[PmbPhy (OP)]

What comes to your mind when you hear the term "vacuum"?  The reason I ask is because all too many times when the subject of discussion is classical physics and we're talking about a vacuum there's always someone who brings up the quantum nature of the vacuum. If you're one of those people then I'd like to ask you why you do it? I doubt that most members here are ignorant of the quantum nature of the vacuum so there's no need to bring it up. And it confuses the issues since it's always irrelevant to the subject at hand, i.e. classical mechanics. It requires people to pause the discussion in order to explain to that person that the quantum nature of the vacuum is irrelevant to the subject at hand. Such precision is too small to be worth considering because that's what is meant buy classical mechanics. Thanks.

[Bored chemist]

http://www.henryvacs.co.uk/

[scotty stull]

A vacuum is seen as a lack of something, if we are dealing with a gas and when this gas density is decreased to the extent that the mean free path is much larger than the container, molecules rattle around like the balls on a billiard table ( not a pool table, where the ball density can be high), and gas behavior is determined by the random motion of the molecules as they bounce from wall to wall. Now the question remains what is between the molecules in that vacuum chamber? Also light bends when it passes through molecules and light bends very little when it passes through a vacuum that has very little molecules. What comes to my mind is that there is orbiting particle systems that are much smaller than the molecules that are in this vacuum chamber. The number of these orbiting particle systems increases when more of the molecules are removed from this vacuum chamber! Would these orbiting particle systems be the ones that make up a electron , a electron cloud and or both?

[scotty stull]

What can i say i am sorry... You did ask the question ( what comes to your mind when you here the term "vacuum' ).
I did not say anything about quantum mechanics, nor did i say any thing about classical physics, for me these are tools of the trade and as a mechanic you need more and better tools to better do your job!

[jeffreyH]

What comes to mind?  Absence of any material things. A void. That isn't necessarily what the vacuum is.

[PmbPhy (OP)]

That isn't necessarily what the vacuum is.

Why isn't it?

Question: What about a region of space that contains only static electric and magnetic fields? We'll model this by ignoring everything else. Is that a vacuum to you?

[alancalverd]

Philosophically: a volume containing nothing at all.

Theoretical physics textbook: a space within which a freely-moving particle is more likely to reach the boundary than to collide with any other particle.

A lifetime of experimental physics: a space containing a few air molecules, rather more pump oil molecules, and measurable quantities of solder flux, Boss White sealing compound, an exploded cockroach (in a scanning electron microscope) fingerprint grease, dimethyl ketone, helium, a rusty spanner, and a cheese sandwich. 

Using an oversized turbomolecular pump we eventually managed to pump the linac down to the point where the electron beam left the primary gun and travelled down the static ladder but never reached the target. After a few minutes the pressure crept up and everything went to hell in a handbasket, every day, until we dismantled the whole damn thing and found a cheese sandwich with a neat hole punched through it, right in the centre of the flight tube. The suspect said "It proves that I set the magnetic deflectors up exactly right."

The experiment is repeatable: apparently the LHC suffered exactly the same fault 40 years later. Thus either  bread magically appears in a vacuum (Exodus 16:15) or the Higgs Boson is made of cheese.   

As a footnote I've since had a million dollar MRI system brought to a grinding halt by Boss White residue in the cooling water, which then screwed the vacuum pumps. Spooky action at a distance! The builder denies ever having used the stuff, so perhaps it haunts me.

[Ethos_]

What comes to your mind when you hear the term "vacuum"?

Something far different than the term "perfect vacuum". Even space is not perfectly evacuated having random particles and electro-magnetic fields present. Fact is; There is no space empty of field.

In summation, when I think of the word "vacuum", I think of either space or a failed laboratory attempt at reaching that "perfect vacuum".

[scotty stull]

pmbphy ; To me a static electric field would be a differential pressure field held in place by hole flow and the check valve effect. Also a magnetic field would be a flow of mass, like a permanent magnetic generator operation where motion input produces a flow of electrons, but instead of electrons smaller parts of the electrons produce the magnetic field. Conventional wisdom says this can not happen.

[jeffreyH]

That isn't necessarily what the vacuum is.

Why isn't it?

Question: What about a region of space that contains only static electric and magnetic fields? We'll model this by ignoring everything else. Is that a vacuum to you?

If the fields are static they have a potential but are not doing anything. If no particles are present there will be no effect. This is actually a difficult problem in some respects. Which is why I believe you asked it.

[PmbPhy (OP)]

pmbphy ; To me a static electric field would be a differential pressure field held in place by hole flow and the check valve effect.

Well, if that's what it is to you then that's what it is to you. I can only ask why it's like that to you at this point. What do you mean by a differential pressure field as it pertains to a static electric field? I didn't say what the field was like. It could very well be a uniform static field and as such the differential to such a field is zero since it doesn't change from place to place.

[PmbPhy (OP)]

If the fields are static they have a potential but are not doing anything. If no particles are present there will be no effect. This is actually a difficult problem in some respects. Which is why I believe you asked it.

No. That's not it. Einstein define "matter" as being present in places where the stress-energy-momentum tensor does not vanish. Some physicists still hold to this such as Hans C. Ohanian. To him this is another state of matter. So in a region of space devoid of everything except for electromagnetic fields there is matter in that region. And this is a classical point of view since relativity is a classical theory.

[jeffreyH]

If the fields are static they have a potential but are not doing anything. If no particles are present there will be no effect. This is actually a difficult problem in some respects. Which is why I believe you asked it.

No. That's not it. Einstein define "matter" as being present in places where the stress-energy-momentum tensor does not vanish. Some physicists still hold to this such as Hans C. Ohanian. To him this is another state of matter. So in a region of space devoid of everything except for electromagnetic fields there is matter in that region. And this is a classical point of view since relativity is a classical theory.

That's interesting. Do you have any articles or references?

[Thebox]

Several things come into my mind when I hear the term vacuum.  I consider that there is several aspects of a vacuum but consider the main aspect is space. I consider a vacuum is space that is empty of anything of mass, not to be mistaken for a void that is absent of everything.
To consider space as a vacuum would be hard to imagine with out imagining a confinement of walls, so maybe vacuums are just something we make by confining space and they do not exist in any other context.

[Dreamian]

When I think of a Vacuum, not being a physicist, I simply think of a vessel that has by some means been vacated of that which would stabilize its pressure with that of its surroundings. However, in reference to space, I would then be inclined to look at it as a much larger vessel which was vacated by . . . . Gravity?  I would never think a void as being the same thing as a vacuum, obviously (at least obvious to me), however I do believe that "Void" could well play a part in creating a vast vacuum in space.

[PmbPhy (OP)]

..., I simply think of a vessel that has by some means been vacated of that which would stabilize its pressure with that of its surroundings.

I don't know what "stabilize its pressure with that of its surroundings" means. Can you rephrase it for me please? Why do you think of a vessel when you think of a vacuum?

Typically a region of space that has a vacuum in it is independent of its surroundings. I never mentioned any container of any kind in the opening post (OP).

[Dreamian]

It is just what comes to mind when I think of a vacuum. A vessel could come in the form of a canister that has most of the air pumped from it. We would then consider the canister to contain a vacuum in reference to the canister's surroundings.  I used "stabilize" meaning the pressure within the canister was "stable" (the same as) with the pressure outside the canister. 

We make use of "vacuum breakers" on water lines to stabilize the pressure (get rid of the vacuum) so that water is not siphoned back into the water source. as an example.  The water pipes in this example would be the vessel.