# Density of space

1. Mar 26, 2005

### 1123581321

What is the currently accepted 'density of space'? different sources i read said it was anywhere from 1 atom/m3 and others said up to 100 atoms/m3. What is right and what is not, or is there really any way to tell?

Fibonacci

2. Mar 27, 2005

### chroot

Staff Emeritus
The matter density of space varies dramatically from point to point in that space. Are you asking for the average density of the entire universe?

- Warren

3. Mar 27, 2005

### moving finger

or are you asking for the vacuum energy density?

MF

4. Mar 27, 2005

Staff Emeritus
I think the numbers Fibonacci quoted are for the interstar density in the local region, the kind of thing a spaceship from Earth might have to deal with, or exploit. One hydrogen nucleus per cubic meter used to be the quick and dirty figure cited.

5. Mar 27, 2005

### 1123581321

yes, i am looking for the interstar density, not one with lots of stars and crap. one seemed to be the main number, so i think selfAdjoint's answer is most likely correct

Fibonacci

6. Mar 27, 2005

### misskitty

I didn't know space has a density.

7. Mar 27, 2005

### meteor

The density of the interstellar medium is not uniform, there are series of bubbles where the density drops significatively. The Sun and other stars lie concretely inside the http://www.answers.com/main/ntquery;jsessionid=8jrlololm0dmg?tname=local-bubble&hl=cubic&hl=centimetre&sbid=lc01a [Broken], that has a density of 0.1 atoms/cm3.
The Local Fluff is contained inside the Local Bubble

Last edited by a moderator: May 2, 2017
8. Mar 27, 2005

### misskitty

How many bubbles is our universe made up of?

9. Mar 27, 2005

### meteor

Hi miss kitty, I don't know, but why don't you count you it by yourself in this photo?
http://antwrp.gsfc.nasa.gov/apod/ap970424.html

More seriously, I know that appart of the Local Bubble, there exist also the Loop I bubble, Loop II bubble and Loop III bubble. It would be nice to know the number of bubbles inside the Milky Way

Last edited: Mar 27, 2005
10. Mar 27, 2005

### misskitty

What? I'm confused...

The picture by the way is very awesome. So what do the loops mean? Are they circles of bubbles scientists have plotted that are close to our solar system?

11. Mar 27, 2005

### SpaceTiger

Staff Emeritus
The interstellar medium is composed of several "phases", in between which the density varies a lot. In the "hot" phase, densities are usually of order 0.001 atoms per cubic centimeter, while in the colder phase, it's typically 1 per cubic centimeter. On the other hand, at the centers of molecular clouds, things can get really dense (as high as a million per cubic centimeter). It all depends on where you look.

12. Mar 27, 2005

### misskitty

Huh, intriguing. Thanks SpaceTiger. The space doesn't seem as big as I thought it might be; then again we are talking about atomic and sub-atomic particles so 1 cubic centimeter is quite a bit.

One thing I have been contimplating lately has been how can the space between the stars be so cold and the stars themselves and the space around them be so hot? How can there be such a massive temperature difference? How did the stars begin to burn in the first place?

13. Mar 27, 2005

### SpaceTiger

Staff Emeritus
The interstellar medium is actually quite hot, for the most part. Even the cold phase is about 100 times hotter than on the surface of the earth. Only in the centers of molecular clouds do things get really cold.

It depends on how you define "cold", though. Our human sensation of cold has to do with total energy deposition on our skin, which depends on both density and temperature.

14. Mar 27, 2005

Staff Emeritus

That defintion of hot just means the particles are moving fast. The definition of absolute temperature is just the average speed of the particles, nothing said about their density. But as Space Tiger suggested, if you had the misfortune to be immersed in such a region of space, particle speed would just mean you were irradiated while freezing to death, assuming you hadn't already exploded from internal pressure!

15. Mar 27, 2005

### SpaceTiger

Staff Emeritus
I can't tell if you're agreeing with me or not. The density dependence I spoke of was referring only to the magnitude of our "sensation" of hot and cold. In other words, if we're sitting in 10^4 K interstellar gas with densities of one per cubic centimeter, we won't feel "hot".

16. Apr 1, 2005

### misskitty

Wait, whoa! WHAT?!?! Self, you have been so patient with my ignorace, but could you expand on that for me?

Ya, got my attention this time. Not that you didn't have it before.

17. Apr 1, 2005

### whozum

Temperature is the measure of kinetic energy of the particles in an atom.

In space, pressure is nearly nonexistant due to the lack of atmosphere, this will cause your body to explode because the inside of your body is pressurized, my guess is at a pressure of 1 atm.

18. Apr 1, 2005

### misskitty

So wait, if space has a lack of atmosphere, then how and why does it form around the planets and how they pull matter into them when they first start out?

19. Apr 1, 2005

### turbo

if you are commenting on the statement about freezing to death while you are being irradiated, here's an analogy.

If someone touched your skin with a thin accupuncure needle at 300 degrees F, you would feel it like a prick on the skin and the temperature of the needle would rapidly approximate that of your skin. If someone touched your skin with a 16 penny nail at 300 degrees F it would hurt. If you put your hand on an anvil that is at 300 degrees, you would suffer severe burns. The damage is a function both of the energy level of the source and the mass (or flux in the case of radiation) of the source. Another example: You can go skiing on a bright (not even fully sunny) day and freeze your toes off all day long and end up with a severe sunburn if you're not careful. It's worse on more northern mountains with colder temperatures and less atmosphere to protect you from the UV. You don't even realize the UV is cooking you until it is too late.

Last edited: Apr 1, 2005
20. Apr 1, 2005

### whozum

Space doesnt form around plantes, planets form in space. Planets attract matter towards them via gravity.

Atmosphere is the collection of gasses and matter. For example, earth's atmosphere is made up of nitrogen, oxygen, carbon dioxide, etc.

21. Apr 1, 2005

### misskitty

Ah, ok. Makes sense, I think. Pretty sure. The first part of my question was just asking how atmosphere forms around planets in space.

Whozum, you must think I am a complete and utter air head.

Turbo, great analogy. I guess I'll ahve to be more careful with my little pyro tendencies. just kidding.

Whozum, where does the matter that "starts" the planet get the gravity to attract smaller particles and eventually larger particles? Does it just have it?

22. Apr 1, 2005

### whozum

If I remember correctly, the big bang didnt disperse matter perfectly evenly, so there were regions of space that were relatively denser than others. From there, the gravity in this region brought these particles together, and those particles, now armed with a stronger gravitational force, brought more together, and so forth.

Air head? Nonsense. A student. :)

23. Apr 1, 2005

### misskitty

What would cause the big bang to unevenly distribute the matter?

24. Apr 2, 2005

### Chronos

It didn't, which is fortunate for us. The entire universe would have recollapsed back upon itself before we had a chance to come into being had the initial distribution of matter not been extremely smooth.

25. Nov 3, 2009

### timothyjr

These posts seem to be more about the density of matter IN space. What about any thoughts to the density OF space. There must be some value of space itself that gives the speed of light its constant value?