Define a real Vacuum?

[rigney]

I've asked the question several times, but finding no solid answers other than innuendo, I keep searching. Even NASA wants $15. for a supposed qualified answer. And that's only a maybe! If I may, I'll ask it one more time of you guys.

 

A spherical cylinder is vacuumed to -30” of mercury and taken into intergalactic space. There the vacuum on the container continues to be increased. At some point will the capsule collapse, (implode)? Honest injun now! No hypotheticals, just hard facts. I'll look at almost any link you offer, if I can find anything substantial. I just can't seem to find it on my own.

[JustinW]

I'm looking for an actual deffinitive answer because you've got me curious. I ran across this in doing so. It doesn't answer the question but is really cool anyway.

 

[rigney]

I'm looking for an actual deffinitive answer because you've got me curious. I ran across this in doing so. It doesn't answer the question but is really cool anyway.

 

Thanks guy! I appreciate your input and curiosity. I hadn't seen this video and it is not exactly what I'm looking for either, but it is a start. I believe my question is within reason, it's just that I cant find a plausible answer to it. You find anything, give me a buzz. I'm sure someone on the forum has an ironclad answer. Edited February 15, 2012 by rigney

[DrRocket]

I've asked the question several times, but finding no solid answers other than innuendo, I keep searching. Even NASA wants $15. for a supposed qualified answer. And that's only a maybe! If I may, I'll ask it one more time of you guys.

 

A spherical cylinder is vacuumed to -30" of mercury and taken into intergalactic space. There the vacuum on the container continues to be increased. At some point will the capsule collapse, (implode)? Honest injun now! No hypotheticals, just hard facts. I'll look at almost any link you offer, if I can find anything substantial. I just can't seem to find it on my own.

 

No.

 

Implosion of a structure like a cylinder is a function of the applied load on the boundary -- in this case the differential pressure between the interior and exterior. If it did not implode on Earth it will not implode in space. In fact the differential pressure in space vs on Earth will be both lower in magnitude and differ in sign and this will be reflected in the stress state of the cylinder. On Earth the cylinder will be in compression as the outside pressure is greater than the inside pressure, while in space the reverse will be true initially and in any realistic situation (laboratory vacuums are not as complete as the vacuum of space). So in space the skin of the cylinder will be in a state of slight tension. Cylinders more easily survive an internal pressue load than an external crushing load.

 

Now, even in the idealized situation in which one might achieve a more complete vacuum inside the cylinder than that of space, the net pressure difference will be nearly 0 -- the difference between two very small pressures -- and the stress will be extremely low. The cylinder will have survived a much more severe stress state on Earth.

[JustinW]

Yeah I've asked similar questions about vacuum before and haven't gotten too many results. I think the fact of the matter is that we don't know too much about the vacuum of space. The closest solution I could come up with would be one of two things.

 

1- If the vacuum pressure in the cannister was strong enough to exceed the structural integrity of the cannister, it would inturn cause the cannister to collapse.

2- For that to happen you would have to assume that the pressure inside the cannister would have to greatly exceed the pressure on the outside of the cannister in order for it to collapse.

 

All this is speculative on my part though with me being the ameteur that I am. I have thought about this question before though, wondering if it is the pressure inside the cannister that allows it to collapse. Or if it is the outside pressure that forces the collapse once the vacuum inside crosses the threshold of the container's limits.

 

Rocket, I must have been writing while you posted. That makes sense.

Edited February 15, 2012 by JustinW

[rigney]

No.

 

Implosion of a structure like a cylinder is a function of the applied load on the boundary -- in this case the differential pressure between the interior and exterior. If it did not implode on Earth it will not implode in space. In fact the differential pressure in space vs on Earth will be both lower in magnitude and differ in sign and this will be reflected in the stress state of the cylinder. On Earth the cylinder will be in compression as the outside pressure is greater than the inside pressure, while in space the reverse will be true initially and in any realistic situation (laboratory vacuums are not as complete as the vacuum of space). So in space the skin of the cylinder will be in a state of slight tension. Cylinders more easily survive an internal pressue load than an external crushing load.

 

Now, even in the idealized situation in which one might achieve a more complete vacuum inside the cylinder than that of space, the net pressure difference will be nearly 0 -- the difference between two very small pressures -- and the stress will be extremely low. The cylinder will have survived a much more severe stress state on Earth.

I appreciae your expertise and reply, but what I'm looking for are cold hard facts. Has there been any qualified experiments to validate my question, one way or another? If you can supply a link as to where these tests were conducted conclusively, I will believe. Otherwise, it's nothing more than theory.

[StringJunky]

I appreciae your expertise and reply, but what I'm looking for are cold hard facts. Has there been any qualified experiments to validate my question, one way or another? If you can supply a link as to where these tests were conducted conclusively, I will believe. Otherwise, it's nothing more than theory.

 

If we assume there are zero atoms in your container, which I think your -30mmHg figure implies, and there are only one, or even a few hundred molecules, per cubic metre as in intergalactic space, the pressure differential is negligible. Pressure, in this scenario, is the rate at which atoms or molecules impact on a surface.

 

Dr Rocket gave you a great explanation and doesn't need proving...logic and little bit of thought is enough. Maybe DrR could tell you the number of atoms per unit space required to make a measurable difference between the inside and outside of the vessel.

Edited February 15, 2012 by StringJunky

[rigney]

If we assume there are zero atoms in your container, which I think your -30mmHg figure implies, and there are only one, or even a few hundred molecules, per cubic metre as in intergalactic space, the pressure differential is negligible. Pressure, in this scenario, is the rate at which atoms or molecules impact on a surface.

 

Dr Rocket gave you a great explanation and doesn't need proving...logic and little bit of thought is enough. Maybe DrR could tell you the number of atoms per unit space required to make a measurable difference between the inside and outside of the vessel.

Quote]Quite honestly I wasn't looking for explinations. I merely asked if there was a link that would conclude this theory as fact? In a word, have we tried such experiments in space?

Edited February 15, 2012 by rigney

[mississippichem]

An experiment is not necessary. This is VERY established physics.

[rigney]

An experiment is not necessary. This is VERY established physics.

You don't say!

[StringJunky]

Quite honestly I wasn't looking for explinations. I merely asked if there was a link that would conclude this theory as fact? In a word, have we tried such experiments in space?

There has been no space mission that has entered intergalactic space so the answer will be no. Voyager 1 is the furthest (120 AU from Earth) and that hasn't even reached the interstellar medium yet let alone the intergalactic space.

 

http://voyager.jpl.nasa.gov/mission/

[D H]

A spherical cylinder is vacuumed to -30” of mercury

By -30” of mercury you mean pressure relative to one standard atmosphere. Note that a standard atmosphere at freezing is 29.92 inches of mercury. There is no such thing as absolute negative pressure. Your -30” of mercury doesn't quite make sense. BTW, measuring pressure in inches of mercury is an old and outdated concept.

 

and taken into intergalactic space. There the vacuum on the container continues to be increased. At some point will the capsule collapse, (implode)?

You also have a very confused notion of the capabilities of our space programs. You have an even more confused notion of the concept of vacuum. Rather than repeat what DrRocket already said just in this thread, or repeat what many of us have said over and over, in other threads, read those posts.

[rigney]

There has been no space mission that has entered intergalactic space so the answer will be no. Voyager 1 is the furthest (120 AU from Earth) and that hasn't even reached the interstellar medium yet let alone the intergalactic space.

 

http://voyager.jpl.nasa.gov/mission/

Thanks for correcting my rrror. "Outer space" would have done just fine. Strange that you were the only one to pick up my mistake. While I will never be a physicist, I do understand the difference between vacuum and pressure, but just looking for answers.

[Moontanman]

Rigney, you can't pump anything to an absolute negative pressure, just like there is no temp below absolute zero. You cannot pump the vacuum out of anything, it genuinely doesn't make sense... I understand that you are asking what is a vacuum and i think it's a viable question but you can't pump out the vacuum, at least not in the context of modern physics.

 

The question of what is the vacuum is a reasonable question, a recent article in Discover magazine show casing the works of Julian Barbour has some interesting ideas about Space and what it is. He is trying to overturn Einstein, his ideas are interesting but way beyond me mathematically but the concepts are not impossible to grasp. If I understand them correctly he doesn't even think the concept of space time is correct, no 4th dimension and space is just ... space...

 

http://platonia.com/papers.html

[rigney]

Rigney, you can't pump anything to an absolute negative pressure, just like there is no temp below absolute zero. You cannot pump the vacuum out of anything, it genuinely doesn't make sense... I understand that you are asking what is a vacuum and i think it's a viable question but you can't pump out the vacuum, at least not in the context of modern physics.

 

The question of what is the vacuum is a reasonable question, a recent article in Discover magazine show casing the works of Julian Barbour has some interesting ideas about Space and what it is. He is trying to overturn Einstein, his ideas are interesting but way beyond me mathematically but the concepts are not impossible to grasp. If I understand them correctly he doesn't even think the concept of space time is correct, no 4th dimension and space is just ... space...

 

http://platonia.com/papers.html

Appreciate your input Moon, and I'm not trying to overthrow Einsteins theories in any sense, since I'll never be that smart. Vacuum though, is only a concept we have reached through the basic interpolation of physics. Yet, understanding what a pure vacuum is, just might explain the singularity that supposedly created our universe. While I'm not an advocate of that principal, it is possible. I'm just looking for honest answers, not a metaphor or assumption. Edited February 16, 2012 by rigney

[rigney]

Thanks for correcting my rrror. "Outer space" would have done just fine. Strange that you were the only one to pick up my mistake. While I will never be a physicist, I do understand the difference between vacuum and pressure, but just looking for answers.

This is a nice video of a cruises set in motion 30+ years ago. Some on the forum wasn't even born when it began, but stranger yet is how quickly many of us tend to forget such importance.

Edited February 16, 2012 by rigney