# Is there a limit to a Vacuum?

1. Feb 27, 2006

### pallidin

Greetings, and please forgive my ignorance on the question.

What I am trying to understand is if there is some qualitative limit on producing a "perfect" vacuum.
In other words, let's say that I am in deep space and that I have a vacuum producing piston(by moving the piston away from the "end plate" in a sealed tube, with the other end open of course)
If my piston tube were 20-foot long, I suppose I could do that.
But what if my piston tube were 100-ft long, or 1,000 miles long, or 1,000,000 miles long. Is there a limit?

Thanks

Last edited: Feb 27, 2006
2. Feb 27, 2006

### Homer Simpson

Im guessing that if you did this in a theoretical perfect vaccuum, ie. 0 kPa(a) that the piston would move freely. Since there would be no differential pressure (0 kPa on both sides) it would not be held back by any extra vaccuum.

3. Feb 27, 2006

### pallidin

Ok, so, does the quality or potential characteristics of such an ultra-vaccum differ from that of a standard "perfect vacuum" ?
Or, am I simply "extending" the region of the "perfect vacuum" ?

4. Feb 27, 2006

### ZapperZ

Staff Emeritus
I'm not sure if you're asking this in the ideal sense or in the practical sense. Remember that in the practical sense, your "piston" will be outgassing like mad. So your "vacuum" isn't a vacuum. This is why we have to continue pumping on any vacuum system to maintain the very high vacuum, even when you have a perfect seal - the outgassing rate of the material does matter.

Zz.

5. Feb 27, 2006

### Homer Simpson

Well, I don't think you can really ever get to a 'perfect' vacuum. That would be a volume without any particles of matter at all. There are some good reasons out there on the web explaining why this is not quite achievable. In fact, from what I read it seems more likely that the tube would emit photons and other trapped gasses and likely wind up tending to help push the piston out if in deep space.

6. Feb 27, 2006

### pallidin

Indeed, I failed to take into account the "outgassing" effect of flexible seals, which I would assume can render the seals somewhat "ineffective" under certain vacuum extremes due to actual material loss from the seals(the outgassing) and reduced flexibilty to maintain the seal.

7. Feb 27, 2006

### turbo

Quantum theory tells us (and various demonstrations of the Casimir effect have borne this out) that there is no possibility of producing a perfect vacuum in our Universe. Even in a "perfect" vacuum at 0K virtual particle pairs pop in and out of existence continuously. The calculated density of this vacuum (IIR) is about 1096 Kg/m3.

8. Feb 27, 2006

### ZapperZ

Staff Emeritus
Outgassing isn't just a property of flexible seals. It's a property of practically all material. The stainless steel chamber that is used in many UHV system outgasses all the time, even after a bakeout. Polymers are even worse, and that's why such things are never used in UHV systems.

Zz.

9. Feb 27, 2006

### pallidin

Thanks to everyone in helping me understand this.
I can see that there are specific concerns with respect to UHV(Ultra-high vacuum) systems which must be recognized and/or continuosly addressed in an effective or manageable way.

10. Feb 28, 2006

### Astronuc

Staff Emeritus
Basically one would have to cool a material to near absolute zero to ensure no atoms are outgassed in an UHV.

In practicality, even in space where there are a few atoms per cc, there are nevertheless still atoms.

11. Mar 3, 2006

### Intuitive

What about cooling to near absolute Zero along with a Super conductive induced Magnetic Field pulling or pushing all matter away from a region
to create a Vacuum?

Super intense Magnetic Field.

It seems that just the Super Magnetic Field could do it by iteslf without cooling if the Field is strong enough.
Do you see any draw backs beside the energy requirement?

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Last edited: Mar 3, 2006
12. Mar 3, 2006

### ZapperZ

Staff Emeritus
Er... how do you propose the magnetic field to do this on the neutral outgas?

Zz.

13. Mar 4, 2006

### Intuitive

I thought all http://en.wikipedia.org/wiki/Gases" [Broken], attractive or repulsive force for Atomic Particles not in reference to the Sub Nuclear World?

Are there Atomic Gases not influenced by Super Magnetic Fields, If so, which Gases, This will help me conduct some more research for Nuclear Magnetic Vacuums, using Nuclear Energy to produce Super Mega Magnetic Fields to Condense Matter to a Vaccumed State for my https://www.physicsforums.com/showthread.php?t=91173".

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Last edited by a moderator: May 2, 2017