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

[Andreas C]

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?

 

[anorlunda]

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?

 

[Andreas C]

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?

Are you talking about the walls outgassing or air diffusing through them?

 

[Vanadium 50]

You had outgassing in your last thread, you still have it now. And you'll have it again if you ask a third time.

 

[Andreas C]

You had outgassing in your last thread, you still have it now. And you'll have it again if you ask a third time.

I agree. I'm just asking if it's possible to eliminate it somehow and how you'd do that if you could.

 

[sophiecentaur]

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?

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.

 

[ZapperZ]

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.

 

[Andreas C]

It may be interesting, but is it important?

Of course not!

I don't know of any macroscopic volume that has "zero" pressure or "perfect" vacuum.

Yes, apparently the closest thing to a perfect vacuum created is something like 100 atoms per cubic centimeter.

 

[Andreas C]

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.

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?

 

[Andreas C]

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.

Are ion pumps and cryopumps able to reach higher vacuums than turbomolecular pumps?

 

[nsaspook]

Are ion pumps and cryopumps able to reach higher vacuums than turbomolecular pumps?

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

 

[Vanadium 50]

Is it possible to completely prevent outgassing or remove all gas particles from a given space?

No, no, a thousand times no. No matter how often you ask it.

 

[Andreas C]

No, no, a thousand times no. No matter how often you ask it.

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?

 

[Chestermiller]

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?

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.

 

[Andreas C]

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.

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...

 

[Chestermiller]

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...

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.

 

[sophiecentaur]

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?

There is every reason to criticize 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.

 

[Andreas C]

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.

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.

 

[sophiecentaur]

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.

 

[Khashishi]

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.

 

[Andreas C]

Perhaps you could judge things in terms of some of the responses you've been getting.

I just learned something new and useful by chestermiller, that's good enough for me.

 

[Andreas C]

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.

Have those mechanisms been used in a real experiment? Could you provide an example? Honestly I don't know much at all about the subject, and it's the first time I hear about them.

 

[Chestermiller]

I just learned something new and useful by chestermiller, that's good enough for me.

Actually, I used the equation to calculate the actual density of iron vapor in equilibrium with solid iron. At 600 K, it came out to only 95 atoms per cubic meter. So evaporation of the container walls would not be a problem. Release of adsorbed gases would have to be considered.

 

[Andreas C]

At 600 K, it came out to only 95 atoms per cubic meter. So evaporation of the container walls would not be a problem.

That's good to know!

. Release of adsorbed gases would have to be considered.

That's... Well, it's still good to know, but it's not helping our hypothetical (lost) cause.

There are various methods to remove absorbed gases from the materials of the container, but I'm not sure how effective they are when you have to deal with this sort of stuff.

I have a dumb question: in the case of the mercury barometer, an obvious issue is the mercury vapour. Is it possible to freeze the mercury fast enough to sort of prevent that from happening? Actually, scrap mercury. Galium is also liquid at relatively low temperatures, and it doesn't evaporate as much. It's probably a silly question, but I'm interested in the answer.

 

[jbriggs444]

I have a dumb question: in the case of the mercury barometer, an obvious issue is the mercury vapour. Is it possible to freeze the mercury fast enough to sort of prevent that from happening? Actually, scrap mercury. Galium is also liquid at relatively low temperatures, and it doesn't evaporate as much. It's probably a silly question, but I'm interested in the answer.

What is the question and why are you asking in this thread?

 

[Andreas C]

What is the question and why are you asking in this thread?

Someone mentioned in "version 1" of this thread the "vacuum" in mercury barometers, which was problematic for many reasons, including the mercury evaporating. I'm wondering if it could be possible to significantly retard the process by cooling it really fast.

 

[PAllen]

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...

You don't need any high vacuum for the pasta experiment, just pressure difference. And that can be made as large as you want by having the exterior be above 1 atmosphere.

 

[Andreas C]

You don't need any high vacuum for the pasta experiment, just pressure difference. And that can be made as large as you want by having the exterior be above 1 atmosphere.

I know, it was just a stupid joke.

 

[sophiecentaur]

including the mercury evaporating.

You really do need to get practical with this. There is always 'some pressure' in any region and we just have to live with it. As long as it is kept to a level that doesn't affect the process that's being studied (acceptable error) then it can be ignored. Otoh, it is sometimes significant but measurable and can be included as a factor.
You may as well asking how can a massless beam be constructed for a building structure or a perfect battery made for an electrical experiment. Other nonsense scenarios are traveling at the speed of light and achieving absolute zero temperature. And Perpetual Motion is another one; PF explicitly bans that topic.

 

[Andreas C]

You may as well asking how can a massless beam be constructed for a building structure or a perfect battery made for an electrical experiment. Other nonsense scenarios are traveling at the speed of light and achieving absolute zero temperature. And Perpetual Motion is another one; PF explicitly bans that topic.

Some of those are also theoretically impossible, a perfect vacuum isn't.

 

[sophiecentaur]

Some of those are also theoretically impossible, a perfect vacuum isn't.

Of course it is.

 

[Andreas C]

Of course it is.

Theoretically impossible? No, there are tons of it everywhere.

 

[sophiecentaur]

Theoretically impossible? No, there are tons of it everywhere.

Tons? = Mass = vacuum??
But how would you define your perfect vacuum? How big a volume and for how long would you have to have your vacuum exist? The only way you could actually check that it's there would be to measure the presence of atoms and your atom detector could have missed that final atom in the time (however long) taken for the experiment.
I'm sorry but it is really a nonsense. It's not Science. If you cannot measure something then you cannot say it exists.
You are dealing with statistics here and there is never a zero probability of finding an atom in a given region; it's just very low down on the skirts of a probability distribution. The more money you spend, the lower down you can go but that's still not zero.
Specify some particular conditions and you can get a sensible answer (albeit very ball park).

 

[Andreas C]

Tons? = Mass = vacuum??

It's a 'joke", an expression, don't take it literally.

But how would you define your perfect vacuum? How big a volume and for how long would you have to have your vacuum exist?

Well, someone mentioned deep space. Out there you'd find less than an atom per cc. I'm not sure exactly how many there are in interstellar space, because sources seem to say from 1 atom per cubic meter to 1 atom per cc. Theoretically you can use something to keep atoms away for a while, or you can pick a smaller volume, and you should definitely be able to keep your "perfect vacuum" intact for some time. Apparently the average density of the universe is 5.9 atoms per cubic meter, so it's pretty vacant at many points.

The only way you could actually check that it's there would be to measure the presence of atoms and your atom detector could have missed that final atom in the time (however long) taken for the experiment.

Again, this is all hypothetical. Let's assume you had a perfect detector, or that you could leave it in there for very long.

Specify some particular conditions and you can get a sensible answer (albeit very ball park).

Alright then. How about getting less than 10 atoms per cc? Is that better? Less than 10 is practically nothing.

 

[sophiecentaur]

It's a 'joke",

Mine too.

Alright then. How about getting less than 10 atoms per cc? Is that better?

MUCH better. That takes us from nonsense to almost sense. Except for the 'perfect detector' and the 'very long'. In some fields of study, 'very long' could be 1ns.

Less than 10 is practically nothing.

Haha. You would need to talk to a Mathematician about that statement and it's all relative. But you are now talking in the terms that can actually get an answer.
I remember my boss once picked me up for using the word "several". He replied "do you mean Eleveral?" It gave me a 'thing' about being quantitative when I can be.

Further to the 'pasta' problem. 'Suck' is a funny quantity. You get virtually the same amount of Suck with a cheap and cheerful vacuum pump and a state of the art one because AP minus a small number is much the same as AP minus a really small number - for the purposes of sphagetti and general engineering. Otoh, a force pump (positive) pressure can make a serious difference to the situation.

 

[Andreas C]

Mine too

...oh... I feel a bit awkward now...

That takes us from nonsense to almost sense. Except for the 'perfect detector' and the 'very long'. In some fields of study, 'very long' could be 1ns.

Let's assume we have a detector that can always detect an atom if it's there, and does not cause issues like polluting it with more atoms. And let's call "very long" something "easy" at first, 100 seconds.

Haha. You would need to talk to a Mathematician about that statement and it's all relative

It's all relative, and that's why I said less than 10 is practically nothing. As you said, it's possible to not even detect it without our perfect detector.

AP minus a small number is much the same as AP minus a really small number

Are you asking me to leave things to chance like that? I've sent the noodle to a lab to remove imperfections to a molecular level! Do you think this is a game?

Anyway, if I get to try the experiment I'll just use a vacuum cleaner. Right now the "vacuum" is the least of the issues.

 

[jbriggs444]

Do you think this is a game?

Of course it is. None of this has any practical application.

 

[Andreas C]

Of course it is. None of this has any practical application.

Are you telling me that performing an experiment involving sucking noodles with the utmost precision has no practical application? What are you going to say next, that it's useless to think of how many angels can dance on the head of a pin?

 

[jbriggs444]

Are you telling me that performing an experiment involving sucking noodles with the utmost precision has no practical application? What are you going to say next, that it's useless to think of how many angels can dance on the head of a pin?

This is the vacuum thread, not the sucking noodle thread. That thread is much more than a game.

 

[Andreas C]

This is the vacuum thread, not the sucking noodle thread. That thread is much more than a game.

Yes, it's very interesting. I just joked about using a perfect vacuum to test a model that was proposed there.

 

[mfb]

Yes it is possible to fully evacuate a 1 cm³ volume.

The BASE experiment at CERN made a vacuum so good that they couldn't detect any remaining gas, and set an upper limit of 3 particles per cm³. Even if the density is at the upper limit (it is expected to be at least 1-2 orders of magnitude better), based on Poisson statistics, cubic-centimer-sized regions free of atoms occur all the time. Or, put differently, if their trap would be smaller there would be a reasonable chance to have 0 atoms in it.

The BASE experiment had antiprotons in their vacuum, they are not included in the particle number estimate of course. Those antiprotons were stored in the vacuum for more than a year without detectable annihilation.

The trick to prevent outgassing is the temperature: the whole vacuum chamber is cooled to 6 K. At that energy the atoms stay trapped in and at the walls. Even helium atoms stay attached to the walls as long as there is not enough helium to form a full layer.

 

[Andreas C]

The BASE experiment at CERN made a vacuum so good that they couldn't detect any remaining gas, and set an upper limit of 3 particles per cm3. Even if the density is at the upper limit, based on Poisson statistics, cubic-centimer-sized regions free of atoms occur all the time. Or, put differently, if their trap would be smaller there would be a reasonable chance to have 0 atoms in it.

That's amazing! How long was this maintained?

So that sorts outgassing. How did they manage to evacuate the chamber so well?

 

[mfb]

That's amazing! How long was this maintained?

Well, at least a year, that's how long the antiprotons were in it.

How did they manage to evacuate the chamber so well?

Same approach: Cooling. Start with a very good vacuum, then seal the chamber completely, then cool it. All the remaining atoms freeze out at the walls.

Longer explanation: BASE publication, page 24. The reference given there has a detailed description:
Thompson, W. (1977). "Characteristics of a cryogenic extreme high-vacuum chamber". Journal of Vacuum Science and Technology. 14 (1): 643–645. Bibcode:1977JVST...14..643T. doi:10.1116/1.569168.

 

[Vanadium 50]

nd set an upper limit of 3 particles per cm3. Even if the density is at the upper limit (it is expected to be at least 1-2 orders of magnitude better),

Where do you see this? I see 10^-14 mbar as the limit of measuring. That's about 500 particles/cm³. Ref. [17] would be nice to look at, if it were complete or pointed at a preprint. From their proposal, they thought they could do ~50x better than this, so we're still an order of magnitude away. Even your 3 is not 1.

There are some complications. We're interested in density, and typically what is reported is a pressure. At very low densities, especially with cryogenics, you don't have thermal equilibrium and so pressure becomes a less and less good proxy for density. The other is that, because you are out of equilibrium, the density varies throughout the volume. The BASE design (and the LHC vacuum pipe design) takes advantage of this and has a lower-than-average density where the beam or target is. I think that's cheating: it is almost certain that there is a cubic centimeter of the LHC without any gas molecules. I just can't tell you which cubic centimeter it is.

 

[Andreas C]

Ref. [17] would be nice to look at, if it were complete or pointed at a preprint.

I'm not sure if it is what you're looking for, but it seems to refer to p. 24 of this: http://cds.cern.ch/record/2120817/files/SPSC-SR-177.pdf

It just mentions that the storage time is more than 1.08 years.

 

[mfb]

nd set an upper limit of 3 particles per cm3. Even if the density is at the upper limit (it is expected to be at least 1-2 orders of magnitude better),

Where do you see this?

See the first link (post 41):

“Given that we have not observed any antiproton disappearance yet,” says Christian Smorra, a research fellow on the BASE collaboration, “we can say that there are less than three matter particles left per cubic centimetre.”

3 is not 1 and not 0 either, but see above: Poisson statistics.

I'm not sure if it is what you're looking for, but it seems to refer to p. 24 of this: http://cds.cern.ch/record/2120817/files/SPSC-SR-177.pdf

It just mentions that the storage time is more than 1.08 years.

That is based on 3 months, they have more than a year now.

 

[Andreas C]

That is based on 3 months, they have more than a year now.

Oh good! I certainly did not expect a vacuum so close to perfect to have already been obtained, that really changed my perspective.

 

[OmCheeto]

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.

Interesting. I'm guessing this is why: "When astronauts return from space walks and remove their helmets, they are welcomed back with a peculiar smell. An odor that is distinct and weird: something, astronauts have described it, like "seared steak." And also: "hot metal." And also: "welding fumes."" [ref]

ps. Sorry to be so late to the thread, but I just saw it today, and I'd just heard about space smelling like metal a couple of months ago, and a hypothesis regarding the evaporation of metal was the first thing that popped into my mind.
Thank you CM!

 

[256bits]

3 is not 1 and not 0 either, but see above: Poisson statistics.

There is some more going on than just the particle density, such as mean free path and how long before an expected collision.
For intergalactic space, isn't an expected collision mean free path measured in light years.
For atmospheric air, in mm.
For an ultra high vacuum, in kilometres.
Cool the gas temperature down lowers the velocity of the particles, and the expected time between collisions should increase.

 

[256bits]

Interesting. I'm guessing this is why: "When astronauts return from space walks and remove their helmets, they are welcomed back with a peculiar smell. An odor that is distinct and weird: something, astronauts have described it, like "seared steak." And also: "hot metal." And also: "welding fumes."" [ref]

ps. Sorry to be so late to the thread, but I just saw it today, and I'd just heard about space smelling like metal a couple of months ago, and a hypothesis regarding the evaporation of metal was the first thing that popped into my mind.
Thank you CM!

Or cosmic rays encountering the metal/