# Properties of a vacuum

1. Aug 28, 2009

### Razael

I've just got around to asking this question, and a quick Google search gave me nothing.

What is a vacuum made of? What is the "space" that matter usually occupies?

2. Aug 28, 2009

### Gear300

From what I know, a "vacuum" is actually composed of matter-antimatter collision effects (I may be completely off).

3. Aug 28, 2009

### Electrocuted

A vacuum can be described as a region of space with negative pressure. It does not consist of any medium, but rather a region where there is nothing. Matter can occupy itself in a region of vacuum or atmospheric conditions; of course interesting properties may arise such as the casimir effect when subjected to vacuum environments.

4. Aug 29, 2009

### Bob_for_short

In a usual sense vacuum is a space from which all material bodies have been removed. It is a space than can potentially be occupied with something.

5. Sep 9, 2009

### Razael

Maybe if I rephrase it it'll be easier to understand.

Basically, what is the difference between a vacuum in our universe ("empty space") and what our universe is expanding into? Are there any theories?

6. Sep 9, 2009

### Rajini

some cents..
vacuum in universe is less than 10^-12 torr or even less (but not zero)..some ppl. like engineers usually refer low pressure (less than atm. pr.) as -ve pr.

7. Sep 9, 2009

8. Sep 9, 2009

### fawk3s

correct me if im wrong (which i usually am lolz), but how can vacuum have negative pressure when there's nothing in it?
the effect of "sucking in" comes from the pressure balancing in 2 different spaces.

9. Sep 9, 2009

### fatra2

Hi there,

We say that our Universe is expanding. Of course, not in the sense that a balloon blows up. Our Universe is define as wherever there is space and time. Therefore, space, even empty space (vaccum) is part of our Universe. The expansion comes from the fact that there is more and more space in our Universe as time goes by.

Cheers

10. Sep 9, 2009

### fawk3s

ah yes, our universe is basically expanding into nothing. while doing it, creating space and time.

11. Sep 9, 2009

### Staff: Mentor

That wording can be misleading. It is better to say the universe is not expanding into anything.

12. Sep 12, 2009

### Bob S

Hi Razael-
Our intergalactic vacuum primarily has a few molecules of primordal gas per cubic meter (Compare to a few Avagadro numbers here on Earth), a few photons from the cosmic microwave background and starlight, a few neutrinos, and an occasional cosmic ray. It also has two interesting properties, the dielectric permeability and magnetic permittivity of free space, which are constant and related to the speed of light. "Vacuum energy" and associated virtual particles is only associated with strong Coulomb fields, which are not present in intergallactic space.
Bob S