, if that is a concern. So why would one want an even better vacuum? Does one have a hypersensitive surface exposure problem? I deal with that all the time (ref: antimonide photocathodes), and even there, the gas specie that bombards the surface makes a lot of difference, not just the vacuum level.

    This is one of those situations that separate the scientists from the non-scientist: It may be interesting, but is it important?

    Zz.
     
  9. Jan 5, 2017 #8
    Of course not!

    Yes, apparently the closest thing to a perfect vacuum created is something like 100 atoms per cubic centimeter.
     
  10. Jan 5, 2017 #9
    Well, I did specify it: no atoms of any sort in a volume of about 1 cubic centimeter. Honestly I did not think of going off into space and enclosing an area, but that is still a bit problematic.

    Is it possible to completely prevent outgassing or remove all gas particles from a given space? Furthermore, can you completely stop diffusion through the walls of the chamber?
     
  11. Jan 5, 2017 #10
    Are ion pumps and cryopumps able to reach higher vacuums than turbomolecular pumps?
     
  12. Jan 5, 2017 #11

    nsaspook

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    Ion pumps are but large cryopumps are usually installed in process chambers because of their massive flow rates for trapping generated by-products like water vapor or light molecules instead of the ultimate vacuum level.

    https://www.duniway.com/images/_pg/ion-pumps-operation-applications.pdf
     
  13. Jan 5, 2017 #12

    Vanadium 50

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    No, no, a thousand times no. No matter how often you ask it.
     
  14. Jan 5, 2017 #13
    Ok, ok, no need to be so aggressive. Which part is more problematic, outgassing or getting particles put of there? Or are they both equally problematic?
     
  15. Jan 5, 2017 #14
    Every material we know of evaporates, albeit some very slowly. But any 1 cc container made of any known material would, at equilibrium, have way more evaporated atoms or molecules in it than you would be happy with.
     
  16. Jan 5, 2017 #15
    Oh snap, I was looking forward to creating a true vacuum to perform our little pasta experiment ;)

    Do all materials evaporate even when kept at really low temperatures? I did not know that...
     
  17. Jan 5, 2017 #16
    The vapor pressure of solid iron below its melting point, in Pa, is given by the equation

    log (P/Pa) = 12.106 - 21723 / (T/K) + 0.4536 log (T/K) - 0.5846 (T/K)−3

    where the temperature is in degrees K.
     
  18. Jan 5, 2017 #17

    sophiecentaur

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    There is every reason to criticise the question, even when only asked once. It is not Science. A question that asks what are the limiting factors in producing a very low vacuum would elicit some much more constructive answers cos that's yer actual Science.
     
  19. Jan 5, 2017 #18
    That's true, but I see the original question as more of a way to initiate discussion. For example, someone mentions outgassing, good, let's talk about outgassing. The scenario is completely hypothetical, and not very useful, so the discussion is much more constructive than the actual answer to the question. Maybe asking the question you proposed would be better at achieving that, but asking that question doesn't really touch on the methods that could potentially be used to push on the limitations.
     
  20. Jan 5, 2017 #19

    sophiecentaur

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    Perhaps you could judge things in terms of some of the responses you've been getting. Pull the right levers for the result you need. Try it.
     
  21. Jan 5, 2017 #20
    So you need something more than simply a box to contain a very good vacuum. Obviously, you need to keep the walls cold to limit outgasing. I think it might be possible to "blow away" atoms with a laser field in the cavity, but you need to deal with the laser hitting the walls and heating them up. Some kind of changing magnetic field might be used to guide particles out of the cavity. I'm sure with the full brainpower of humanity working on it, we could achieve several orders of magnitude lower pressures than what is currently possible.
     
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