What is the True Density of Space?

[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?

Thanks in advance,
Fibonacci

 

[chroot]

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

 

[moving finger]

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

or are you asking for the vacuum energy density?

MF

 

[selfAdjoint]

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.

 

[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

 

[misskitty]

I didn't know space has a density.

 

[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 , that has a density of 0.1 atoms/cm³.
The Local Fluff is contained inside the Local Bubble

 

[misskitty]

How many bubbles is our universe made up of?

 

[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

 

[misskitty]

Hi miss kitty, I don't know, but why don't you count you it by yourself in this photo?

What? I'm confused...

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

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?

 

[SpaceTiger]

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.

 

[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?

 

[SpaceTiger]

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?

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.

 

[selfAdjoint]

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.

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!

 

[SpaceTiger]

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.

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".

 

[misskitty]

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!

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.

 

[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.

 

[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?

 

[turbo]

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.

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.

 

[whozum]

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?

Space doesn't 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.

 

[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?

 

[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. :)

 

[misskitty]

Glad to know you don't think I'm an air head.

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

 

[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.

 

[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?

 

[DaveC426913]

This thread has been bumped after 4 years of minding its own business. Nothing wrong with that in and of itself...

... but it did cause me a bit of a start to see Self-Adjoint again...

 

[Chronos]

See permissivity and permitivity, but, the larger question is harder. It takes a lot of fancy math and observational evidence to pin it down, and no one knows why c is c, or h is he. It is clear, however, such values are necessary to permit observers like us ask the question. I am not a multiverse fan, but, it is logical. In an infinite universe, at least one patch must permit physical parameters conducive to life to exist. Any theory that forbids our existence is illogical.

 

[Wallace]

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?

Thems be the line of thinking that lead to the aether theory that was busted by a combination of the Michelson and Morley experiment and the theoretical advances of Einstein, Hilbert and others.

Space itself is not a thing in General Relativity. That's actually a really important (and tricky) concept to try and get your head around. You can't uniquely talk about that some region of space does without specifying a co-ordinate system, which General Relativity demands not be unique. Therefore anytime you try and pin down a property of some region of space, you have to make arbitrary co-ordinate choices which make your interpretations equally arbitrary.

I'm getting a little long winded, but the important thing is that space does not have a density, the constants of nature are what they are for reasons not yet understood. There is the question of a possible non-zero vacuum energy density, but that is a different question not related to the speed of light (at least as far as we know!).

As an aside, holy threadcromancy Batman! I thought for a moment that Space Tiger was back, but not to be...

 

[timothyjr]

Density is probably not the right word... maybe a coefficient of space would be better... and not of a unique region, but of allspace. I think it exists and I am going to keep looking for "the reasons not yet understood".

 

[Ich]

You can attribute some kind of an index of refraction to space, which defines the speed of light. That wourks perfectly for light, but not for other things. For the complete theory, you need six numbers (I think).