[Bobsey (OP)]

This vacuum hasnt got planets or stars in it like space , I can't understand how space is a vacuum ?

Steve, it's the space between the planets and stars that is a vacuum.

Steve?

The universal volume , isn't a empty set , vector space has particels and comets passing through it all the time , it is never really empty space . It can't be a vacuum when it isn't devode of all matter .

You all explained a vaccum is devode of all matter , space , the universe , is't devode of all matter .

I ca't understand why you cosider space is a vacuum when it isn't devode of mattter .

[alancalverd]

I say again: space is a vacuum. The universe is mostly space, plus some matter. Do not confuse "universe" and "space"- this is a science forum, not a bunch of bad journalists torturing the language.

[Bobsey (OP)]

I know we can make partial vacuums

On a big enough scale, the universe is a pretty good partial vacuum.

Vaccuums have vac pressure , I don't think the universe has a vac pressure

[Bobsey (OP)]

I say again: space is a vacuum. The universe is mostly space, plus some matter. Do not confuse "universe" and "space"- this is a science forum, not a bunch of bad journalists torturing the language.

I say again , but space is't devode of all matter

[Kryptid]

Steve?

Thebox, Starlight, DarkKnight or whatever you prefer to be called.

The universal volume , isn't a empty set , vector space has particels and comets passing through it all the time , it is never really empty space . It can't be a vacuum when it isn't devode of all matter .

You all explained a vaccum is devode of all matter , space , the universe , is't devode of all matter .

I ca't understand why you cosider space is a vacuum when it isn't devode of mattter .

You're arguing semantics and I don't really get why you're so hung up on this.

As an analogy, let's use the word "ocean" as an example. An ocean is defined as being made of water. That's simple enough. But if I started to argue that an ocean isn't really an ocean because it has islands in it (which aren't made of water), then that would be similar to what you are arguing. The ocean is what is between the islands.

Vaccuums have vac pressure , I don't think the universe has a vac pressure

What is "vac" pressure?

[Bobsey (OP)]

Steve?

Thebox, Starlight, DarkKnight or whatever you prefer to be called.

The universal volume , isn't a empty set , vector space has particels and comets passing through it all the time , it is never really empty space . It can't be a vacuum when it isn't devode of all matter .

You all explained a vaccum is devode of all matter , space , the universe , is't devode of all matter .

I ca't understand why you cosider space is a vacuum when it isn't devode of mattter .

You're arguing semantics and I don't really get why you're so hung up on this.

As an analogy, let's use the word "ocean" as an example. An ocean is defined as being made of water. That's simple enough. But if I started to argue that an ocean isn't really an ocean because it has islands in it (which aren't made of water), then that would be similar to what you are arguing. The ocean is what is between the islands.

Vaccuums have vac pressure , I don't think the universe has a vac pressure

What is "vac" pressure?

Suck the air out of a plastic bottle , it collapses under the vac pressure . Thats what I mean by vac pressure .

Your oceans and Islands are all within the set volume , you are looking from within the volume raather than an external view of the volume with all due respect .

If you removed the islands and oceans from the set , then you'd be left with a empty set

I'm hung up on this because I think science should be precise in explanation with no room or doubt for critism .

[Bored chemist]

Suck the air out of a plastic bottle , it collapses under the vac pressure . Thats what I mean by vac pressure .

Why did you invent a worse way of saying air pressure or external pressure?

[Bored chemist]

I say again: space is a vacuum. The universe is mostly space, plus some matter. Do not confuse "universe" and "space"- this is a science forum, not a bunch of bad journalists torturing the language.

I say again , but space is't devode of all matter

Nothing is devoid of all matter.
There is no true vacuum.
All you can hope for is a partial vacuum and, on a big scale, the universe is a pretty good partial vacuum.

[Bored chemist]

I think science should be precise in explanation with no room or doubt for critism

You should start by learning some science.

[Origin]

If you place a marble in a container then that container wouldn't be devode of all matter .

Well there is your problem, you don't know what a vacuum is.

[Kryptid]

Suck the air out of a plastic bottle , it collapses under the vac pressure . Thats what I mean by vac pressure

That's not "vac" pressure, that's just the external air pressure crushing the bottle because it isn't balanced by the internal pressure of the bottle.

Your oceans and Islands are all within the set volume , you are looking from within the volume raather than an external view of the volume with all due respect .

If you are within the Universe (which you are), then you are "looking from within the volume" just as a person on an island would be "looking from within the volume" of the ocean. The analogy is still perfectly apt.

If you removed the islands and oceans from the set...

...then you would no longer be talking about an appropriate analogy, so it's irrelevant.

I'm hung up on this because I think science should be precise in explanation with no room or doubt for critism .

You're not arguing the explanation (a vacuum isn't an explanation, it's a concept), you're arguing the definition. A sufficient explanation of the definition has been given in this thread.

After getting banned from Scienceforums.net for denying the expansion of space based on bad arguments, you've decided to come back here and cause trouble for us again?

[Bobsey (OP)]

You're not arguing the explanation (a vacuum isn't an explanation, it's a concept), you're arguing the definition. A sufficient explanation of the definition has been given in this thread.

I googled the definition and it says a vacuum is

vacuum, space in which there is no matter or in which the pressure is so low that any particles in the space do not affect any processes being carried on there. It is a condition well below normal atmospheric pressure and is measured in units of pressure (the pascal). A vacuum can be created by removing air from a space using a vacuum pump or by reducing the pressure using a fast flow of fluid, as in Bernoulli’s principle.

The universe space is not without matter . You are arguing that something that has lots of matter in it is a vacuum and I disagree because the space has matter in it . Definition disgrees with you not me .

[Bobsey (OP)]

If you place a marble in a container then that container wouldn't be devode of all matter .

Well there is your problem, you don't know what a vacuum is.

Consider a vector space and we call this vector the earths orbital path . The vector is a empty set , what you call a vacuum . When the earth changes position as it travels the vector , the earth occupies the vector space it has moved too . The empty set isnt totally empty because the earth occupies a portion of the set .

{1}→{}

[Bobsey (OP)]

denying the expansion of space based on bad arguments, you've decided to come back here and cause trouble for us again?

Expansion of space ? What do you mean by that  ?

Causing trouble ?

I do't understand what you talking about , do you find questioing a subject offensive ?

[evan_au]

a vacuum, space in which there is no matter ... A vacuum can be created by removing air from a space using a vacuum pump

In physics, we can also mathematically remove the air from a space.

Assumptions
In physics we often start with a few simplifying assumptions:
- Air is 80% nitrogen, so let's assume that it is 100% nitrogen
- Lets assume that nitrogen gas is a lot of little balls bouncing around, with space (vacuum) in between them*
- Lets assume that liquid nitrogen is a lot of little balls jostling around, with no space in between them

Data
- The density of nitrogen gas at sea level is 1.25 grams per liter
- The density of liquid nitrogen is 807 grams per liter

Calculation
The volume taken up by the tiny nitrogen "balls" in 1 litre container of nitrogen gas = 1.25/807 = 0.0015 liters, or 1.5 ml.
- The remaining 0.9985 litres (99.85%) is vacuum

Conclusion
Air at sea level is 99.85% vacuum.

Check calculation
The refractive index of liquid nitrogen is 1.25
- ie light is slowed down by a factor of 1.25 when passing through liquid nitrogen.
- Air is composed of 99.85% vacuum + 0.15% matter (from above)
- If light is slowed by the presence of matter, then the refractive index of air should be somewhere around 1 + 0.25x0.0015 = 1.0004
- Which is not too far off the measured value of 1.0003 as the refractive index of air.
- So light is slowed by a factor of 1.0003 when passing through air, compared to the speed if we physically (or mathematically) removed all the matter from air.

*This has a historical precedent in assuming "a spherical cow in a vacuum" when determining whether "a cow jumped over the Moon"...

[Colin2B]

Causing trouble ?

I do't understand what you talking about , do you find questioing a subject offensive ?

No, but inventing rubbish is offensive:

Consider a vector space and we call this vector the earths orbital path . The vector is a empty set , what you call a vacuum . When the earth changes position as it travels the vector , the earth occupies the vector space it has moved too . The empty set isnt totally empty because the earth occupies a portion of the set .

{1}→{}

Sufficient and accurate answers have been given and will help others understand.

[Bored chemist]

You suppose to be English but the americans own your asses .

I'm not aware of any mass purchases of English donkeys by the Americans.

[alancalverd]

I think science should be precise in explanation with no room or doubt for critism .

It is, which is why you are wrong. There's little point shouting in English if you are in France, or reasserting your own ignorance of scientific terminology in a science forum.

[evan_au]

Hey...  Does anyone have any comments on my back-of-the-envelope calculation of air being 99.85% vacuum?

Especially the part where I try to derive the refractive index of air from the refractive index of liquid nitrogen
- The method I used for that calculation used a lot of hand-waving
- What would be a better method of calculating it?

[Bored chemist]

Hey...  Does anyone have any comments on my back-of-the-envelope calculation of air being 99.85% vacuum?

Especially the part where I try to derive the refractive index of air from the refractive index of liquid nitrogen
- The method I used for that calculation used a lot of hand-waving
- What would be a better method of calculating it?

While your calculation isn't precise, it's a whole lot better than lots of the ideas put forward in this thread.
Ignoring the oxygen is not a serious problem because the refractive indices of O2 and N2 are pretty similar.


It's possible to measure the speed of light in a gas at varying pressures and then plot a graph and extrapolate to zero pressure, which will give you the speed of light in a vacuum.