How can the vacuum of space be "empty"

[Lightmeow]

Today in science class we were talking about waves, you know, sound waves and radiation and other types of waves. So, the science teacher was saying that sound is basically just a mechanical latitudinal wave. So then, I asked him if sound travels in a vacuum. He said no, because there is nothing in a vacuum. No air or nothing. I asked him why, and he said that he didn't know. I understand that space doesn't have any air in it, but how can there be nothing at all? There must be something in the vacuum like air, right? Can you tell me, I was mind blown today. I always thought that in space there was a different form of air, or something that sound could go through, but nothing is crazy!!! Please Explain, I hope you can...

 

Joshua

[mathematic]

Sound waves require a material to propgate. In the vacuum of space there are photons and neutrinos, but nothing to carry sound.

[swansont]

That's what a vacuum is: the (relative) lack of matter.

[pzkpfw]

Today in science class we were talking about waves, you know, sound waves and radiation and other types of waves. So, the science teacher was saying that sound is basically just a mechanical latitudinal wave. So then, I asked him if sound travels in a vacuum. He said no, because there is nothing in a vacuum. No air or nothing. I asked him why, and he said that he didn't know. I understand that space doesn't have any air in it, but how can there be nothing at all? There must be something in the vacuum like air, right? Can you tell me, I was mind blown today. I always thought that in space there was a different form of air, or something that sound could go through, but nothing is crazy!!! Please Explain, I hope you can...

 

Joshua

 

If there was anything materially significant in space, our Planet would be having to push it's way through it - we'd see the turbulent effects on our atmosphere, and our orbit would slow, and eventually we'd all drop into the Sun. Hooray for the (near) vacuum of space!

[Sensei]

You can see and hear on your own ears how it changes with latitude in rocket with attached video camera:

[Janus]

Sure, there is something in space, its just that there is very little. In interplanetary space there is about 1 atom per cubic centimeter. In one cubic centimeter of air at the surface of the Earth, there are about 5 x 10^22 atoms. So as you can see, the atoms in air are much more closely bunched together than they are in space.

 

Now consider how sound travels through air. Basically, sound is vibration. For instance, if you hit a drum, it surface vibrates, this pushes back and forth on the air touching the surface of the Drum. The atoms next to the drum are pushed into the atoms next to them, and they bump into the one ones next to them and so on. What you end up with is a bunch of atoms squeezed together and then a space of fewer atoms, etc. It is these concentrations and rarities of atoms moving away from the drum which make up sound waves. This all works because the atoms in air are so close to each other that they don't have travel very far in order to bump into another atom.

 

Now consider interplanetary space, the atom are so far apart from each other that any given atom being pushed in a random direction could travel several centimeters before running into another atom, while passing between the gaps separating other atoms. You just are not going to get the organized waves of compression you get with normal air that is needed to carry sound waves.

 

As to why atoms are spread out so thin in space, it is because there isn't really a lot of matter to go around. If you took all the matter in the universe and spread it out evenly, you wouldn't even notice a difference in the number of atoms per cc, it would be that small of a change. So the real question isn't "why isn't there air in space", but "why do we have air that is as thick as it is on the surface of the Earth. The answer is gravity. All matter in the universe is attracted to itself. As a result, it tends to clump up into stars, planets, moons, etc. If the clump is large enough, like the Earth, its gravity can pull a thin skin of gasses around it and it will have an atmosphere, which in our case is thick enough to do a fair job of carrying sound waves.

[Sensei]

In one cubic centimeter of air at the surface of the Earth, there are about 5 x 10^22 atoms.

 

There is ~2.68*10^22 molecules of gas in 1 L @ T=273 K and p=101325 Pa

So there is ~2.68*10^19 molecules in 1 cm^3 at sea level.

For diatomic gases, quantity of atoms must by multiplied by 2.

5.36*10^19 atoms per cm^3

 

1 cm^3 of water has 3.3456*10^22 molecules.

Edited March 7, 2014 by Sensei

[hoola]

in even total empty space there are things called "virtual particles" that pop in and out of existence that are little understood so far...I see these particles as analogous to the air of earth as an "air of space", but have very different properties...it's a very exciting prospect to find out what they are and if they affect things other than the cosmic expansion, of which they may be causing...they are also sometimes referred to as dark energy...

[Spyman]

Today in science class we were talking about waves, you know, sound waves and radiation and other types of waves. So, the science teacher was saying that sound is basically just a mechanical latitudinal wave. So then, I asked him if sound travels in a vacuum. He said no, because there is nothing in a vacuum. No air or nothing. I asked him why, and he said that he didn't know. I understand that space doesn't have any air in it, but how can there be nothing at all? There must be something in the vacuum like air, right? Can you tell me, I was mind blown today. I always thought that in space there was a different form of air, or something that sound could go through, but nothing is crazy!!! Please Explain, I hope you can...

 

Joshua

If you have a container with a mechanism to push out air like a cylinder with an airtight piston, what do you think would remain in the cylinder behind the piston when it has moved forward and pushed out all air, if not empty space?

Except for the mechanism such as the rod and the piston the cylinder would be an empty hollow container, there would be nothing between the rod and the walls of the cylinder, only empty space.

 

And actually it's much worse than that, even things like air, water, earth and the atoms matter are made of are mostly empty space inside.

 

If you could magnify a volume of air so that you could see individual atoms in the air moving around, then what is between them?

The temperature of an ideal monatomic gas is a measure

of the average kinetic energy of its atoms. The size of

helium atoms relative to their spacing is shown to scale

under 1950 atmospheres of pressure. The atoms have a

certain, average speed, slowed down here two trillion fold

from room temperature.

http://en.wikipedia.org/wiki/Kinetic_Theory

 

And if you would zoom in even more such that you could see the nucleus of the atoms, then what is between the electrons around them?

An illustration of the helium atom, depicting the nucleus

(pink) and the electron cloud distribution (black). The

nucleus (upper right) in helium-4 is in reality spherically

symmetric and closely resembles the electron cloud, although

for more complicated nuclei this is not always the case.

The black bar is one angstrom (10⁻¹⁰ m or 100 pm).

http://en.wikipedia.org/wiki/Atom

Edited March 7, 2014 by Spyman

[swansont]

If you have a container with a mechanism to push out air like a cylinder with an airtight piston, what do you think would remain in the cylinder behind the piston when it has moved forward and pushed out all air, if not empty space?

 

Simpler still is taking a small-diameter closed-end tube, filling it with a liquid and then inverting it (with the bottom in a reservoir). You will draw a vacuum in the top end; the only matter will be a small amount of vapor of whatever fluid you have, with the amount depending on its vapor pressure.

[swansont]

!

Moderator Note

 

Discussion on a possible relation between virtual particles and dark energy has been split

http://www.scienceforums.net/topic/82066-is-dark-energy-comprised-of-virtual-particles/

 

[Enthalpy]

Pulling a piston or a liquid from a cylinder will make an extremely bad vacuum, full of gas. First, you have the residual volume of gas in the cylinder. Then, you have all walls outgassing. And if applying, vapour pressure.

 

Vacuum needs seals, and there are residual volumes around seals.

 

Getting a vaccum as good as interplanetary space is damned difficult on Earth, and needs to bake all walls, use a cascade of special pumps and so on, and even then, there are still plenty of molecules.

[pantheory]

Today in science class we were talking about waves, you know, sound waves and radiation and other types of waves. So, the science teacher was saying that sound is basically just a mechanical latitudinal wave. So then, I asked him if sound travels in a vacuum. He said no, because there is nothing in a vacuum. No air or nothing. I asked him why, and he said that he didn't know. I understand that space doesn't have any air in it, but how can there be nothing at all? There must be something in the vacuum like air, right? Can you tell me, I was mind blown today. I always thought that in space there was a different form of air, or something that sound could go through, but nothing is crazy!!! Please Explain, I hope you can...

 

Joshua

 

Within the last year I recall reading of how sound moves in space. Although classically sound cannot move in a pure vacuum, space in not a pure vacuum, although it is very close to it. There might be roughly about one hydrogen atom or proton per cubic meter of intergalactic space, amongst a much rarer occurrence of other atoms and nuclei. The energy of a particle can be transferred to another and so on in a radial or linear pattern. Since this energy can be created in pulses, a wave pattern can develop which through instrumentation can be perceived as sound.

 

Modern theory proposes many other possibilities concerning an "atmosphere" (field) of background particles that permeates all of reality. Such theories are dark matter, a Higgs field, a graviton field, quantum foam, and modern theories concerning the existence of an aether, which was the prevailing mainstream theory before the 20th century.

 

http://en.wikipedia.org/wiki/Aether_theories

Edited March 8, 2014 by pantheory